The continuum between Cadomian orogenesis and …al'07.pdf · The continuum between Cadomian orogenesis and opening ... 2007, The continuum between Cadomian orogenesis and opening

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61

Geological Society of AmericaSpecial Paper 423

2007

The continuum between Cadomian orogenesis and opening of the Rheic Ocean: Constraints from LA-ICP-MS U-Pb zircon dating

and analysis of plate-tectonic setting (Saxo-Thuringian zone, northeastern Bohemian Massif, Germany)

Ulf Linnemann*Staatliche Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Königsbrücker Landstrasse 159,

D-01109 Dresden, Germany

Axel GerdesInstitut für Geowissenschaften, Mineralogie, Johann Wolfgang Goethe-Universität Frankfurt am Main, Senckenberganlage 28,

D-60054 Frankfurt am Main, Germany

Kerstin DrostStaatliche Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Königsbrücker Landstrasse 159,

D-01109 Dresden, Germany

Bernd BuschmannTU Bergakademie Freiberg, Geologisches Institut, Bernhard-von-Cotta-Strasse 2, D-09599 Freiberg, Germany

This paper is dedicated to Jean-Jacques Chauvel (1935–2004)

ABSTRACT

Sediment provenances and magmatic events of Late Neoproterozoic (Ediacaran) and Cambro-Ordovician rock complexes from the Saxo-Thuringian zone are con-strained by new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of detrital zircons from fi ve sandstones and magmatic zircons from an ignimbrite and one tuffi te. These geochronological results in combination with the analysis of the plate-tectonic setting constrained from fi eld observations, sedimentological and geochemical data, and trends of the basin development are used to reconstruct Cadomian orogenic processes during the Late Neoproterozoic and the earliest Cambrian. A continuum between Cadomian orogenesis and the opening of the Rheic Ocean in the Cambro-Ordovician is supported by the data set.

*[email protected]

Linnemann, U., Gerdes, A., Drost, K., Buschmann, B., 2007, The continuum between Cadomian orogenesis and opening of the Rheic Ocean: Constraints from LA-ICP-MS U-Pb zircon dating and analysis of plate-tectonic setting (Saxo-Thuringian zone, northeastern Bohemian Massif, Germany, in Linnemann, U., Nance, R.D., Kraft, P., and Zulauf, G., eds., The evolution of the Rheic Ocean: From Avalonian-Cadomian active margin to Alleghenian-Variscan collision: Geological Society of America Special Paper 423, p. 61–96, doi: 10.1130/2007.2423(03). For permission to copy, contact [email protected]. ©2007 Geological Society of America. All rights reserved.

62 Linneman et al.

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INTRODUCTION

The Cadomian orogeny comprises a series of complex sedi-mentary, magmatic, and tectonometamorphic events that spanned the mid-Neoproterozoic (ca. 650 Ma) to the earliest Cambrian (ca. 540 Ma). Rock units formed by the Cadomian orogeny are commonly referred to collectively as Cadomian basement. Owing to similar contemporaneous orogenic processes in the Avalonian microplate, the collective term Avalonian-Cadomian orogeny has also been used in the modern literature. Peri-Gondwanan ter-ranes, microcontinents, and crustal units in central, western and eastern Europe and in north Africa are affected by the Cadomian orogeny. Related orogenic events known as the Avalonian orog-eny, are known from the Appalachians (eastern United States and Atlantic Canada) and from the non-Laurentian part of Ire-land and the British Isles. Baltica escaped Avalonian-Cadomian orogenic activity, although late Precambrian orogenic events of “Cadomian affi nity” have been recognized in the Urals and the Timanides on the periphery of Baltica (Roberts and Siedlecka 2002; Glasmacher et al., 2004).

The Cadomian orogeny was fi rst defi ned in the North Armorican Massif in France on the basis of the unconformity that separates deformed Precambrian rock units from their Early Paleozoic (Cambro-Ordovician) overstep sequence. In central and western Europe this unconformity is commonly referred to as the Cadomian unconformity. The youngest metasedimentary rocks affected by Cadomian deformation may be earliest Cam-brian in age, and many geologists assume that the fi nal stages of Cadomian orogenesis were spatially diachronous, lasting from the latest Neoproterozoic to the earliest Cambrian. From this viewpoint the term Cadomian basement includes Neoproterozoic (Ediacaran) to Early Cambrian sedimentary, igneous, and meta-morphic complexes, although the stratigraphic range of the rocks involved changes from region to region.

The Cadomian unconformity was fi rst described from Rocreux near Caen (Normandy) by Bunel (1835), although it is often attributed to Dufrenoy (1838), who published the fi rst

drawing. The wider geographic extent of the unconformity in central Brittany was recognized by Dufrenoy (1838) and Barrois (1899). The fi rst illustration of the unconformity from Brittany was published by Kerforne (1901).

Cadomus and Cadomum are old Latin terms for the modern city of Caen and are the source of the name of the orogeny. The term discordance cadomienne was fi rst used by Bertrand (1921). The type locality of the Cadomian unconformity is located on the northern edge of the village of Jacob Mesnil (Rocreux), close to Bretteville sur Laize near Caen (Normandy). The best illustration of the unconformity at Rocreux was published by Graindor (1957).

In some publications, the term Pan-African orogeny is used in the same sense as the Cadomian orogeny, because both events were related to the Gondwana supercontinent in the late Precam-brian and occurred at more or less the same time. The main differ-ence between the two orogenic events is their position within the confi guration of the Gondwana supercontinent in Neoproterozoic time. The crustal units affected by the Pan-African orogeny are located between the cratons that assembled Gondwana and, in most cases, refl ect continent-continent collision (see compilation of Windley, 1995). In contrast, the Cadomian orogen, or alterna-tively, the Avalonian-Cadomian orogenic belt, was a peripheral orogen at the edge of the Gondwanan supercontinent and is char-acterized by orogenic processes similar to those of the present-day Andes and Cordilleran chains of the Americas and western Pacifi c (Murphy and Nance, 1991; Nance and Murphy, 1994; Buschmann, 1995; Linnemann et al., 2000, 2004; Nance et al., 2002).

On the basis of provenance studies based on U-Pb ages of detrital zircon grains from sedimentary rocks and inherited zir-cons in igneous rocks, in combination with Nd-Sr-Pb isotope analyses and paleomagnetic and paleobiogeographic data, most geologists accept that the largest part of the Cadomian basement of central and western Europe was formed at the periphery of the West African craton of the Gondwana supercontinent (e.g., Linnemann et al., 2004; Murphy et al., 2004). Remnants of old cratonic basement are represented only by the Icartian basement

In our model, the early stage of the Cadomian evolution is characterized by a Cor-dilleran-type continental magmatic arc, which was established at the periphery of the West African craton between ca. 650 and 600 Ma. Subsequently, at ca. 590–560 Ma, a back-arc basin was formed behind the Cadomian magmatic arc. The back-arc basin was closed between ca. 545 and 540 Ma, leading to the development of a short-lived Cadomian retroarc basin. Subsequently, a mid-oceanic ridge was subducted under-neath the Cadomian orogen. Slab break-off of the subducted oceanic plate resulted in increased heat fl ow, leading to voluminous magmatic and anatectic events that culmi-nated at ca. 540 Ma. Oblique incision of the oceanic ridge into the continent caused the formation of rift basins during the Lower to Middle Cambrian. This process con-tinued from the Middle to Upper Cambrian, fi nally caused the opening of the Rheic Ocean in the Lower Ordovician.

Keywords: Peri-Gondwana, Cadomian orogeny, Bohemian Massif, Saxo-Thuringian zone, Cadomia, Avalonia, Rheic Ocean, U-Pb zircon dating, provenance.

The continuum between Cadomian orogenesis and opening of the Rheic Ocean 63

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(2.06–2.01 Ga) of the Armorican Massif, and the Svetlik (2.1–2.05 Ga) and Dobra gneisses (1.38 Ga) of the Bohemian Mas-sif. These Meso- to Paleoproterozoic gneiss complexes coupled with abundant Archean to Paleoproterozoic detrital zircon grains in Neoproterozoic sediments indicate that most of the Cadomian “basement” developed on thinned older cratonic crust and that the Neoproterozoic to Cambrian siliciclastic sediments result from eroded older basement slices.

Nance et al. (2002) proposed a Cordilleran model for the evolution of the Neoproterozoic to Cambro-Ordovician rock com-plexes in the Avalonian part of the “Avalonian-Cadomian orogenic belt,” drifted off as a separate microcontinent during the late Cam-brian. They suggested that the formation and separation of Ava-lonia was controlled by a plate-tectonic evolution similar to that presently observed at the western margin of the North American plate in Baja California. Over the past 30 Ma, this area has been affected by terrane accretion, subduction-related processes, ridge-trench collision, and rifting processes. As shown in this article, these processes may also account for the sedimentological and magmatic evolution observed in the Neoproterozoic-Paleozoic basement complexes of the Saxo-Thuringian zone, which lies at the northeastern periphery of the Bohemian Massif. Parts of this zone were less affected by the Variscan orogeny and, thus, forms an ideal area to study sedimentological and magmatic events that occurred during the Neoproterozoic and Cambro-Ordovician.

In this article, we present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb data for detrital zircon grains to constrain the provenance of selected sediments of the Saxo-Thuringian zone. In addition, data from zircons in well-defi ned igneous rocks provide new time markers for the area’s magmatic evolution. These geochronological data, in conjunction with fi eld relations and published results, are used to defi ne the plate-tectonic setting(s) of Neoproterozoic to Cam-bro-Ordovician rock units of the Saxo-Thuringian zone. Finally, the combined data set is used to present a tentative model for the evolution of the Cadomian basement of the Saxo-Thuringian zone, which starts with the formation of a marginal Cadomian orogen between ca. 650 and 540 Ma and ends with the opening of the Rheic Ocean in the Cambro-Ordovician.

GEOLOGIC SETTING

Bohemian Massif

The Bohemian Massif forms the central part of the European Variscides and is subdivided into two principal zones, the Saxo-Thuringian zone to the north and Moldanubian zone to the south (Kossmat, 1927). In addition, the marginal Moravo-Silesian zone rims the Bohemian Massif in its eastern part. To the northwest, the massif is bordered by the Mid-German Crystalline zone, which is assumed to represents an important Variscan suture zone, perhaps the Rheic suture (Kroner et al., 2003, this volume; Zeh and Wunderlich, 2003; Zeh et al., 2003, 2005; Linnemann et al., 2004). The latter was closed by oblique collision between the

Saxo-Thuringian zone (Cadomia) and the Rhenohercynian zone (East Avalonia) during the Late Devonian to Early Carbonifer-ous (Oncken, 1997; Kroner et al., 2003, this volume; Zeh et al., 2003, 2005). To the south and southeast the Bohemian Massif is overthrust by Meso-and Cenozoic rocks of the Alps and the Car-pathians. Additional components of the Bohemian Massif are the Teplá-Barrandian unit and the Moravo-Silesian zone. The oldest units of the Bohemian Massif are remnants of Paleo- to Meso-proterozoic cratonic basement slivers, such as the Dobra gneiss (1.38 Ga) and the Svetlik gneiss (2.1–2.05 Ga).

The Bohemian Massif is the most prominent inlier of basement rocks in central Europe (Fig. 1) and records a com-plex Neoproterozoic to Paleozoic history that includes the Cadomian and Variscan orogenies. Some rock units (e.g., the Erzgebirge Mountains) locally experienced ultra-high pressure metamorphic conditions during the Variscan orogeny with the formation of diamond-bearing rocks (Massonne, 1998). Most marginal rock units and inliers, however, were essentially less affected by the Variscan tectonometamorphic overprint. These rock units comprise Neoproterozoic to Paleozoic successions at the northern margin of the Saxo-Thuringian zone and the Teplá-Barrandian unit (Fig. 1).

The Bohemian Massif has been traditionally interpreted to be part of the Armorica microplate as defi ned by Van der Voo (1979). However, more recent studies (Tait et al., 1997; McKer-row et al., 2000) have assumed that the Armorican microplate was not a coherent block, but comprises several units. Thus, Tait et al. (1997) suggested the term Armorican terrane assemblage, which includes Neoproterozoic and Paleozoic basement units exposed in northern and southern France and in central Europe.

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64 Linneman et al.

spe423-03 page 64

For the late Neoproterozoic to Cambro-Ordovician base-ment rocks relevant to Cadomian and post-Cadomian orogenic processes, we use the term Cadomia (sensu Nance and Murphy, 1996), which comprises Cadomian basement rocks (with interca-lated older cratonic blocks) of the Armorican Massif, the French Massif Central, and the Bohemian Massif with the exception of the Brunovistulian of the Moravo-Silesian zone (Fig. 1).

Based on new geochronological results, the Cadomian base-ment of the Bohemian Massif can be subdivided into Avalonian-type and Cadomian-type units sensu Murphy et al. (2004). Ava-lonian-type units contain detrital zircon grains of Mesoprotero-zoic age, which are assumed to have formed in a juvenile crust between 1.3 and 1.0 Ga. In contrast, Cadomian-type rock units show few or no zircons with ages in the range 1.7–.75 Ga and are dominated by detritus and inherited zircons derived from the West African craton (2.05 Ga and older; Murphy et al. 2004).

To date, all U-Pb zircon provenance studies indicate that the Neoproterozoic to Paleozoic sediments of the Saxo-Thuringian zone, the Teplá-Barrandian unit, and the Moldanubian zone have a west African provenance (Linnemann et al. 2000, 2004; Gehm-lich, 2003; Tichomirowa, 2003; Drost et al., 2004). Thus, they belong to Cadomia sensu Murphy et al. (2004). However, proto-lith ages of ca. 2.1 Ma indicate that the Svetlik granite gneiss of the Bohemian Massif was emplaced during the Paleoproterozoic (Wendt et al., 1993, 1994). From its geological position it seems likely that this gneiss represents part of the Eburnian basement derived from the West African craton.

However, Finger et al. (2000) demonstrated that the Bru-novistulian unit in the Moravo-Silesian zone of the Bohemian Massif (Fig. 1) shows strong affi nities with Avalonia. Rocks from the Brunovistulian unit are assumed to have been derived from the recycled margin of the Amazonian craton, as suggested by U-Pb ages of inherited zircon grains (Friedl et al., 2000). The 1.38-Ma Dobra gneiss is assumed to represent a cratonic inlier that also belongs to the Avalonian part of the Bohemian Massif (Gebauer and Friedl, 1994; Friedl et al., 2004). The available ages suggest that the Bohemian Massif is divided by a suture (likely the Rheic suture) into Avalonian and Cadomian parts (Fig. 1). The Cadomian part comprises the Saxo-Thuringian and Moldanubian zones, the Teplá-Barrandian unit, and the Sudetes, whereas the Avalonian part includes the Brunovis-tulian unit of the Moravo-Silesian zone. The former “Rheic” suture is probably hidden under and/or incorporated into the Variscan fault-and-thrust belt between the Moravo-Silesian and the Moldanubian zones (Fig. 1).

Saxo-Thuringian Zone

The Saxo-Thuringian zone forms the northeastern part of the Bohemian Massif. It consists of Cadomian basement units, which are overlain by a Paleozoic overstep sequence (Fig. 2). The parau-tochthonous part of the Saxo-Thuringian zone forms a northeast–east-trending fold-and-thrust belt, which consists of the Schwarz-burg antiform, the North Saxon antiform, the Berga antiform, and

the Lausitz antiform, and the Torgau-Doberlug and Ziegenrück-Teuschnitz synclines. In addition, the Saxo-Thuringian zone is transected by the northwest–southeast-trending Elbe zone and the Franconian line (Fig. 2). In this study we use the neutral word antiform instead of the traditional term anticline, because none of the tectonostratigraphic units are typical anticlines. For example, the Lausitz antiform is a tilted horst block.

The Saxo-Thuringian zone in this article is subdivided into an internal and external domain, which show signifi cant differences with respect to their Cadomian basement evolu-tion and Paleozoic overstep sequences. The external domain is composed of the Cadomian volcanosedimentary units of the Rothstein Formation in the Torgau-Doberlug syncline and the Altenfeld Formation in the northwestern part of the Schwarz-burg antiform (Figs. 2 and 3). Both are characterized by rock units containing thick layers of massive black chert (Fig. 4A) and are assumed to have originated in a back-arc setting (Bus-chmann, 1995; Linnemann et al., 2000). These sediments are dominated by dark-gray to black distal turbidites composed of an intercalation of graywacke and mudstone bedsets. All known sedimentological and geochemical data point to an origin for the Rothstein Formation in the center of a back-arc basin devel-oped on thinned continental crust (Buschmann, 1995). Owing to its similar spatial position in the Saxo-Thuringian zone and its similarity in lithology and geochemistry, we assign the Altenfeld Formation to the same plate-tectonic setting. Zircon data suggest deposition of the Rothstein and Altenfeld forma-tions at ca. 570–565 Ma (Linnemann et al., 2000; Buschmann et al., 2001).

The Rothstein Formation is overlain by Lower to Middle Cambrian sediments (Fig. 5), whereas the Altenfeld Formation is covered by Lower Ordovician siliciclastics (Fig. 6). In contrast to the internal domain, ca. 540-Ma magmatism in the external domain is very scarce. Only a single small pre-Variscan granitoid body (the Milchberg granite) crops out in the northwestern part of the Schwarzburg antiform, where it intrudes the Altenfeld For-mation. Recent U-Pb zircon datings place that granite to the base of the Ordovician (ca. 490 Ma; U. Linnemann and A. Gerdes, unpublished data). Another important component of the external domain is the Vesser complex of Middle to Upper Cambrian age. This unique complex is characterized by rocks related to the for-mation of the oceanic crust (Bankwitz et al., 1992; Kemnitz et al., 2002). The relationship between the external domain and the Mid-German Crystalline zone to the north is unclear because of coverage by Cenozoic sediments. The bounding element of the internal domain is the Blumenau Shear Zone, which divides the Schwarzburg antiform into a northwestern and southeastern part. In our view, the Blumenau Shear Zone continues to the southern border of the Torgau-Doberlug syncline, which is also covered by Cenozoic deposits. The shear zone is a structural feature that likely originated in the Cadomian orogeny during the tectonic change from a back-arc basin to a retroarc basin setting (see below). During the Variscan orogeny, the Blumenau Shear Zone was reactivated as a sinistral shear zone (Heuse et al., 2001).


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man

crys

talli

nezo

nean

dre

late

dro

ckun

its

Sur

face

outc

rops

ofth

eM

id-G

erm

ancr

ysta

lline

zone

Nor

ther

nph

yllit

ezo

ne(C

ambr

o-O

rdov

icia

nro

ckco

mpl

ex)

Ves

ser

com

plex

(Upp

erC

ambr

ian)

Sou

ther

nph

yllit

ezo

ne(C

ambr

o-O

rdov

icia

nro

ckco

mpl

ex)

Sur

face

outc

rops

Low

tohi

ghgr

ade

orth

o-an

dpa

ra-r

ocks

Ord

ovic

ian,

Silu

rian

and

Dev

onia

nvo

lcan

o-se

dim

enta

ryro

ckco

mpl

exes

Cam

bro-

Ord

ovic

ian

toLo

wer

Car

boni

fero

usvo

lcan

o-se

dim

enta

ryro

ckco

mpl

exes

Var

isca

nan

dp

ost

-V

aris

can

ign

eou

sro

cks

(ca.

330

-30

0M

a)

Cad

om

ian

ign

eou

sro

cks

(Lo

wer

Cam

bri

an,

c.54

0-

530

Ma)

Ord

ovi

cian

gra

nit

oid

s(c

a.49

0M

a)

Laus

itzan

atex

ite

Lstgrio auizantidome cplx

Wes

tern

Laus

itzgr

anito

ids

Eas

tern

Laus

itzgr

anito

ids

Gra

nito

ids

ofth

eE

lbe

zone

(Doh

na&

Laas

gran

odio

rites

)

Gra

nito

ids

ofth

eLe

ipzi

gar

ea

Rum

burk

gran

ite(L

ausi

tzan

tifor

m)

Tour

mal

ine

gran

ite(E

lbe

zone

)

Gra

nito

ids

ofth

eS

chw

arzb

urg

antif

orm

shea

rzo

ne-r

elat

edor

thog

neis

ses

(Gro

ssen

hain

gnei

ss)

Per

mo-

Car

boni

fero

usgr

anito

ids

Upp

erC

arbo

nife

rous

rhyo

litoi

ds

Upp

erC

arbo

nife

rous

maj

orgr

anito

iddy

kes

oe

Zn

Zone

Zo

ne

12

BC

7

8

6 A

D

E

GH

4

5

3

Dre

sden

Lausit

z

H

H

(Geo

log

ical

map

wit

ho

ut

any

stra

ta y

ou

ng

er t

han

Lo

wer

Car

bo

nif

ero

us)P

raha

Cad

om

ia

i

(

on

sv

l

t

a

Ea)

aA

ure

utS

eci

Rh

Gerany m

ltB

aic

a

map

Ro

thst

ein

Kam

enz

Lei

pzi

g

oC

dia

an

m ms

iva

gin

pa

ser

F

a

b

c

d

e

Figu

re 2

. Geo

logi

cal

map

of

the

Saxo

-Thu

ring

ian

zone

in

the

nort

heas

tern

par

t of

the

Boh

emia

n M

assi

f, s

how

ing

units

of

Low

er C

arbo

nife

rous

and

old

er a

ges

and

the

dist

ribu

tion

of r

ocks

th

at r

epre

sent

the

diff

eren

t sta

ges

of C

adom

ian

basi

n de

velo

pmen

t (m

odifi

ed f

rom

Lin

nem

ann

and

Scha

uer,

1999

; Lin

nem

ann

and

Rom

er, 2

002)

. Tec

tono

stra

tigra

phic

uni

ts: 1

—Sc

hwar

zbur

g an

tifor

m (

sout

heas

tern

par

t);

2—Sc

hwar

zbur

g an

tifor

m (

nort

hwes

tern

par

t);

3—B

erga

ant

ifor

m;

4—N

orth

Sax

on a

ntif

orm

(L

eipz

ig a

rea)

; 5—

Nor

th S

axon

ant

ifor

m (

Cla

nzsc

hwitz

are

a);

6—To

rgau

-Dob

erlu

g sy

nclin

e; 7

—E

lbe

zone

; 8—

Lau

sitz

ant

ifor

m. N

eopr

oter

ozoi

c vo

lcan

o-se

dim

enta

ry c

ompl

exes

: A—

Rot

hste

in F

orm

atio

n; B

—A

ltenf

eld

Form

atio

n; C

—Fr

ohnb

erg

For-

mat

ion;

D—

Cla

nzsc

hwitz

Gro

up; E

—R

öder

n G

roup

; F—

Wee

sens

tein

Gro

up; G

—L

eipz

ig F

orm

atio

n; H

—L

ausi

tz G

roup

. Sam

ple

loca

tions

(sm

all t

ype

in s

tars

): a

—sa

mpl

e Pu

r-1

(Pur

purb

erg

quar

tzite

of

the

Wee

sens

tein

Gro

up, N

eopr

oter

ozoi

c);

b—W

ett-

1 (m

icro

cong

lom

erat

e of

the

Lau

sitz

Gro

up, N

eopr

oter

ozoi

c);

c—R

oth-

1–16

41H

/18

(gra

ywac

ke o

f th

e R

oths

tein

For

mat

ion,

N

eopr

oter

ozoi

c); d

—K

am-1

–120

9/1

(san

dsto

ne o

f th

e Z

wet

hau

Form

atio

n, L

ower

Cam

bria

n); e

—L

bq-1

(m

icro

cong

lom

erat

e, L

ange

r B

erg

Form

atio

n, T

rem

adoc

, Low

er O

rdov

icia

n).

66 Linneman et al.

spe423-03 page 66

488 Ma

Neo

pro

tero

zoic

(Ed

iaca

ran

)C

amb

rian

Low

erO

rdov

icia

n

datedsubvolcanicintrusion

dated detritalzircon

datedgranitoidpebble

dated tuff

LeipzigFormation

Schildaumassif

NorthSaxon

antiform(Leipzig)

530+/-8

LausitzGroup

Lausitzgranitoidcomplex

Lausitzantiform

Rumburkgranite

noOrdoviciansediments

490+/-3

539+/-6

RothsteinFormation

Torgau-Doberlugsyncline

566+/-10

589+/-9

AltenfeldFormation

Milchberggranite

Vessercomplex

Sc r -hwa zurb g

nti o ma f r(NW t)-Par

Dohnagranodiorite

Elbezone

Tourmalinegranite

FrohnbergFormation

Glasbach& Laubachgranites

w z urSc a b gh ra i ont f rm

Pa )(SE- rt

Blambachrhyolite

479+

/-2

487+/-6

533+/-4541+/-7

605+/-4

483+/-3

569+/-2

570+/-4

629+/-4

485+/-6

486+

/-4

537+/-7

Laasgranodiorite

NorthSaxon

antiform(Clanzschwitz)

531+/-7

Cadomianbackarc basin (N)

Cadomianbackarc basin (S)

External domain

Parautochthonous part of the Saxo-Thuringian zoneInternal domain

Cadomian retroarc basin

Strike-slipand spreadingzones in the

backarc basinon thinned

continental crust

WeesensteinGroup

568+/-4

ClanzschwitzGroup

577+/-3

Passive margin of the backarc basin on

thinned cratoniccrust and remnants

of an older Cadomian magmatic arc

Upper section (~100m):

remnant basinof the retroarc

against thepassive margin

& cratonic crust

1

1

44

22

2 2

2

2

2 2

2

2

2

3

222

2

2

2

L

MU

109521 3 4 6 7 8

502+/-2

Cd

ge

rc

ao

mia

nO

ron

yse

nsu

sti

to(

fe

he

/d

eo

rmat

ion

clo

sto

tP

rec.

Cam

b.-

un

yg

ai

nc

aB

od

ar,m

am

tc

eve

tat

.540

M)

Cad

om

ian

bas

emen

tse

nu

stri

cto

542 Ma

relativepaleo-position:

North

relativepaleo-position:

South

Pur-1

Wett-1

Roth-1577+/-10

555+/-9551+/-8

?

Proximate part ofthe retroarc basin

against the magmatic arc

Lower section:part of the distalretroarc basin

against the magmatic arc

*

*

Figure 3. Generalized lithostratigraphic profi les of parautochthonous units of the Saxo-Thuringian zone, with published geochronological data of the Cadomian basement and its Cambro-Ordovician overstep sequence. Circles designated “Roth-1”, “Wett-1” and “Pur-1” indicate position of samples studied in this article. 1—Cambro-Ordovician rift-related igneous rocks; 2—Cadomian granitoids of the ca. 540-Ma magmatic event; 3—Lower Ordovician siliciclastic sediments; 4—Late Neoproterozoic debris fl ows and glaciomarine tillites; 5—igneous rocks and metasedi-ments of the Upper Cambrian Vesser complex (predominantly mafi c rocks); 6—Neoproterozoic hydrothermal black cherts; 7—Lower to Middle Cambrian sediments; 8—conglomerates, quartzites, and quartzitic shales of the Purpurberg quartzite (Weesenstein Group) and its equivalent in the Clanzschwitz Group; 9—graywackes and mudstones; 10—predominantly mudstones. Sources of geochronological data (numbered circles): 1—SHRIMP U-Pb (Buschmann et al., 2001); 2—thermal ionization mass spectrometer (TIMS) Pb-Pb (Linnemann et al., 2000); 3—TIMS U-Pb (Kemnitz et al., 2002); 4—SHRIMP U-Pb (Linnemann et al., 2004).


spe423-03 page 67

B

D

E

C

A

Figure 4. Photographs of Cadomian basement rocks of the Saxo-Thuringian zone (Bohemian Massif). (A) Bedded black cherts of the “Rothstein Rock” near Bad Liebenwerda, which are interpreted to have formed close to the spreading center of the Cadomian back-arc basin (Neoproterozoic, ca. 570 Ma, Rothstein Formation, Cadomian basement of the Torgau-Doberlug syncline). (B) Steeply dipping bed of the Purpurberg quartzite with internal cross bedding and impressions of wave ripples (left freestanding bedding plane of block above hammer). The quartzite occurs in the lower part of the Weesenstein Group, which is interpreted to represent the passive margin of the Cadomian backarc basin (Neoproterozoic, ca. 570 Ma, Weesenstein Group, Purpurberg near Niederseidewitz, Cadomian basement of the Elbe zone). (C) Stretched granitoid pebble in a mudstone matrix derived from an eroded magmatic arc during the formation of the Cadomian back-arc basin (upper part of the Weesenstein Group). The pebbly mudstone facies of the Weesenstein Group is interpreted to be in part glaciomarine (Neoproterozoic, ca. 570 Ma, Weesenstein Group, 100 m east of the Weesenstein railway station, Cadomian basement of the Elbe zone). (D) Microconglomerate of the Lausitz Group containing clasts of cherts and felsic rocks. This sediment demonstrates the redeposition of black cherts and arc volcanics during the formation of the Cadomian retroarc basin (Neoproterozoic, ca. 570–545 Ma, Lausitz group, Petershain near Kamenz, Cadomian basement of the Lausitz anticline). (E) Water escape structure at top of the a-interval of a graywacke turbidite of the Lausitz Group, demonstrating rapid sedimentation in the Cadomian retroarc basin (Neopro-terozoic, ca. 570–545 Ma, Lausitz Group, Wetterberg quarry near Ebersbach, Cadomian basement of the Lausitz anticline).

68 Linneman et al.

spe423-03 page 68

The internal domain of the Saxo-Thuringian zone contains Cadomian rock units from two different depositional settings (Fig. 3). Voluminous Cadomian plutons intruded at ca. 540–530 Ma, and a thick and widely distributed Ordovician overstep sequence (Fig. 6) also distinguish the internal domain. Cambrian deposits are restricted to the Heinersdorf 1 and 2 drill holes in the Berga antiform and to large olistolithes in a Lower Carboniferous wild fl ysch matrix in the Görlitz synform.

The fi rst group of Neoproterozoic sedimentary units in the internal domain comprises passive margin sequences character-ized by highly mature quartzites, sandstones, and quartz-rich shales deposited in a shallow marine environment (Linnemann, 1991). The most prominent deposit of this type is represented by the Purpurberg quartzite in the lower part of the Weesenstein Group (Fig. 4B). Facies analysis of the Purpurberg quartzite has shown that its deposition was caused by an extreme drop of sea level that is interpreted to be of glacioeustatic origin (Linnemann, 1991). The stratigraphic equivalent of the Purpurberg quartzite also occurs in the Clanzschwitz Group (North Saxon antiform). Other parts of the Weesenstein and Clanzschwitz groups are like-wise passive margin deposits but comprise quartz-rich mud- and siltstones. In the upper part of the two groups diamictites and lay-ers with isolated pebbles (Fig. 4C) may be glaciomarine in origin (Linnemann and Romer, 2002). These passive margin deposits are situated in the North Saxon antiform and the Elbe zone (Fig. 2). Based on the spatial arrangement of the passive margin deposits in the Saxo-Thuringian zone, we assign these units to the pas-sive margin of the same Cadomian back-arc basin in which the Rothstein and the Altenfeld formations were deposited. Detrital zircons and dated pebbles point to a minimum age of sedimenta-tion of ca. 570 Ma for the passive margin units (Linnemann et al., 2000; Fig. 3).

The second group of Neoproterozoic sedimentary units in the internal domain is represented by the Lausitz Group (Lausitz antiform), the Leipzig Formation (Northsaxon antiform), and the Frohnberg Formation (southeastern part of the Schwarzburg anti-form). All three units are characterized by monotonous, fl ysch-like sections of proximal to distal dark-gray to black colored tur-bidites composed of graywacke and mudstone couplets (Fig. 4E). Seismites indicate an active tectonic setting during basin forma-tion. Intercalations of conglomerates contain fragments of black cherts (Fig. 4D) and other debris from older Neoproterozoic sedi-ments and igneous rocks. The pervasive occurrence of fragments of black chert in both the graywackes and the conglomerates suggests that deposits from the Cadomian back-arc basin of the external zone became eroded, recycled, and redeposited in the Cadomian retroarc basin, remnants of which are represented by the Lausitz Group and the Leipzig and the Frohnberg formations. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb dat-ing of detrital zircon grains in the Lausitz Group and the Frohn-berg Formation indicates that they are younger than 555 ± 9 Ma and 551 ± 8 Ma, respectively (Linnemann et al., 2004). Because of the occurrence of debris derived from the back-arc basin, the presence of distinct sedimentary features (see below), and their

?

?

?

?

?

?

?

?

?

?

siliciclasticdebris flows

limestone

no record

dolostone

claystone mafic volcanics

siltstone

sandstone

Zwet

hau

Form

atio

n

Low

erC

ambr

ian

Mid

dle

Cam

bria

nTr

öbitz

Form

atio

nD

elitz

sch

Form

atio

n

Torg

auM

embe

r(>

500

m)

Ros

enfe

ldM

br.

(>30

0m

)D

I(>

126

m)

LS1/

63I(

>57

5m

) DIV

(>41

m)

Kam-1

Figure 5. Generalized lithostratigraphic profi le of Cambrian sediments of the Torgau-Doberlug syncline with stratigraphic position of sample Kam-1–1209/1. The Lower Cambrian profi le is documented in numer-ous drill cores, whereas the Middle Cambrian profi le is derived from reference profi les (boreholes D I, LS 1/63, D IV). The Lower to Middle Cambrian sediments in the column overlie the Rothstein Formation (Neoproterozoic). Mbr—member. From Buschmann et al. (2006).


spe423-03 page 69

00

10001000

2000

3000

(m)

m

UntererFrauen-bach-quartzite

Frauen-bach-Wechsel-lagerung

ObererFrauen-bach-quartzite

Dach-schieferFm.

Go

ldis

-th

alF

m.

hi

erat

Ph

yco

den

scef

Fo

rmio

nt

.hy

code

nqua

rzi

FmP Qua

rzit-

plat

ten

Mbr

.

Bre

iten-

berg

Mbr

.

Qu

arzi

tban

kM

emb

er

Griffel-schieferFm.

Leder-schieferFm.

gap and/orcondensed

sedimentation

Schmie-defeld Fm.

rau

enG

r.F

bac

hc

eu

ho

sG

pP

yd

rore

ac

Tm

do

ent

alG

.G

räf

hi

shA

gll

Aren

ig

Conglomeratic tuffite(”Konglomeratische Arkose”)and yellow tuffites

topmost Neoproteroz. QuartziteCadomian basement:Cadomian basement:

Frohnberg Group (Neoprot.)Altenfeld Group (Neoproterozoic)black cherts

Glasbach granite (538+/-4 Ma*1)Milchberg granite

Lower Magnetite quartzite

Upper Magnetite quartzite

Lower ore horizon

Phycodes quartzite

Phycodes shale

Lower Frauenbach quartzite

interbedding of shaleand quartzite beds

Upper Frauenbach quartzite

“Phycodes Dachschiefer”

Upper ore horizon“Kalkbank” (limestone layer)Banded Lederschiefer

glaciomarine diamictiteof the Sahara glaciation= Lederschiefer

gapgapgap

no outcrop

gap

Bärentiegel porphyroid(479 +/-5 Ma*1)

Middle ore horizon

Blambach rhyolite (487+/-5 Ma*1)

Dacitic pyroclastite508+/-2 Ma *2

Gabbro502+/-2 Ma *2

Ros

en-

berg

Mbr

.G

öri

tzb

erg

Mem

ber

Lau

sch

enst

ein

Mem

ber

i sG ller dorf Fm.

Neu

wer

kF

m.

Volc

anic

un

itQ

uar

tzit

eu

nit

Ro

llko

pf

Fo

r mat

i on

Hu

nd

srü

ckG

.V

e ss e

rG

rou

p

low

e ru

pp

er

Cadomianbasement

Ord

ovi

cian

Trem

ado

cU

pp

erC

amb

rian

Mid

dle

Cam

br .

dark shales

KArc-1

1

2

4

6

7

10

11

12

9

8

5

3

Lbq-1

Ves-1

?

La er Be .ng rg Fm

Ves

ser

com

ple

x

NW-part of theSchwarzburg

antiformVesser

complex

SE-part of the Schwarzburg antiform

Figure 6. Lithostratigraphic profi les of the Middle and Upper Cambrian and Ordovician rocks of the Vesser complex and the northwestern and southeastern parts of the Schwarzburg antiform. Ellipses Ves-1, Lbq-1, and KArc-1 indicate approximate position of samples studied in this article. 1—Upper Cambrian Rollkopf Formation of the Vesser complex: predominantly mafi c subvolcanic rocks (tholeiitic dolerites and gabbros) and minor subalkaline basalts, dacitic tuffs, rhyolitic ignimbrites, granites, and graphitic metasediments; 2—Upper Cambrian Neu-werk Formation of the Vesser complex: interbedded tholeiitic basaltic, dacitic to trachyandesitic lavas and intermediate to rhyolitic pyroclastics and metasediments; 3—Tremadocian volcanic unit of the Hundsrück Group in the Vesser complex: rhyolitic pyroclastic rocks, and arkoses; 4—rhyolites and porphyroids; 5—Cadomian granites; 6—Neoproterozoic sediments (predominantly graywacke turbidites); 7—conglomerates, microconglomerates, and conglomeratic tuffi tes; 8—sandstones and quartzites; 9—mudstones and silty shales; 10—shales; 11—diamictite (gla-ciomarine tillite?); 12—sedimentary iron ores. Fm—formation; G—group; Mbr—member. Sources of geochronological data: *1—TIMS Pb-Pb (Linnemann et al., 2000); *2—TIMS U-Pb (Kemnitz et al., 2002). Modifi ed after Bankwitz et al. (1992), Linnemann (1996), Linnemann and Heuse (2000), and Kemnitz et al. (2002).

70 Linneman et al.

spe423-03 page 70

maximum ages of sedimentation between ca. 555 and 551 Ma, we classify the Lausitz Group and the Leipzig and Frohnberg formations as relicts of a Cadomian retroarc basin.

In general, all Neoproterozoic sections within the Cado-mian basement of the Saxo-Thuringian zone seem to be rootless because of Variscan stacking of the crust, and an underlying cra-tonic basement is not known. However, Neodymium depleted-mantle (NdT

DM) model ages for the Late Neoproterozoic sedi-

ments range between 1.9 and 1.3 Ga (Linnemann and Romer, 2002), clearly indicating that the source area of the Neoprotero-zoic sediments was dominated by old cratonic crust.

With exception of the Rothstein Formation and maybe the Altenfeld Formation, all Neoproterozoic sedimentary sequences within the Cadomian basement in the Saxo-Thuringian zone were intruded by Early Cambrian post-kinematic granitoid plu-tons in the interval ca. 540–530 Ma (Linnemann et al. 2000; Gehmlich 2003; Tichomirowa, 2003). These plutonic suites are composed of granites, syeno- and monzogranites, granodiorites, and tonalites (Hammer, 1996), whereas granodiorites dominate in most plutons.

The Cadomian basement of the Saxo-Thuringian zone is overlain, usually unconformably, by Lower Paleozoic sedi-ments. Transgression and the development of Lower to Middle Cambrian overstep sequences—including the deposition of con-glomerates, carbonates, siliciclastics, and red beds, with a dep-ositional gap in the lowermost Cambrian (ca. 540–530 Ma)— characterize the fi rst post-Cadomian sedimentary sequence. A second widely distributed gap in sedimentation occurred in the Upper Cambrian (ca. 500–490 Ma), although the Vesser com-plex is composed of mid- to Upper Cambrian magmatic rocks and metasediments related to an oceanic setting (Bankwitz et al., 1992; Kemnitz et al., 2002).

Special features—such as the occurrence of a Cadomian unconformity; peri-Gondwanan Cambro-Ordovician faunas; gla-ciomarine diamictites of the Hirnantian glaciation in the upper-most Ordovician; and the absence of any Salinic, Acadian, and Caledonian orogenic infl uences—paleogeographically link the Saxo-Thuringian zone to Gondwana in the Neoproterozoic and Lower Paleozoic (Linnemann et al., 2000, 2004).

SAMPLES AND METHODS

For provenance studies, detrital zircons were collected from three Neoproterozoic siliciclastic sedimentary rock units, which were deposited in three distinct settings of Cadomian basin devel-opment. Sample Pur-1 was taken from the Purpurberg quartzite of the Weesenstein Group in the Elbe zone. This sediment was deposited in a passive continental margin setting of the Cado-mian back-arc basin distal from the arc. Sample Roth-1 is a gray-wacke of the Rothstein Formation in the Torgau-Doberlug syn-cline taken from the drill hole WisBaW 1641H/80 near the city of Herzberg. Sediments of the Rothstein Formation were deposited in the Cadomian back-arc basin proximal to the arc on the oppo-site side to that of the passive margin.

The third Neoproterozoic sample is a chert-bearing micro-conglomerate (Wett-1) of the Lausitz Group from the Lausitz antiform. This sample was collected from the Wetterberg quarry near the village of Ebersbach. The Lausitz Group is dominated by graywacke turbidites with intercalations of microconglomer-ates deposited in the Cadomian retroarc basin or foreland basin.

In addition, a Lower Cambrian sandstone (Kam-1) and an Ordovician microconglomerate (Lbq-1) were sampled from the Saxo-Thuringian zone. These samples represent Cambro-Ordo-vician shelf sediments, which overlie the Cadomian basement. Kam-1 was taken from a drill core of the Zwethau Formation in the Torgau-Doberlug syncline. The sample was collected from drill hole WisBaW 1209/78 near the village of Falkenberg and is representative of the Lower Cambrian overstep sequence overly-ing the deformed Cadomian sediments of the Rothstein Forma-tion. The Lower to Middle Cambrian sediments of this formation were deposited in an asymmetric rift basin. Lbq-1 is a Lower Ordovician microconglomerate sampled from the Langer Berg Formation close to the village of Willmersdorf in the northwest-ern part of the Schwarzburg antiform. The Langer Berg Formation is a section of highly mature quartzites and conglomerates typi-cal of the widely distributed Lower Ordovician shallow marine sedimentation of the Gondwanan realm. The Lower Ordovician overstep sequence in the Saxo-Thuringian zone was deposited in a rifted shelf basin in a passive margin setting.

To set additional lithostratigraphic time markers for the Cam-brian and Ordovician sedimentation, an Upper Cambrian ignim-brite (Ves-1) and a Lower Ordovician tuffi te (KArc-1) were sam-pled. Sample Ves-1 was taken from a rhyolitic ignimbrite from the Vesser complex (Fig. 6). Sample KArc-1, a pebble-bearing rhyolitic tuffi te, was collected in the valley of the Blambach close to Sitzendorf, from the base of the >3000-m-thick Ordovician sedimentary succession exposed in the southeastern part of the Schwarzburg antiform. This pyroclastic sediment is referred to in traditional German literature as “Konglomeratische Arkose” (=conglomeratic arkose). Additional information concerning the lithostratigraphy and coordinates of the sample locations is given in Tables 1, 2, and 3.

Zircon concentrates were separated at the Museum für Mineralogie und Geologie (Staatliche Naturhistorische Samm-lungen Dresden). Fresh samples were crushed in a jaw crusher and sieved for the fraction 63–400 μm. Density separation of this fraction by a heavy liquid was realized using sodium heteropoly-tungstate in water (“LST fast fl oat”) and followed by magnetic separation of the extracted heavy minerals in a Frantz isodynamic separator. Final selection of the zircon grains for U-Pb dating was achieved by hand-picking under a binocular microscope. Zircon grains of all grain sizes and morphological types were selected, mounted in resin blocks, and polished to half their thickness.

Zircons were analyzed for U, Th, and Pb isotopes by LA-ICP-MS techniques at the Institute of Geosciences, Johann Wolf-gang Goethe-University Frankfurt, using a Thermo-Finnigan Ele-ment II™ sector fi eld ICP-MS coupled to a New Wave™ UP-213 ultraviolet laser system. A teardrop-shaped, low-volume laser cell


spe423-03 page 71

TAB

LE 1

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

NE

OP

RO

TE

RO

ZO

IC Q

UA

RZ

ITE

S O

F T

HE

ELB

EZ

ON

E,

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ %R

ho**

207 P

b23

5 U±

2σ(M

a)

206 P

b23

8 U±

2σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Pur

-1 (

Loca

tion:

Pur

purb

erg

quar

tzite

, Neo

prot

eroz

oic,

Edi

caria

n, W

eese

ntei

n gr

oup,

Elb

e zo

ne, P

urpu

rber

g ne

ar O

bers

eide

witz

, Eas

ting:

42

3117

, Nor

thin

g: 5

6 40

750)

P-L

10-1

5820

160

640.

310.

3770

0.9

6.96

61.

40.

1340

1.1

0.62

2107

2520

6231

2151

3996

P-L

10-2

2614

868

128

40.

440.

3820

0.8

6.77

51.

00.

1287

0.6

0.81

2083

1720

8528

2080

2010

0P

-L10

-363

2420

699

1.85

0.30

911.

05.

406

1.3

0.12

680.

90.

7118

8623

1736

2920

5434

85P

-L10

-410

2423

125

0.72

0.09

570.

90.

7893

2.2

0.05

982.

00.

4159

120

589

1059

888

99P

-L10

-537

2396

461.

150.

3739

0.9

6.43

31.

60.

1248

1.2

0.61

2037

2720

4733

2026

4410

1P

-L10

-618

901

857

197

0.13

0.22

811.

03.

704

1.1

0.11

780.

60.

8515

7218

1325

2319

2221

69P

-L10

-710

3373

141.

400.

1293

1.3

2.30

53.

20.

1293

2.9

0.42

1214

4678

420

2088

103

38P

-L10

-895

873

101.

070.

1167

1.0

1.04

12.

70.

0647

2.5

0.38

725

2971

214

765

107

93P

-L10

-918

098

145

101

0.26

0.60

111.

022

.33

1.3

0.26

940.

90.

7331

9826

3034

4733

0229

92P

-L10

-10

3941

840

519

40.

470.

3566

1.0

13.3

81.

70.

2721

1.3

0.62

2707

3219

6635

3318

4159

P-L

10-1

111

1424

825

0.58

0.09

251.

00.

7705

2.1

0.06

041.

80.

4958

018

571

1161

778

92P

-L10

-12

9860

182

211.

150.

0925

1.1

0.74

861.

70.

0587

1.4

0.62

567

1557

012

555

6010

3P

-L10

-13

1504

922

214

01.

010.

4907

0.9

11.8

51.

10.

1751

0.7

0.80

2592

2125

7439

2607

2399

P-L

10-1

417

3917

017

0.67

0.09

241.

00.

7566

2.1

0.05

941.

90.

4757

219

570

1158

181

98P

-L10

-15

1010

668

0.93

0.09

811.

20.

8093

2.4

0.05

982.

10.

5160

222

603

1459

791

101

P-L

10-1

627

258

174

141

0.51

0.64

810.

826

.72

1.0

0.29

910.

70.

7833

7320

3221

4134

6520

93P

-L10

-17

4213

6035

0.62

0.49

181.

112

.25

1.6

0.18

071.

20.

6626

2430

2578

4526

5940

97P

-L10

-18

1704

2411

0.92

0.40

041.

77.

900

2.5

0.14

311.

80.

6822

2046

2171

6422

6564

96P

-L10

-19

5850

162

670.

680.

3513

0.9

6.09

81.

40.

1259

1.1

0.61

1990

2519

4129

2041

4095

P-L

10-2

019

3425

928

0.86

0.09

260.

80.

7673

2.1

0.06

011.

90.

3857

819

571

960

884

94P

-L10

-21

5516

9747

0.98

0.34

090.

85.

642

2.7

0.12

002.

60.

2919

2247

1891

2619

5791

97P

-L10

-22

4759

6244

1.38

0.50

831.

113

.00

1.5

0.18

561.

10.

7026

8029

2649

4627

0336

98P

-L10

-23

7390

8253

0.51

0.55

051.

014

.87

1.5

0.19

591.

10.

6528

0728

2827

4427

9237

101

P-L

10-2

417

0224

827

0.75

0.09

701.

00.

7922

2.0

0.05

921.

80.

4959

218

597

1157

678

104

P-L

10-2

557

171

371

322

0.82

0.65

310.

926

.09

1.0

0.28

980.

40.

9033

5020

3240

4634

1613

95P

-L10

-26

2487

216

913

90.

460.

6679

1.1

26.3

61.

40.

2863

0.7

0.84

3360

2732

9859

3398

2397

P-L

10-2

712

4319

721

0.32

0.09

191.

40.

7537

2.5

0.05

952.

00.

5657

022

567

1558

588

97P

-L10

-28

1118

221

270.

560.

1005

1.6

0.82

802.

50.

0597

1.9

0.63

613

2361

719

595

8410

4P

-L10

-29

2173

369

632.

080.

0979

1.4

0.81

561.

70.

0604

1.1

0.79

606

1660

216

618

4697

P-L

10-3

016

7929

648

1.50

0.10

331.

20.

8878

2.0

0.06

231.

50.

6264

519

634

1568

665

92P

-L10

-31

1506

6024

0.68

0.31

341.

74.

730

2.3

0.10

941.

50.

7517

7339

1758

5317

9055

98P

-L10

-32

3245

9641

0.63

0.33

211.

25.

350

1.6

0.11

681.

00.

7518

7727

1849

3819

0837

97P

-L10

-33

988

7513

1.69

0.10

111.

20.

8390

2.6

0.06

022.

30.

4761

924

621

1461

099

102

P-L

10-3

589

817

420

0.43

0.09

611.

70.

8117

3.3

0.06

132.

80.

5360

330

592

2064

812

191

P-L

10-3

632

2744

459

0.86

0.10

361.

20.

8752

1.8

0.06

131.

30.

6663

817

635

1464

958

98P

-L10

-37

3112

415

520.

440.

1064

1.1

0.92

522.

10.

0631

1.8

0.52

665

2165

214

710

7792

P-L

10-3

812

438

267

121

0.43

0.36

371.

26.

371

1.5

0.12

700.

90.

8220

2827

2000

4320

5731

97P

-L10

-39

1015

8113

0.90

0.09

951.

40.

8480

2.6

0.06

182.

10.

5762

424

612

1766

790

92P

-L10

-40

1235

4318

1.05

0.33

011.

55.

319

2.5

0.11

692.

00.

5918

7243

1839

4719

0971

96P

-L10

-41

683

123

150.

470.

0997

1.2

0.83

892.

00.

0610

1.7

0.58

619

1961

214

641

7196

Con

tinue

d

72 Linneman et al.

spe423-03 page 72

TAB

LE 1

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

NE

OP

RO

TE

RO

ZO

IC Q

UA

RZ

ITE

S O

F T

HE

ELB

EZ

ON

E,

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

(co

ntin

ued)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ %R

ho**

207 P

b23

5 U±

2σ(M

a)

206 P

b23

8 U±

2σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Pur

-1 (

cont

inue

d)

P-L

10-4

216

1631

233

0.23

0.09

351.

10.

7746

1.7

0.06

011.

40.

6358

216

576

1260

758

95P

-L10

-43

5059

6540

0.37

0.48

321.

111

.40

1.5

0.17

110.

90.

7725

5728

2541

4825

6932

99P

-L10

-44

1543

8719

3.06

0.10

421.

50.

8843

2.9

0.06

162.

50.

5164

328

639

1865

910

697

P-L

10-4

512

0175

100.

640.

0992

1.5

0.84

003.

00.

0614

2.6

0.49

619

2860

917

655

113

93P

-L10

-46

1277

9712

0.58

0.10

171.

40.

8696

2.4

0.06

202.

00.

5663

523

624

1667

587

93P

-L10

-47

1250

112

131

0.45

0.14

591.

81.

426

2.2

0.07

091.

30.

8190

027

878

3095

453

92P

-L10

-48

1460

133

290.

920.

1626

1.2

1.64

21.

80.

0733

1.4

0.63

987

2397

121

1021

5895

P-L

10-4

930

561

178

168

0.59

0.66

041.

225

.14

1.5

0.27

600.

90.

8133

1429

3269

6133

4127

98P

-L10

-50

1147

150

200.

600.

1049

1.4

0.88

232.

40.

0610

2.0

0.57

642

2364

317

639

8510

1P

-L10

-51

3728

9150

1.22

0.37

441.

16.

417

1.6

0.12

431.

10.

7120

3529

2050

4020

1940

102

P-L

10-5

210

6828

130.

770.

3359

1.3

5.50

41.

80.

1189

1.2

0.73

1901

3118

6743

1939

4496

P-L

10-5

310

912

303

108

0.45

0.32

661.

35.

258

1.6

0.11

680.

90.

8118

6227

1822

4119

0733

96P

-L10

-54

9971

284

980.

450.

3167

1.4

5.07

21.

70.

1161

1.0

0.82

1832

3017

7444

1898

3593

P-L

10-5

521

3662

240.

690.

3370

1.5

5.49

62.

10.

1183

1.4

0.72

1900

3618

7248

1931

5197

P-L

10-5

614

5351

70.

590.

1296

1.4

1.17

92.

80.

0660

2.4

0.51

791

3178

621

805

101

98P

-L10

-57

8669

170

800.

680.

4035

1.4

7.45

91.

60.

1341

0.9

0.85

2168

3021

8552

2152

3010

2P

-L10

-58

5387

110

440.

370.

3636

1.5

6.51

82.

70.

1300

2.2

0.57

2048

4819

9953

2098

7895

P-L

10-5

913

890

286

118

0.46

0.36

851.

46.

955

1.6

0.13

690.

70.

9021

0628

2022

4921

8824

92P

-L10

-60

999

9810

0.38

0.09

521.

40.

7844

2.9

0.05

972.

60.

4858

826

586

1659

411

199

P-L

10-6

121

756

413

157

0.98

0.31

003.

36.

783

3.4

0.15

870.

90.

9620

8462

1741

101

2442

3271

P-L

10-6

211

9224

225

0.56

0.09

571.

30.

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0.05

972.

00.

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022

589

1559

488

99P

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-63

1300

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011.

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634

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00.

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1935

5619

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102

P-L

10-6

410

484

251

124

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591.

46.

155

1.5

0.12

200.

70.

8819

9827

2010

4719

8626

101

P-L

10-6

598

921

620

0.36

0.09

041.

50.

7364

2.8

0.05

912.

40.

5256

024

558

1657

010

598

P-L

10-6

679

3372

561.

060.

5863

1.3

17.1

51.

50.

2122

0.8

0.85

2943

3029

7463

2922

2610

2P

-L10

-67

5692

107

470.

390.

3871

1.8

8.61

22.

40.

1614

1.6

0.75

2298

4421

0964

2470

5385

P-L

10-6

813

9623

025

0.79

0.09

811.

50.

8144

2.7

0.06

022.

30.

5460

525

603

1761

198

99P

-L10

-69

3073

7333

0.81

0.37

141.

36.

529

2.0

0.12

751.

50.

6620

5035

2036

4620

6453

99P

-L10

-70

5608

6840

0.54

0.51

891.

413

.46

1.8

0.18

821.

00.

8227

1333

2695

6327

2633

99P

-L10

-71

1230

859

0.04

0.11

012.

00.

9314

8.4

0.06

148.

20.

2366

884

673

2565

235

310

3P

-L10

-74

4643

168

860.

340.

4687

1.3

11.0

11.

60.

1704

0.9

0.81

2524

3024

7854

2561

3297

P-L

10-7

641

824

386

247

0.43

0.55

231.

616

.19

1.6

0.21

270.

40.

9628

8831

2835

7229

2614

97P

-L10

-77

3440

533

610.

550.

1040

1.5

0.89

291.

80.

0623

1.1

0.81

648

1763

818

683

4693

P-L

10-7

846

7510

549

0.71

0.39

111.

47.

344

1.8

0.13

621.

10.

8021

5432

2128

5221

7937

98

Wet

t-1

(Loc

atio

n: m

icro

cong

lom

erat

e, N

eopr

oter

ozoi

c, E

diac

aria

n, L

ausi

tz g

roup

, Lau

sitz

ant

iform

, Wet

terb

erg

near

Ebe

rsba

ch, E

astin

g: 4

0 52

84, N

orth

ing:

56

8022

6)

W-s

1-u1

3134

698

0.41

0.10

510.

70.

8834

1.3

0.06

101.

10.

5564

312

644

963

846

101

W-s

1-u2

6397

159

160.

440.

0956

0.7

0.77

711.

20.

0589

1.0

0.54

584

1158

98

565

4610

4W

-s1-

u362

6415

713

0.18

0.08

780.

60.

7057

1.3

0.05

831.

20.

4654

211

542

654

251

100

W-s

1-u4

5911

100

110.

620.

0959

0.7

0.78

511.

60.

0594

1.5

0.44

588

1459

08

580

6310

2W

-s1-

u511

710

255

280.

420.

1051

0.6

0.87

741.

00.

0605

0.9

0.57

640

1064

47

622

3710

4W

-s1-

u612

003

281

300.

530.

0997

0.6

0.81

621.

00.

0594

0.8

0.58

606

961

37

581

3610

5W

-s1-

u795

089

108

580.

130.

4985

0.6

13.7

80.

90.

2004

0.6

0.71

2734

1626

0726

2830

2092

Con

tinue

d


spe423-03 page 73

TAB

LE 1

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

NE

OP

RO

TE

RO

ZO

IC Q

UA

RZ

ITE

S O

F T

HE

ELB

EZ

ON

E,

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

(co

ntin

ued)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ %R

ho**

207 P

b23

5 U±

2σ(M

a)

206 P

b23

8 U±

2σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Wet

t-1

(con

tinue

d)

W-s

1-u7

c19

5089

309

214

0.35

0.60

991.

620

.97

1.8

0.24

940.

90.

8831

3736

3070

7831

8127

96W

-s1-

u817

962

376

460.

860.

1013

0.7

0.85

431.

00.

0611

0.6

0.75

627

962

29

644

2797

W-s

1-u9

8833

199

210.

460.

0966

0.6

0.78

511.

00.

0589

0.8

0.57

588

959

56

565

3510

5W

-s1-

u10

1056

522

424

0.38

0.10

120.

70.

8557

1.1

0.06

130.

90.

6262

810

621

865

137

95W

-s1-

u11

2635

294

370.

790.

3309

0.8

5.22

81.

00.

1146

0.6

0.81

1857

1618

4325

1873

2098

W-s

1-u1

234

944

120

440.

350.

3450

0.7

5.51

90.

90.

1160

0.5

0.84

1904

1519

1025

1896

1710

1W

-s1-

u13

7051

425

596

0.65

0.32

750.

65.

089

0.8

0.11

270.

50.

8018

3414

1826

2018

4317

99W

-s1-

u14

1860

541

143

0.56

0.09

600.

80.

7817

1.0

0.05

910.

60.

7858

69

591

957

028

104

W-s

1-u1

519

303

263

450.

430.

1627

0.8

1.60

81.

10.

0717

0.7

0.78

973

1397

215

976

2710

0W

-s1-

u16

2891

6639

822

90.

240.

5290

0.6

13.4

00.

70.

1838

0.3

0.86

2708

1327

3726

2687

1110

2W

-s1-

u17

1954

280

280.

670.

2945

1.0

4.53

01.

20.

1116

0.6

0.84

1736

2016

6429

1825

2391

W-s

1-u1

840

604

6135

0.72

0.47

170.

611

.46

0.8

0.17

620.

50.

7525

6114

2491

2426

1817

95W

-s1-

u19

4567

9212

0.64

0.11

690.

71.

0112

1.4

0.06

271.

30.

4870

915

713

969

954

102

W-s

1-u2

059

2214

315

0.52

0.09

610.

60.

7856

1.2

0.05

931.

00.

5358

911

591

757

944

102

W-s

1-u2

112

664

312

320.

490.

0956

0.6

0.77

831.

10.

0590

0.9

0.54

585

1058

97

568

4110

4W

-s1-

u22

3586

818

253

0.33

0.27

441.

24.

111

1.3

0.10

870.

50.

9116

5721

1563

3317

7720

88W

-s1-

u23

5172

115

766

0.58

0.36

730.

76.

174

0.9

0.12

190.

50.

8420

0116

2017

2619

8418

102

W-s

1-u2

425

772

6926

0.45

0.33

321.

25.

627

1.9

0.12

251.

40.

6619

2032

1854

4019

9250

93W

-s1-

u25

6473

148

211.

600.

0987

0.8

0.81

261.

20.

0597

0.9

0.66

604

1160

79

594

3910

2W

-s1-

u26

4103

610

6198

0.27

0.09

230.

80.

7495

0.9

0.05

890.

40.

9156

88

569

956

217

101

W-s

1-u2

714

934

267

350.

740.

1001

0.7

0.85

091.

00.

0617

0.7

0.74

625

961

59

663

2993

W-s

1-u2

835

2882

111.

580.

0956

0.6

0.79

551.

50.

0603

1.4

0.42

594

1458

97

616

6096

W-s

1-u2

929

962

8134

0.42

0.38

600.

86.

859

1.0

0.12

890.

60.

8020

9318

2104

2820

8321

101

W-s

1-u3

077

679

7458

1.12

0.56

870.

618

.01

0.7

0.22

970.

40.

8529

9014

2903

2930

5012

95W

-s2-

u31

1294

229

035

1.24

0.09

231.

10.

7625

1.3

0.05

990.

80.

7957

512

569

1160

036

95W

-s2-

u32

1482

051

210.

950.

3328

0.9

5.23

71.

30.

1141

0.9

0.72

1859

2218

5230

1866

3299

W-s

2-u3

326

0309

762

307

0.30

0.37

991.

06.

542

1.0

0.12

490.

40.

9320

5218

2076

3420

2713

102

W-s

2-u3

427

117

405

640.

490.

1498

0.8

1.41

41.

20.

0685

0.9

0.63

895

1590

013

883

3910

2W

-s2-

u35

1953

839

747

0.70

0.10

560.

90.

8925

1.2

0.06

130.

80.

7564

812

647

1165

035

100

W-s

2-u3

653

5463

110.

590.

1613

0.8

1.59

051.

20.

0715

0.9

0.68

966

1596

415

972

3699

W-s

2-u3

737

659

105

470.

840.

3629

0.8

6.35

40.

90.

1270

0.4

0.88

2026

1619

9627

2057

1597

W-s

2-u3

840

5674

90.

320.

1151

0.9

0.99

761.

50.

0628

1.2

0.57

703

1570

211

703

5210

0W

-s2-

u39

5770

140

140.

560.

0924

0.8

0.76

301.

30.

0599

1.0

0.63

576

1257

09

600

4595

W-s

2-u4

025

160

8236

1.03

0.35

060.

85.

626

1.0

0.11

640.

60.

8019

2018

1937

2819

0122

102

W-s

2-u4

161

665

8256

0.81

0.53

920.

914

.03

1.1

0.18

860.

60.

8527

5120

2780

4027

3018

102

W-s

2-u4

211

239

138

230.

440.

1537

1.1

1.45

61.

30.

0687

0.8

0.80

912

1692

218

890

3310

4W

-s2-

u43

1579

037

138

0.51

0.09

600.

90.

7963

1.1

0.06

020.

70.

7959

510

591

1060

930

97W

-s2-

u44

6575

148

180.

830.

1038

0.9

0.86

671.

40.

0606

1.1

0.62

634

1363

711

624

4810

2W

-s2-

u45

3595

514

752

0.56

0.31

940.

94.

725

1.1

0.10

730.

70.

7517

7219

1787

2717

5427

102

W-s

2-u4

620

520

5226

0.92

0.39

200.

97.

314

1.2

0.13

530.

70.

7921

5121

2132

3321

6824

98W

-s2-

u47

8530

201

200.

670.

0884

0.9

0.72

061.

40.

0591

1.1

0.61

551

1254

69

571

4896

Con

tinue

d

74 Linneman et al.

spe423-03 page 74

TAB

LE 1

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

NE

OP

RO

TE

RO

ZO

IC Q

UA

RZ

ITE

S O

F T

HE

ELB

EZ

ON

E,

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

(co

ntin

ued)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ %R

ho**

207 P

b23

5 U±

2σ(M

a)

206 P

b23

8 U±

2σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Wet

t-1

(con

tinue

d)

W-s

2-u4

815

685

370

370.

540.

0936

1.0

0.76

741.

20.

0595

0.7

0.83

578

1057

711

585

2999

W-s

2-u4

931

4944

914

323

0.12

0.34

891.

16.

117

1.2

0.12

720.

30.

9619

9320

1929

3720

5912

94W

-s2-

u50

3838

798

0.52

0.08

750.

80.

7031

1.6

0.05

831.

40.

5154

113

541

854

060

100

W-s

2-u5

162

7712

414

0.67

0.10

290.

90.

8740

2.6

0.06

162.

40.

3463

824

631

1166

110

395

W-s

2-u5

268

9884

1239

498

0.16

0.37

071.

49.

602

1.8

0.18

791.

00.

8123

9733

2033

5027

2434

75W

-s2-

u53

6300

152

140.

350.

0878

0.8

0.70

391.

30.

0582

1.1

0.57

541

1154

28

536

4810

1W

-s2-

u54

3523

708

0.51

0.10

481.

00.

8761

1.8

0.06

071.

40.

5963

917

642

1362

762

102

W-s

2-u5

518

814

393

350.

140.

0932

1.0

0.76

011.

30.

0591

0.9

0.76

574

1257

511

572

3710

0W

-s2-

u56

4091

505

0.57

0.08

811.

10.

7016

1.8

0.05

781.

50.

5854

015

544

1152

166

104

W-s

2-u5

734

192

868

810.

350.

0923

1.0

0.74

661.

20.

0587

0.6

0.86

566

1056

911

555

2610

3W

-s2-

u58

1111

828

327

0.31

0.09

370.

80.

7631

1.1

0.05

910.

80.

7457

610

577

957

033

101

W-s

2-u5

954

8813

613

0.28

0.09

530.

90.

7819

1.7

0.05

951.

40.

5658

715

587

1058

559

100

W-s

2-u6

088

4319

924

0.86

0.10

271.

00.

8485

1.3

0.05

990.

90.

7262

417

630

1260

240

105

Rot

h-1

(Loc

atio

n: g

rayw

acke

, Neo

prot

eroz

ic, E

diac

aria

n, R

oths

tein

For

mat

ion,

Tor

gau-

Dob

erlu

g sy

nclin

e, d

rill W

isB

aW 1

641H

/80

near

Her

zber

g, d

epth

of s

ampl

ed c

ore:

507

.0 m

, E

astin

g: 3

8 39

04, N

orth

ing:

57

2741

9)

Rot

-129

1357

60.

550.

0917

1.0

0.74

161.

60.

0587

1.2

0.65

563

1456

511

555

5210

2R

ot-2

1339

133

840

0.93

0.10

111.

00.

8465

1.3

0.06

070.

80.

7962

312

621

1263

035

99R

ot-3

4375

112

120.

660.

0996

1.0

0.84

021.

30.

0612

0.9

0.75

619

1361

212

645

3895

Rot

-456

9015

115

0.43

0.09

671.

10.

8132

1.4

0.06

100.

90.

7860

413

595

1263

937

93R

ot-5

2711

646

0.31

0.09

261.

20.

7511

2.0

0.05

881.

60.

6056

918

571

1356

171

102

Rot

-634

6197

90.

370.

0951

1.2

0.78

702.

10.

0600

1.7

0.59

589

1858

614

603

7297

Rot

-770

8719

522

0.83

0.09

861.

00.

8162

1.4

0.06

011.

00.

7160

613

606

1160

543

100

Rot

-846

2612

115

1.70

0.09

651.

00.

7967

1.5

0.05

991.

10.

6959

513

594

1159

946

99R

ot-9

7383

207

241.

520.

0929

1.0

0.76

431.

40.

0597

1.0

0.72

577

1357

311

592

4397

Rot

-10

2220

497

1.01

0.11

571.

41.

001

1.7

0.06

271.

00.

8270

417

706

1869

941

101

Rot

-11

1576

6759

323

30.

600.

3531

1.1

5.93

61.

20.

1219

0.4

0.93

1966

2019

4936

1985

1598

Rot

-12

5806

162

160.

580.

0912

1.0

0.73

701.

30.

0586

0.7

0.81

561

1156

311

552

3310

2R

ot-1

345

8812

214

0.90

0.09

941.

10.

8227

1.6

0.06

001.

20.

6961

015

611

1360

550

101

Rot

-14

3948

106

121.

030.

0922

1.0

0.75

001.

80.

0590

1.5

0.58

568

1656

811

567

6310

0R

ot-1

581

8439

140.

580.

3073

1.0

4.62

31.

50.

1091

1.0

0.72

1753

2517

2732

1785

3797

Rot

-16

1896

325

0.57

0.13

041.

11.

172

1.6

0.06

521.

20.

6778

718

790

1678

050

101

Rot

-17

4317

127

130.

610.

0942

1.2

0.76

992.

10.

0593

1.7

0.58

580

1858

013

577

7310

1R

ot-1

843

1712

713

0.61

0.09

431.

20.

7735

2.2

0.05

951.

80.

5558

220

581

1358

480

99R

ot-1

946

7713

314

0.46

0.09

911.

00.

8165

1.4

0.05

980.

90.

7460

613

609

1259

541

102

Rot

-20

1760

646

654

1.09

0.09

581.

10.

8061

1.4

0.06

100.

70.

8360

012

590

1363

932

92R

ot-2

154

1088

121.

030.

1045

1.0

0.87

661.

60.

0609

1.2

0.64

639

1564

112

634

5210

1R

ot-2

216

527

437

500.

830.

0992

1.1

0.83

201.

30.

0608

0.7

0.86

615

1261

013

634

2896

Rot

-23

3700

210

5910

70.

550.

0932

1.1

0.77

921.

20.

0606

0.5

0.92

585

1157

513

626

2192

Rot

-24

1812

389

290.

360.

3136

1.0

4.70

91.

20.

1089

0.7

0.83

1769

2117

5832

1781

2599

Rot

-25

6256

922

183

0.19

0.36

741.

06.

546

1.3

0.12

920.

80.

7920

5223

2017

3620

8828

97

Con

tinue

d


spe423-03 page 75

TAB

LE 1

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

NE

OP

RO

TE

RO

ZO

IC Q

UA

RZ

ITE

S O

F T

HE

ELB

EZ

ON

E,

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

(co

ntin

ued)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ %R

ho**

207 P

b23

5 U±

2σ(M

a)

206 P

b23

8 U±

2σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Rot

h-1

(con

tinue

d)

Rot

-26

3860

8511

1.18

0.11

131.

20.

9605

1.7

0.06

261.

20.

7168

417

680

1669

451

98R

ot-2

719

366

5931

1.34

0.38

471.

17.

280

1.2

0.13

720.

70.

8521

4622

2098

3821

9323

96R

ot-2

825

5959

70.

760.

1048

1.4

0.87

982.

30.

0609

1.8

0.60

641

2264

317

634

7910

1R

ot-2

910

046

219

280.

560.

1161

1.0

1.02

21.

30.

0638

0.9

0.76

715

1470

814

735

3696

Rot

-30

8780

231

250.

600.

0991

1.1

0.82

421.

40.

0603

0.9

0.78

610

1360

913

616

3899

Rot

-31

8396

131

213

60.

730.

3770

0.9

6.57

21.

00.

1264

0.5

0.87

2056

1820

6231

2049

1810

1R

ot-3

239

0248

462

283

0.15

0.55

420.

917

.585

1.0

0.23

020.

30.

9629

6719

2842

4330

539

93R

ot-3

332

8154

70.

410.

1218

1.3

1.08

821.

80.

0648

1.2

0.72

748

1974

118

768

5296

Rot

-34

7044

199

210.

520.

0988

1.0

0.81

551.

40.

0599

1.0

0.70

606

1360

712

600

4410

1R

ot-3

514

7742

40.

470.

0948

0.9

0.77

482.

30.

0593

2.1

0.40

582

2058

410

578

9110

1R

ot-3

626

5668

80.

870.

1051

0.9

0.89

461.

40.

0617

1.1

0.65

649

1464

411

665

4697

Rot

-37

9091

272

260.

460.

0925

1.1

0.75

251.

40.

0590

0.9

0.76

570

1257

012

567

4110

1R

ot-3

848

5614

215

0.63

0.09

341.

00.

7783

1.5

0.06

041.

10.

6658

513

576

1161

947

93R

ot-3

929

6289

111.

140.

0965

0.9

0.79

821.

40.

0600

1.0

0.69

596

1259

411

603

4299

Rot

-40

1139

030

642

1.36

0.10

551.

30.

8858

1.6

0.06

090.

90.

8364

415

646

1663

638

102

Rot

-41

6613

8717

0.99

0.16

051.

01.

595

1.5

0.07

211.

20.

6596

819

959

1798

947

97R

ot-4

257

107

114

600.

390.

4688

1.0

12.1

711.

20.

1883

0.6

0.88

2618

2224

7843

2727

1891

Rot

-43

1189

535

539

0.86

0.09

650.

90.

7985

1.3

0.06

000.

90.

7359

611

594

1060

337

98R

ot-4

483

4335

140.

720.

3517

1.0

5.58

81.

40.

1153

1.0

0.72

1914

2419

4334

1884

3510

3R

ot-4

569

989

155

790.

340.

4540

1.0

10.9

701.

20.

1752

0.6

0.84

2521

2224

1340

2608

2193

Rot

-46

3745

118

130.

800.

0945

1.2

0.77

221.

60.

0592

1.1

0.75

581

1458

213

576

4610

1R

ot-4

737

5610

011

0.58

0.10

611.

10.

9046

1.5

0.06

191.

00.

7665

414

650

1466

941

97R

ot-4

835

8045

50.

840.

0974

0.9

0.80

431.

90.

0599

1.7

0.49

599

1859

911

600

7310

0R

ot-4

955

8117

018

0.69

0.09

461.

10.

7800

1.4

0.05

980.

90.

7858

513

583

1259

738

98R

ot-5

024

7145

50.

970.

0946

1.0

0.77

631.

70.

0595

1.3

0.60

583

1558

311

586

5899

Rot

-51

4638

155

160.

900.

0895

1.0

0.73

081.

30.

0592

0.9

0.74

557

1155

210

576

3896

Rot

-52

2468

404

0.47

0.10

281.

20.

8624

1.5

0.06

080.

90.

7763

114

631

1463

441

100

Rot

-53

8619

528

411

80.

060.

4132

1.0

7.71

71.

10.

1355

0.5

0.90

2199

1922

2936

2170

1610

3R

ot-5

489

8127

131

0.84

0.10

131.

10.

8433

1.4

0.06

040.

80.

8162

113

622

1361

635

101

Rot

-55

1676

960

240.

420.

3725

1.1

6.50

81.

40.

1267

0.9

0.75

2047

2520

4138

2053

3399

Rot

-56

1069

330

236

1.01

0.10

011.

00.

8384

1.4

0.06

070.

90.

7361

813

615

1263

040

98R

ot-5

749

118

159

690.

580.

3834

0.9

7.10

41.

00.

1344

0.5

0.88

2125

1820

9232

2156

1797

Rot

-58

1797

405

0.63

0.12

251.

01.

079

1.5

0.06

391.

00.

7274

315

745

1573

743

101

Rot

-59

1853

643

842

0.30

0.09

511.

20.

7890

1.4

0.06

020.

80.

8359

113

585

1361

134

96R

ot-6

0c21

0159

311

168

0.51

0.46

143.

09.

874

7.4

0.15

526.

70.

4124

2314

024

4612

424

0422

810

2R

ot-6

0r28

3975

488

193

0.26

0.34

491.

85.

897

2.4

0.12

401.

60.

7419

6142

1910

5920

1557

95

Not

e: C

oord

inat

es a

re U

TM

Wor

ld G

eode

tic S

yste

m 8

4. C

onc.

—co

ncor

danc

e.*W

ithin

-run

bac

kgro

und-

corr

ecte

d m

ean

207 P

b si

gnal

in c

ount

s pe

r se

cond

.† U

and

Pb

cont

ent a

nd T

h/U

rat

ios

wer

e ca

lcul

ated

rel

ativ

e to

GJ-

1 an

d ar

e ac

cura

te to

~10

%.

§ Cor

rect

ed fo

r ba

ckgr

ound

, mas

s bi

as, l

aser

indu

ced

U-P

b fr

actio

natio

n an

d co

mm

on P

b (if

det

ecta

ble,

see

text

on

anal

ytic

al m

etho

d) u

sing

the

Sta

cey

and

Kra

mer

s (1

975)

m

odel

Pb

com

posi

tion.

207

Pb/

235 U

cal

cula

ted

usin

g 20

7 Pb/

206 P

b/(23

8 U/20

6 Pb

× 1/

137.

88).

Err

ors

are

prop

agat

ed b

y qu

adra

tic a

dditi

on o

f with

in-r

un e

rror

s (1

sta

ndar

d er

ror)

and

the

repr

oduc

ibili

ty o

f GJ-

1 (1

sta

ndar

d de

viat

ion)

.**

Rho

is th

e er

ror

corr

elat

ion

defi n

ed a

s er

r206 P

b/23

8 U/e

rr20

7 Pb/

235 U

. See

text

for

deta

ils.

76 Linneman et al.

spe423-03 page 76

TAB

LE 2

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b, A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

PA

LAE

OZ

OIC

QU

AR

ZIT

ES

OF

TH

E E

LBE

ZO

NE

, S

AX

O-T

HU

RIN

GIA

N Z

ON

E, B

OH

EM

IAN

MA

SS

IF

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ (%)

Rho

**20

7 Pb

235 U

±2σ

(Ma)

206 P

b23

8 U±2

σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Kam

-1 (

Loca

tion:

san

dsto

ne, L

ower

Cam

bria

n, Z

wet

hau

For

mat

ion,

Tor

gau-

Dob

erlu

ng s

yncl

ine,

dril

l Wis

BaW

120

9/78

nea

r Fa

lken

berg

, dep

th o

f sam

ple

core

: 455

.5 m

,E

astin

g: 3

7 40

90, N

orth

ing:

57

1891

1)

Kam

-127

3340

61.

480.

1046

1.1

0.87

472.

20.

0606

1.9

0.49

638

2164

113

626

8210

2K

am-2

7205

022

286

0.26

0.36

371.

16.

4764

1.1

0.12

910.

40.

9220

4320

2000

3620

8616

96K

am-3

8653

201

301.

710.

1018

1.1

0.85

691.

40.

0610

1.0

0.74

628

1462

513

641

4298

Kam

-462

4911

816

0.78

0.11

311.

00.

9648

1.7

0.06

191.

40.

5968

617

691

1367

059

103

Kam

-576

6418

620

0.49

0.10

001.

20.

8387

1.6

0.06

091.

00.

7861

815

614

1463

442

97K

am-6

3002

080

074

0.22

0.09

431.

10.

7658

1.3

0.05

890.

70.

8557

712

581

1356

430

103

Kam

-754

0813

417

1.27

0.09

661.

10.

8008

1.5

0.06

011.

00.

7459

713

594

1260

843

98K

am-8

2415

455

0.44

0.10

441.

10.

8836

2.0

0.06

141.

70.

5464

319

640

1365

271

98K

am-9

4321

106

120.

510.

1017

1.1

0.84

761.

70.

0604

1.3

0.65

623

1662

513

619

5710

1K

am-1

038

8080

80.

490.

0982

1.1

0.82

721.

70.

0611

1.3

0.63

612

1660

412

641

5794

Kam

-11

2940

495

0.62

0.09

671.

20.

8097

1.8

0.06

071.

40.

6260

217

595

1363

062

94K

am-1

241

770

8749

0.97

0.44

151.

19.

868

1.2

0.16

210.

50.

9224

2322

2357

4424

7816

95K

am-1

376

368

340

116

0.62

0.30

201.

24.

639

1.3

0.11

140.

50.

9317

5622

1701

3618

2317

93K

am-1

480

1318

823

0.96

0.10

081.

10.

8391

1.5

0.06

041.

00.

7261

914

619

1361

845

100

Kam

-15

2506

3166

727

50.

380.

3749

1.2

7.07

41.

30.

1369

0.5

0.93

2121

2320

5243

2188

1794

Kam

-16

1450

040

538

0.41

0.08

851.

00.

7168

1.2

0.05

870.

60.

8554

910

547

1155

728

98K

am-1

728

4354

70.

910.

1095

1.2

0.92

212.

40.

0611

2.0

0.52

663

2367

016

643

8710

4K

am-1

889

961

850

142

0.04

0.17

421.

12.

255

1.5

0.09

391.

00.

7311

9821

1035

2015

0638

69K

am-1

980

1817

922

0.84

0.10

421.

10.

8847

1.6

0.06

161.

10.

7164

415

639

1465

948

97K

am-2

080

1817

922

0.84

0.10

421.

10.

8865

1.5

0.06

171.

00.

7464

414

639

1466

543

96K

am-2

174

0019

320

0.72

0.09

281.

10.

7667

1.4

0.05

991.

00.

7357

813

572

1260

143

95K

am-2

233

4282

90.

750.

0983

1.2

0.80

521.

80.

0594

1.4

0.63

600

1760

513

582

6110

4K

am-2

335

884

109

541.

240.

3742

1.1

6.65

41.

20.

1290

0.6

0.87

2067

2220

4937

2084

2198

Kam

-24

5711

132

160.

680.

1080

1.3

0.91

321.

80.

0613

1.2

0.74

659

1766

116

651

5110

2K

am-2

536

8086

90.

480.

0959

1.1

0.79

571.

50.

0602

1.1

0.72

594

1459

112

609

4697

Kam

-26

7305

174

210.

860.

1011

1.2

0.84

371.

50.

0605

0.9

0.82

621

1462

114

622

3710

0K

am-2

797

5519

926

1.99

0.10

181.

20.

8564

1.7

0.06

101.

20.

7062

816

625

1463

952

98K

am-2

889

9523

725

0.62

0.09

451.

20.

7728

1.5

0.05

930.

90.

7958

113

582

1357

840

101

Kam

-29

6203

814

066

0.60

0.40

521.

07.

639

1.5

0.13

671.

10.

6821

9027

2193

3721

8638

100

Kam

-30

4117

9412

0.98

0.10

181.

20.

8521

1.8

0.06

071.

30.

6962

617

625

1562

955

99K

am-3

179

5417

324

1.38

0.10

410.

80.

8845

1.2

0.06

160.

90.

6564

311

638

966

139

97K

am-3

239

8855

70.

800.

1098

0.7

0.94

651.

40.

0625

1.2

0.52

676

1467

110

692

5397

Kam

-33

5413

132

171.

100.

1030

0.8

0.85

471.

80.

0602

1.6

0.44

627

1763

29

610

6910

4K

am-3

442

0211

211

0.31

0.09

560.

90.

7930

1.8

0.06

021.

60.

4959

316

589

1060

968

97K

am-3

544

1212

312

0.58

0.09

180.

80.

7536

1.4

0.05

951.

10.

6057

012

566

958

647

97K

am-3

610

866

311

290.

280.

0928

0.8

0.75

121.

10.

0587

0.8

0.67

569

1057

28

556

3610

3K

am-3

753

8611

814

0.56

0.10

910.

80.

9149

1.5

0.06

081.

20.

5766

014

667

1163

451

105

Kam

-38

3379

8513

1.71

0.09

990.

80.

8255

1.7

0.05

991.

50.

4961

116

614

1060

064

102

Kam

-39

3660

104

100.

460.

0866

0.9

0.70

601.

50.

0591

1.2

0.59

542

1353

59

572

5294

Kam

-40

3327

445

0.88

0.09

241.

20.

7713

3.0

0.06

062.

80.

3958

127

570

1362

312

091

Kam

-41

4189

100

120.

630.

1070

0.8

0.90

181.

30.

0611

1.1

0.60

653

1365

510

644

4610

2K

am-4

239

1460

70.

680.

0971

0.8

0.80

661.

80.

0602

1.6

0.46

601

1659

79

612

6898

Con

tinue

d


spe423-03 page 77

TAB

LE 2

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b, A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

PA

LAE

OZ

OIC

QU

AR

ZIT

ES

OF

TH

E E

LBE

ZO

NE

, S

AX

O-T

HU

RIN

GIA

N Z

ON

E, B

OH

EM

IAN

MA

SS

IF (

cont

inue

d)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ (%)

Rho

**20

7 Pb

235 U

±2σ

(Ma)

206 P

b23

8 U±2

σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Kam

-1 (

cont

inue

d)

Kam

-43

4659

129

140.

770.

0966

0.8

0.79

791.

40.

0599

1.1

0.60

596

1359

410

601

4999

Kam

-44

9519

3215

1.04

0.36

750.

86.

424

1.3

0.12

681.

00.

6320

3624

2018

2920

5437

98K

am-4

520

7350

60.

980.

0951

0.9

0.78

661.

60.

0600

1.3

0.55

589

1458

610

603

5897

Kam

-46

7097

141

140.

630.

0889

1.0

0.71

581.

60.

0584

1.3

0.59

548

1454

910

545

5710

1K

am-4

736

3016

20.

860.

1051

1.0

0.87

132.

80.

0601

2.6

0.34

636

2764

412

608

114

106

Kam

-48

3850

9112

1.38

0.09

920.

80.

8177

1.8

0.05

981.

70.

4460

717

610

959

772

102

Kam

-50

3271

374

0.39

0.09

890.

90.

8306

1.9

0.06

091.

70.

4761

418

608

1063

672

96K

am-5

126

7366

91.

590.

1080

0.8

0.91

961.

60.

0618

1.4

0.46

662

1666

19

666

6299

Kam

-52

1515

317

230

0.35

0.16

940.

91.

727

1.1

0.07

390.

70.

7910

1915

1009

1710

4028

97K

am-5

383

6119

624

0.99

0.10

360.

90.

8820

1.2

0.06

170.

80.

7364

211

636

1066

435

96K

am-5

418

610

352

441.

180.

0978

0.8

0.81

091.

00.

0602

0.7

0.75

603

1060

19

609

3099

Kam

-55

3730

013

352

0.38

0.36

151.

26.

208

1.3

0.12

450.

60.

8820

0623

1989

4020

2223

98K

am-5

671

5417

219

0.59

0.09

970.

90.

8244

1.6

0.06

001.

40.

5461

015

613

1060

259

102

Kam

-57

7995

207

230.

520.

1015

0.9

0.85

251.

30.

0609

1.0

0.68

626

1262

311

636

4298

Kam

-58

3800

818

0.56

0.09

060.

80.

7467

2.5

0.05

982.

40.

3156

622

559

859

510

594

Kam

-59

6430

3915

0.30

0.36

270.

86.

457

1.3

0.12

911.

00.

6320

4023

1995

2820

8635

96K

am-6

027

906

756

770.

580.

0950

0.9

0.78

571.

00.

0600

0.6

0.82

589

958

510

602

2697

Lang

erbe

rg Q

uart

zite

(Lo

catio

n: m

icro

cong

lom

erat

e, L

ower

Ord

ovic

ian,

Tre

mad

oc, L

ange

r B

erg

For

mat

ion,

Sch

war

zbur

g an

tifor

m [n

orth

wes

tern

par

t], L

ange

r B

erg

near

W

illm

ersd

orf,

Eas

ting:

64

3489

, Nor

thin

g: 5

6 09

502)

Lbq_

110

3842

247

950.

030.

3873

1.3

7.46

71.

80.

1398

1.2

0.74

2169

3221

1048

2225

4195

Lbq_

211

930

148

150.

510.

1058

1.0

0.88

334.

10.

0605

4.0

0.25

643

4064

812

623

172

104

Lbq_

310

574

239

220.

620.

0958

1.0

0.77

451.

30.

0587

0.8

0.78

582

1159

011

554

3510

6Lb

q_4

2675

810

734

0.57

0.29

791.

24.

528

1.4

0.11

020.

70.

8517

3623

1681

3418

0326

93Lb

q_5

5224

316

863

0.42

0.34

761.

05.

628

1.1

0.11

740.

50.

9119

2020

1923

3519

1717

100

Lbq_

615

342

360

320.

490.

0910

1.0

0.73

691.

10.

0587

0.6

0.85

561

1056

211

557

2610

1Lb

q_7

2171

1215

714

91.

080.

7058

1.2

28.3

71.

30.

2915

0.6

0.89

3432

2634

4362

3426

1910

1Lb

q_8

5306

110

110.

450.

1011

1.0

0.84

191.

90.

0604

1.6

0.53

620

1862

112

617

6910

1Lb

q_9

2472

970

280.

800.

3720

1.1

6.27

51.

20.

1223

0.6

0.87

2015

2220

3937

1991

2210

2Lb

q_10

1401

433

128

0.14

0.08

611.

30.

6943

1.5

0.05

850.

90.

8353

513

532

1354

838

97Lb

q_11

1786

240

440

0.42

0.09

271.

20.

7409

1.4

0.05

800.

70.

8856

312

571

1352

929

108

Lbq_

1226

4462

60.

420.

0930

1.1

0.75

421.

80.

0588

1.5

0.58

571

1657

312

561

6510

2Lb

q_13

3910

778

0.45

0.09

221.

00.

7727

3.5

0.06

083.

40.

2958

131

568

1163

214

590

Lbq_

1434

784

864

700.

310.

0795

1.2

0.63

871.

30.

0583

0.7

0.87

502

1149

311

539

2991

Lbq_

1510

562

239

240.

250.

1003

1.1

0.82

281.

50.

0595

1.0

0.74

610

1461

613

585

4310

5Lb

q_16

1115

324

725

0.43

0.09

581.

00.

7707

1.3

0.05

840.

80.

7858

012

590

1254

436

108

Lbq_

1758

3011

111

0.32

0.10

451.

10.

9071

1.9

0.06

301.

60.

5665

518

640

1370

766

91Lb

q_18

1375

130

030

0.66

0.10

301.

00.

8443

1.3

0.05

940.

80.

8062

212

632

1358

434

108

Lbq_

1911

9431

353

128

0.15

0.35

881.

25.

811

1.3

0.11

750.

70.

8719

4823

1977

3919

1824

103

Lbq_

2030

878

7635

0.74

0.37

951.

06.

896

1.1

0.13

180.

50.

9020

9820

2074

3521

2217

98Lb

q_21

5795

375

430.

390.

4966

1.0

13.6

51.

10.

1994

0.5

0.87

2726

2125

9942

2821

1892

Lbq_

2255

794

145

620.

550.

3761

1.0

6.53

61.

10.

1260

0.5

0.90

2051

2020

5836

2043

1810

1

Con

tinue

d

78 Linneman et al.

spe423-03 page 78

TAB

LE 2

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

b, A

ND

Th

DAT

A O

F D

ET

RIT

AL

ZIR

CO

N G

RA

INS

FR

OM

PA

LAE

OZ

OIC

QU

AR

ZIT

ES

OF

TH

E E

LBE

ZO

NE

, S

AX

O-T

HU

RIN

GIA

N Z

ON

E, B

OH

EM

IAN

MA

SS

IF (

cont

inue

d)

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ (%)

Rho

**20

7 Pb

235 U

±2σ

(Ma)

206 P

b23

8 U±2

σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Lang

erbe

rg Q

uart

zite

(co

ntin

ued)

Lbq_

2314

6269

329

148

0.44

0.40

811.

07.

611

1.1

0.13

520.

40.

9221

8619

2206

3721

6715

102

Lbq_

2412

6831

30.

590.

0915

1.0

0.73

882.

40.

0585

2.2

0.40

562

2156

510

550

9710

3Lb

q_25

6566

118

120.

660.

1024

1.0

0.86

391.

40.

0612

1.0

0.72

632

1462

812

647

4397

Lbq_

2614

8581

182

109

0.28

0.53

861.

014

.06

1.1

0.18

940.

40.

9427

5420

2777

4627

3712

101

Lbq_

2712

729

265

290.

420.

1021

1.0

0.83

191.

50.

0591

1.1

0.68

615

1462

712

571

4911

0Lb

q_28

1295

7325

911

70.

340.

4159

1.0

7.94

21.

20.

1385

0.6

0.87

2224

2222

4239

2208

2010

2Lb

q_29

6445

891

470.

080.

4964

1.1

12.9

21.

30.

1888

0.7

0.86

2674

2525

9848

2732

2295

Lbq_

3040

378

964

960.

610.

0882

1.1

0.72

441.

30.

0595

0.7

0.86

553

1154

512

587

2893

Lbq_

3155

1562

90.

320.

1461

1.5

1.40

92.

00.

0700

1.4

0.73

893

2487

924

927

5795

Lbq_

3293

4018

422

0.89

0.09

890.

80.

8140

1.1

0.05

970.

80.

7560

510

608

1059

433

102

Lbq_

3315

446

339

330.

460.

0916

0.9

0.75

231.

20.

0596

0.9

0.70

570

1156

59

588

3796

Lbq_

3414

116

262

270.

520.

0946

0.8

0.77

611.

20.

0595

0.8

0.70

583

1158

39

585

3710

0Lb

q_35

6388

861

765

0.32

0.08

531.

00.

6956

2.1

0.05

911.

80.

4853

617

528

1057

279

92Lb

q_36

3083

297

390.

640.

3407

0.9

5.74

91.

10.

1224

0.6

0.83

1939

1918

9030

1991

2295

Lbq_

3722

6574

167

127

0.40

0.63

660.

822

.40

0.9

0.25

520.

50.

8732

0118

3175

4032

1714

99Lb

q_38

2440

857

058

0.72

0.08

860.

90.

7189

1.1

0.05

880.

70.

7955

010

547

956

131

98Lb

q_39

1078

012

014

0.28

0.09

980.

80.

8294

1.0

0.06

020.

70.

7661

39

614

961

229

100

Lbq_

4027

007

529

580.

540.

1012

0.8

0.85

780.

90.

0615

0.5

0.83

629

962

19

657

2395

Lbq_

4180

5019

419

0.61

0.08

840.

70.

7173

1.1

0.05

890.

80.

6354

99

546

756

237

97Lb

q_42

2250

127

228

0.47

0.09

550.

70.

7759

2.1

0.05

892.

00.

3358

319

588

856

486

104

Lbq_

4384

932

236

920.

500.

3473

0.6

7.18

70.

70.

1225

0.4

0.87

1956

1319

2121

1993

1396

Lbq_

4482

4526

110.

330.

3971

0.9

0.65

61.

40.

1313

1.1

0.65

2135

2521

5634

2115

3810

2Lb

q_45

2060

713

612

0.43

0.08

120.

90.

6557

2.0

0.05

861.

80.

4551

216

503

955

077

91Lb

q_46

3704

8948

822

70.

020.

4461

1.0

12.0

11.

10.

1952

0.4

0.95

2605

2023

7841

2787

1285

Lbq_

4713

1963

173

118

1.14

0.51

170.

813

.09

0.8

0.18

550.

30.

9226

8616

2664

3327

0311

99Lb

q_48

2950

272

300.

460.

3665

0.7

6.93

00.

90.

1371

0.6

0.79

2103

1720

1326

2191

2092

Lbq_

4931

150

701

640.

480.

0880

1.2

0.71

371.

70.

0588

1.2

0.73

547

1454

413

561

5197

Lbq_

5069

1114

215

0.59

0.09

640.

70.

8044

1.2

0.06

051.

00.

5859

911

593

862

343

95Lb

q_51

1637

835

937

0.62

0.09

300.

90.

7566

1.2

0.05

900.

90.

7157

211

574

1056

638

101

Lbq_

5339

7784

100.

790.

0965

0.7

0.80

321.

30.

0604

1.1

0.55

599

1259

48

616

4896

Lbq_

5410

025

181

180.

660.

0880

1.2

0.70

371.

80.

0580

1.3

0.68

541

1554

413

529

5810

3Lb

q_55

1569

633

032

0.40

0.09

170.

80.

7641

1.2

0.06

050.

80.

7157

611

565

962

037

91Lb

q_56

2526

757

752

0.28

0.08

870.

80.

7167

1.0

0.05

860.

60.

7954

98

548

855

327

99Lb

q_57

2590

6241

921

50.

510.

4447

1.0

10.1

41.

10.

1654

0.6

0.85

2448

2123

7138

2511

2094

Lbq_

5813

896

152

290.

820.

1607

0.9

1.57

71.

20.

0712

0.9

0.68

961

1696

115

963

3710

0Lb

q_59

7482

156

201.

180.

1001

0.7

0.83

451.

30.

0605

1.1

0.56

616

1261

59

620

4799

Lbq_

6030

8864

70.

830.

0873

0.8

0.70

411.

80.

0585

1.6

0.42

541

1554

08

547

7199

Not

e: C

oord

inat

es a

re U

TM

Wor

ld G

eode

tic S

yste

m 8

4. C

onc.

—co

ncor

danc

e.*W

ithin

-run

bac

kgro

und-

corr

ecte

d m

ean

207 P

b si

gnal

in c

ount

s pe

r se

cond

.† U

and

Pb

cont

ent a

nd T

h/U

rat

io w

ere

calc

ulat

ed r

elat

ive

to G

J-1

and

are

accu

rate

to ~

10%

.§ C

orre

cted

for

back

grou

nd, m

ass

bias

, las

er in

duce

d U

-Pb

frac

tiona

tion

and

com

mon

Pb

(if d

etec

tabl

e; s

ee te

xt o

n an

alyt

ical

met

hod)

usi

ng th

e S

tace

y an

d K

ram

ers

(197

5)

mod

el P

b co

mpo

sitio

n. 2

07P

b/23

5 U c

alcu

late

d us

ing

207 P

b/20

6 Pb/

(238 U

/206 P

b ×

1/13

7.88

). E

rror

s ar

e pr

opag

ated

by

quad

ratic

add

ition

of w

ithin

-run

err

ors

(1 s

tand

ard

erro

r) a

nd

the

repr

oduc

ibili

ty o

f GJ-

1 (1

sta

ndar

d de

viat

ion)

.**

Rho

is th

e er

ror

corr

elat

ion

defi n

ed a

s er

r206 P

b/23

8 U/e

rr20

7 Pb/

235 U

. See

text

for

deta

ils.


spe423-03 page 79

TAB

LE 3

. LA

SE

R A

BLA

TIO

N-I

CP

-MS

U, P

B, A

ND

TH

DAT

A O

F Z

IRC

ON

FR

OM

PY

RO

CLA

ST

IC S

ED

IME

NT

S O

F T

HE

SA

XO

-TH

UR

ING

IAN

ZO

NE

, BO

HE

MIA

N M

AS

SIF

Isot

opic

rat

ios§

Age

s

Sam

ple

207 P

b*(c

ps)

U†

(ppm

)P

b†

(ppm

)T

h†

U

206 P

b23

8 U1σ (%

)

207 P

b23

5 U1σ (%

)

207 P

b20

6 Pb

1σ (%)

Rho

**20

7 Pb

235 U

±2σ

(Ma)

206 P

b23

8 U±2

σ(M

a)

207 P

b20

6 Pb

±2σ

(Ma)

Con

c(%

)

Ves

1 (L

ocat

ion:

rhy

oliti

c ig

nim

brite

, Upp

er C

ambr

ian,

Rol

lkop

f For

mat

ion,

Ves

ser

com

plex

, old

qua

rry

clos

e to

the

ski-j

ump

at S

chm

iede

feld

, Eas

ting:

62

8631

, Nor

thin

g: 5

6 06

911)

Ves

1_1

1117

429

124

0.41

0.07

980.

60.

6268

1.2

0.05

701.

10.

5149

410

495

649

147

101

Ves

1_2

1502

340

736

0.71

0.07

980.

50.

6335

1.0

0.05

760.

90.

5449

88

495

551

537

96V

es1_

318

762

505

450.

710.

0800

0.7

0.63

461.

10.

0576

0.8

0.63

499

849

67

513

3797

Ves

1_4

1511

031

730

0.76

0.08

160.

80.

6496

1.2

0.05

770.

90.

6850

89

506

852

037

97V

es1_

566

1217

815

0.55

0.07

980.

80.

6255

1.2

0.05

691.

00.

6349

310

495

848

742

102

Ves

1_6

1132

127

025

0.79

0.08

020.

60.

6254

1.1

0.05

660.

90.

5949

38

497

647

539

105

Ves

1_7

3239

087

084

0.53

0.08

130.

70.

6436

1.1

0.05

740.

80.

6650

59

504

750

636

100

Ves

1_8

2147

560

257

0.96

0.08

020.

50.

6340

1.2

0.05

741.

10.

4549

99

497

550

547

98V

es1_

910

974

262

230.

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0804

0.8

0.63

401.

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499

1149

98

499

5110

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es1_

1065

1218

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80.

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1.2

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670.

90.

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500

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1751

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80.

6293

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0.05

690.

90.

6349

69

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748

841

102

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1_12

1731

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940

0.59

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80.

6404

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0.05

760.

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7350

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500

851

435

97V

es1_

1344

335

1259

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0.27

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80.

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721.

00.

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110

489

850

043

98V

es1_

1464

1017

415

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0.08

060.

90.

6385

1.3

0.05

750.

90.

7150

110

500

951

040

98V

es1_

1524

741

665

620.

820.

0800

0.9

0.63

591.

30.

0577

0.9

0.73

500

1049

69

518

3996

kArc

1 (L

ocat

ion:

peb

ble-

bear

ing

rhyo

lithi

c tu

ffi te

(tr

aditi

onal

term

in th

e ol

der

Ger

man

ref

eren

ces:

“K

ongl

omer

atis

che

Ark

ose”

), L

ower

Ord

ovic

ian,

Tre

mad

ocia

n, G

oldi

stha

l For

mat

ion,

S

chw

arzb

urg

antif

orm

[sou

thea

ster

n pa

rt],

valle

y of

the

Bla

mba

ch n

ear

Sitz

endo

rf, E

astin

g: 6

5 24

47, N

orth

ing:

56

1173

2)

kArc

-16

5093

127

110.

640.

0773

1.8

0.60

292.

40.

0566

1.6

0.74

479

1848

016

475

7010

1kA

rc-1

753

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511

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0.07

901.

40.

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2.3

0.05

731.

90.

6149

318

490

1450

382

98kA

rc-1

860

4212

612

0.68

0.07

951.

50.

6197

1.8

0.05

661.

00.

8349

014

493

1447

444

104

kArc

-19

5438

152

130.

760.

0746

1.7

0.58

452.

10.

0569

1.3

0.80

467

1646

415

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5695

kArc

-20

6145

265

210.

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0784

1.6

0.61

801.

90.

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1.1

0.81

489

1548

615

499

5098

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879

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30.

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1849

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210

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721.

90.

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1.4

0.67

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1547

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rc-3

244

2711

910

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0.07

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50.

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0.05

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90.

8449

214

491

1449

841

99kA

rc-3

311

356

318

230.

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012

429

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3

Not

e: C

oord

inat

es a

re U

TM

Wor

ld G

eode

tic S

yste

m 8

4. C

onc.

—co

ncor

danc

e.*W

ithin

-run

bac

kgro

und-

corr

ecte

d m

ean

207 P

b si

gnal

in c

ount

s pe

r se

cond

.† U

and

Pb

cont

ent a

nd T

h/U

rat

io w

ere

calc

ulat

ed r

elat

ive

to G

J-1

and

are

accu

rate

to ~

10%

.§ C

orre

cted

for

back

grou

nd, m

ass

bias

, las

er in

duce

d U

-Pb

frac

tiona

tion

and

com

mon

Pb

(if d

etec

tabl

e; s

ee te

xt o

n an

alyt

ical

met

hod)

usi

ng th

e S

tace

y an

d K

ram

ers

(197

5) m

odel

Pb

com

posi

tion.

207

Pb/

235 U

cal

cula

ted

usin

g 20

7 Pb/

206 P

b/(23

8 U/20

6 Pb

× 1/

137.

88).

Err

ors

are

prop

agat

ed b

y qu

adra

tic a

dditi

on o

f with

in-r

un e

rror

s (1

sta

ndar

d er

ror)

and

the

repr

oduc

ibili

ty o

f G

J-1

(1 s

tand

ard

devi

atio

n).

**R

ho is

the

erro

r co

rrel

atio

n de

fi ned

as

err20

6 Pb/

238 U

/err

207 P

b/23

5 U. S

ee te

xt fo

r de

tails

.

80 Linneman et al.

spe423-03 page 80

was used to enable sequential sampling of heterogeneous grains (e.g., growth zones) during time-resolved data acquisition (see also Janoušek et al., 2006). Each analysis consisted of ~20 s back-ground acquisition followed by 35 s data acquisition, using a laser spot size of 30 and 40 μm, respectively. A common-Pb correction based on the interference- and background-corrected 204Pb signal and a model Pb composition (Stacey and Kramers, 1975) was car-ried out if necessary. The necessity of the correction is based on whether the corrected 207Pb/206Pb lies outside of the internal errors of the measured ratios. Discordant analyses were generally inter-preted with care. Raw data were corrected for background signal, common Pb, laser-induced elemental fractionation, instrumental mass discrimination, and time-dependant elemental fraction-ation of Pb/Th and Pb/U using an Excel® spreadsheet program. Reported uncertainties were propagated by quadratic addition of the external reproducibility (standard deviation) obtained from the standard zircon GJ-1 (n = 18; ~0.6% and 0.5–1.0% for the 207Pb/206Pb and 206Pb/238U, respectively) during individual analyti-cal sessions and the within-run precision of each analyses (stan-dard error). Concordia diagrams (2σ error ellipses) and concordia ages (95% confi dence level) were produced using Isoplot/Ex 2.49 (Ludwig, 2001) and frequency and relative probability plots using AgeDisplay (Sircombe 2004). The 207Pb/206Pb age was taken for interpretation for all zircons >1.0 Ga, and the 206Pb/238U ages was used for younger grains. For further details on analytical protocol and data processing see Gerdes and Zeh (2006).

RESULTS

The results of LA-ICP-MS U-Pb zircon dating are listed in Tables 1–3 and shown on the concordia diagrams in Figures 7, 9, and 11 (see below). Binned frequency and probability density distribution plots are shown in Figures 8 and 10. For the latter two plots only those analyses less than 10% discordant were used. In this study, all systems, erathems, and eonothems are used in accordance with the stratigraphic table of Gradstein et al., (2004). Percentages of zircon ages for each sample are shown in Table 4. For zircons older than 1.0 Ga, the 207Pb/206Pb age is mentioned in the text. Younger zircon ages refer to the 206Pb/238U age.

From sample Pur-1, seventy-four detrital zircon grains were analyzed, sixty-seven of which yielded concordant ages (Figs. 7 and 8). The age of the youngest concordant grain is 558 ± 16 Ma, and that of the oldest is 3465 ± 20 Ma (Table 1). Archean ages make up ~21% of the population. These ages fall into two groups at 3.5–3.3 Ga (six grains) and at 2.9–2.6 Ga (nine grains). About 33% of the grains record Paleoproterozoic ages between 1.8 and 2.3 Ga and nearly 45% record Neoproterozoic ages. The later group show pronounced peaks at ca. 640, ca. 620–590, and ca. 570 Ma and less pronounced peaks at ca. 710, ca. 790, and ca. 1000–950 Ma (Fig. 8, Table 4).

All sixty-one analyses from sample Roth-1 are 90–110% concordant (Figs. 7 and 8). The ages range from 552 ± 11 Ma to 3053 ± 11 Ma. Only 5% of the analyzed grains are Archean in age, ~20% Paleoproterozoic, and ~75% Neoproterozoic.

3200

2800

2400

2000

1600

0.2

0.4

0.6

0 4 8 12 16 20 24 28

1200

206Pb238U

Wett-1 n = 61

900

800

700

600

0.12

0.14

0.16

1.0

1.2

1.4

1.6

207Pb/235U

3000

2600

2200

1800

1400

10000.2

0.4

0.6

0 4 8 12 16 20

Roth-1 n = 61

900

800

700

600

0.12

0.14

0.16

1.0

1.2

1.4

1.6

206Pb238U

0.2

0.4

0.6

3200

2800

2400

2000

1600

0 4 8 12 16 20 24 28

206Pb238U

Pur-1 n = 74

1200

900

800

700

600

0.12

0.14

0.16

1.0

1.2

1.4

1.6

data-point error ellipses are 2σ

Figure 7. Concordia plots of LA-ICP-MS U-Pb analyses of detrital zir-con grains from Late Neoproterozoic (Ediacaran) sedimentary rocks of the Saxo-Thuringian zone: Purpurberg quartzite from the Weesenstein Group (Pur-1), microconglomerate from the Lausitz Group (Wett-1), and graywacke from the Rothstein Formation (Roth-1). Error ellipses are 2σ. Insets show enlargement of the younger ages. n—number of analyses. For sample details see Table 1.


spe423-03 page 81

0

2

4

6

8

10

12

14

500

600

700

800

900

100 0

110 0

1600

18 00

200 0

220 0

2400

26 00

280 0

3000

320 0

34 00F

req

uen

cy

Roth-1 (Neoproterozoic)

n=61/61, 90-110% conc.

n=46/4690–110% conc.

Rla

ie

Pr

abli

ye

tv

ob

it n=15/15

90–110% conc.

Pur-1 (Neoproterozoic)

n=67/74, 90-110% conc.

0

1

2

3

4

5

6

7

8

9

105006007008009 00100 01100120 01 3001 400150 01 600170 018001 9002000210 0220023002 400250 02 6002700280 02 900300 03 100320 03 300340 0

Age (Ma)

Fre

qu

ency

n=31/3290–110% conc.

n=36/4290–110% conc.

500

600

700

80 0

900

100 0

11 00

1600

180 0

200 0

220 0

2400

2600

28 00

300 0

320 0

3400

Ra

ie

ra

iy

elt

vP

ob

bil

tt

vb

it

Rel

ai

eP

roab

liy

Wett-1 (Neoproterozoic)

n=59/61, 90-110% conc.

0

2

4

6

8

10

12

14

16

Fre

qu

ency

n=39/3990–110% conc.

500

600

700

800

90 0

10 00

1 100

160 0

18 00

20 00

22 00

2 400

2 600

2 800

30 00

32 00

3 400

N=20/2290–110% conc.

Figure 8. Binned frequency and probability density distribution plots of detrital zircon grains from Late Neoproterozoic (Ediacaran) sandstones of the Saxo-Thuringian zone. conc.—concordance; n—number of analyses with <10% discordance/total number of analyzed grains.

82 Linneman et al.

spe423-03 page 82

Archean ages (three grains) range from 3.05 to 2.6 Ga, Paleopro-terozoic ages from 2.17 to 1.78 Ga, and the Neoproterozoic ages fall mainly in the interval 650–550 Ma. There are clear clusters at ca. 612 (nine grains) and ca. 642 Ma (six grains), whereas the age range 600–550 Ma is defi ned by a broad peak (Fig. 8). In addi-tion, minor peaks occur at 710, ca. 740, ca. 790, and ca. 960 Ma, similar to those of Pur-1.

From sample Wett-1, sixty-one zircon grains were ana-lyzed, of which fi fty-nine are 90–110% concordant (Figs. 7 and 8). The ages vary from 3181 to 542 ± 27 Ma, of which ~10% are Archean, 24% Paleoproterozoic, and ~60% Neoproterozoic. Archean ages range from 3.2 to 2.6 Ga with a cluster at ca. 2.8–2.6 Ga (fi ve grains). Paleoproterozoic ages (fi fteen grains) defi ne several peaks in the range 2.17–1.76 Ga, whereas Neoprotero-zoic ages fall mostly in the interval 650 –540 Ma, with fi ve rela-tively well-defi ned clusters at ca. 642 (six grains), 625–610 (fi ve grains), ca. 590 (ten grains), ca. 572 (fi ve grains), and ca. 543 Ma (fi ve grains). The latter subpopulation yields a concordia age of 543 ± 4 Ma (see Fig. 11A), which straddles the Precambrian- Cambrian boundary (542 ± 1 Ma; Bowring et al., 2003).

From the Cambrian sandstone Kam-1 we analyzed fi fty-nine zircons, only one of which is more than 10% discordant (Figs. 9 and 10). No Archean and only nine Paleoproterozoic grains (15%) were identifi ed, although the age of the oldest grain (2478 ± 16 Ma), which is close to the Archean boundary, must be con-sidered a minimum age. Paleoproterozoic ages fall mostly in the interval 2.1–2.0 Ga, with one grain yielding a 206Pb/238U age of 1000 ± 18 Ma. Neoproterozoic ages, which make up more than 80% of the population, fall predominantly in the interval 690–550 Ma. The latter population shows clear clusters at ca. 570, ca. 590, ca. 610, ca. 623, ca. 643, and ca. 665 Ma, each of which is represented by six to nine grains. Two grains yielded ages of ca. 547 Ma, and one grain yielded a 206Pb/238U age of ca. 535 ± 9 Ma. The latter analysis is ~6% discordant but is considered to provide a maximum depositional age constraint.

From the Lower Ordovician microconglomerate Lbq-1 we analyzed fi fty-nine zircons; fi fty-seven analyses yielded 90–110% concordant ages, of which 12% are Archean (seven grains), 23% Paleoproterozoic (thirteen grains) and 60% Neo-proterozoic to Cambrian. The Archean grains yielded ages of ca. 2511, ca. 2820–2700 (four grains), ca. 3217, and ca. 3246 Ma. The Paleoproterozoic ages defi ne six peaks in the interval 2200–1800 Ma (Fig. 10) and Neoproterozoic ages (thirty-three grains) fall predominantly in the interval 650–540 Ma, with a broader peak at ca. 636 Ma and clear clusters at ca. 615, ca. 590, ca. 570, and ca. 546 Ma, each defi ned by fi ve to seven analyzed grains. The latter subpopulation of seven grains yielded a concordia age of 546 ± 4 Ma, which straddles the Precambrian-Cambrian boundary like that of Wett-2. In addition, two grains yielded ages close to the Neo-Mesoproterozoic boundary (927 ± 57 and 961 ± 16 Ma), and two others gave a Cambrian concordia age of 530 ± 8 Ma. The two youngest grains (503 ± 8 and 493 ± 12 Ma) straddle the Cambrian-Ordovician boundary close to the deposi-tion age of the sample. The Th/U ratio of most of the measured

TAB

LE 4

. PO

PU

LAT

ION

S A

ND

PE

RC

EN

TAG

ES

OF

ALL

ZIR

CO

NS

CO

NC

OR

DA

NT

BE

TW

EE

N 9

0% A

ND

110

%

Sam

ple

Sed

imen

t. ag

eTo

tal

num

ber

of

grai

ns

Sam

ple

Neo

prot

eroz

oic-

Cam

bria

n tr

ansi

tion

inte

rval

Late

N

eopr

oter

ozoi

cM

id-

Neo

prot

eroz

oic

Neo

-M

esop

rote

rozo

ic

tran

sitio

n in

terv

al

Pal

eopr

oter

ozoi

cN

eo-

to

Mes

oarc

hean

Pal

eoar

chea

n

Rift

ing

Cad

omia

n re

troa

rcC

adom

ian

back

-arc

Rod

inia

br

eak-

upG

renv

illia

nE

burn

ean

Libe

rian

Leon

ian

(ca.

490

–53

5 M

a)(c

a. 5

40–

545

Ma)

(ca.

550

–69

0 M

a)(c

a. 7

00–

790

Ma)

(ca.

900

–10

50 M

a)(c

a. 1

7,05

0–24

80 M

a)(c

a. 2

510–

3180

Ma)

(ca.

322

0–34

65 M

a)

Pur

-1N

eopr

oter

ozoi

c67

00

40 %

3 %

3 %

33 %

13 %

8 %

Rot

h-1

Neo

prot

erzo

ic61

00

66 %

8 %

1 %

20 %

5 %

0W

ett-

1N

eopr

oter

ozoi

c.59

08

%48

%3

%7

%24

%10

%0

Kam

-1Lo

wer

Cam

bria

n58

00

83 %

02

%15

%0

0Lb

q-1

Low

er O

rddo

vici

an57

9 %

5 %

47 %

04

%23

%9

%3

%

Not

e: T

he to

tal r

ange

of m

easu

red

U/P

b ag

es o

f eac

h po

pula

tion

are

show

n in

par

enth

eses

.


spe423-03 page 83

207Pb/235U

3200

2800

2400

2000

1600

0 4 8 12 16 20 24 28

206Pb238U

Lbq-1 n = 59

900

800

700

600

0.12

0.14

0.16

1.0

1.2

1.4

1.6

0.2

0.4

0.6

data-point error ellipses are 2σ

0.2

0.4

0.63200

2800

2400

2000

1600

0 4 8 12 16 20 24 28

Kam-1 n = 59206Pb238U

1000

800

700

600

0.12

0.14

0.16

1.0

1.2

1.4

1.6

900

207Pb/235UFigure 9. Concordia plots of LA-ICP-MS U-Pb analyses of detrital zircon grains from Lower Cambrian sandstone (Kam-1) and Early Ordovi-cian microconglomerate (Lbq-1) of the Saxo-Thuringian zone. Error ellipses are 2σ. Insets show enlargement of the younger ages. n—number of analyses. For sample details see Table 2.

n=58/59, 90-110% conc.

0

2

4

6

8

10

12

14

4005006007 008009 001000110012001 30 01 4001 5001 6001 70 01 80019002 0002 10 022002 30 02 40 02 500260 02 70 02 8002 9003 000310032003 30034 00

Age (Ma)

Fre

qu

ency

Kam-1 (Lower Cambrian)

n=49/4990–110% conc.

ate

oR

eliv

Pr

bab

ility

500

4 00

60 0

700

80 0

9 00

10 0 0

1 10 0

1600

1 800

2 000

2 20 0

2400

26 00

2800

3 0 00

3200

3 400

n=9/990–110% conc.

0

1

2

3

4

5

6

7

8

9

Fre

qu

ency

Lbq-1 (Lower Ordovician)n=57/59, 90-110% conc.

n=20/2190–110% conc.

n=37/3890–110% conc.

Rel

ativ

eP

rob

abili

ty

500

4 00

6 00

700

800

900

100 0

110 0

16 00

180 0

2000

2200

2400

2600

28 00

3000

3200

3400

Figure 10. Binned frequency and prob-ability density distribution plots of de-trital zircon grains from sample Kam-1 (Lower Cambrian) and Lbq-1 (Early Ordovician). conc—concordance; n—number of analyses with <10% discor-dance/total number of analyzed grains.

84 Linneman et al.

spe423-03 page 84

zircons vary between 0.1 and 1.0 (Tables 1–3), a range that is typical for zircon crystallized from magmas of intermediate to felsic composition (e.g., Hoskin and Schaltegger, 2003). From the Vesser complex ignimbrite Ves-1 we analyzed fi fteen zircon grains, which yielded a concordia age of 497 ± 2 Ma (Fig. 11B). Thus, the upper part of the Rollkopf Formation was most likely deposited during the uppermost Cambrian.

From the pebble-bearing rhyolitic tuffi te KArc-1, eighteen needle-shaped zircon grains were analyzed (Table 3). Nine of these yielded a concordia age of 486 ± 4 Ma, which is identical to the upper-intercept age defi ned by the four discordant analyses (Fig. 11C). The concordia age is interpreted to provide maximum age constraints for tuffi te deposition. In addition, one zircon yielded a concordant Archean age of 2.62 Ga (Table 3).

AGE OF SEDIMENTARY DEPOSTION

In each sample, the youngest concordant zircon age provides a maximum constraint for the deposition of the sampled unit. In the case of the Purpurberg quartzite and the Rothstein Formation,

the youngest ages are 558 ± 16 Ma and 552 ± 11 Ma, respec-tively. However, the uncertainty in the degree of concordance of Neoproterozoic-Paleozoic grains dated by the LA-ICP-MS method is relatively large, and results obtained from just a single analysis have to be interpreted with care. For example, a typical uncertainty of 2–3% (2σ) in 207Pb/206Pb for a Late Neoproterozoic grain (e.g., 560 Ma) relates to an absolute error on the 207Pb/206Pb age of 44–65 Ma. Thus, the youngest grains in both samples can be grouped in the ca. 570-Ma age population. Seven grains that defi ne this population in Pur-1 and Roth-1 defi ne concordia ages of 570 ± 4 Ma (mean squared weighted deviated [MSWD

C+E] =

0.59) and 566 ± 4 Ma (MSWDC+E

= 0.95), respectively. These ages are in agreement with a SHRIMP age of 566 ± 10 Ma for a tuff from the Rothstein Formation (Buschmann et al., 2001). It is therefore likely that the ca. 570-Ma grains in Pur-1 and Roth-1 originated from tuff horizons and that their crystallization ages closely date the depositional ages of the Purpurberg quartzite, Weesenstein Group and Rothstein Formation, respectively. In other words, the deposition of Weesenstein Group and the Roth-stein Formation took place shortly after ca. 570 and ca. 566 Ma,

520

440

400

360

320

280

0.04

0.05

0.06

0.07

0.08

0.35 0.45 0.55 0.65

206Pb238U

481 ±15 Ma(upper intercept age)

MSWD = 0.71

486 ±4 MaMSWDC+E = 0.81

to zero

KArc-1

data-point error ellipses are 2 σ

C


520

510

4800.077

0.079

0.081

0.083

0.085

0.60 0.62 0.64 0.66 0.68

Ves-1206Pb238U

497 ±2 MaMSWDC+E = 0.81

C+E = 0.77Probability

500

490

B


560

206Pb238U

Wett-1

207Pb/235U

543 ±4 MaMSWDC+E = 0.30

C+E = 0.97Probability

0.086

0.088

0.090

0.092

0.68 0.70 0.72 0.74 0.76

550

540

530

youngestzircongrains

only

A

Figure 11. Concordia plots showing LA-ICP-MS U-Pb ages impor-tant for the modeling of the Cadomian orogeny and the opening of the Rheic Ocean in the Saxo-Thuringian zone of the Bohemian Massif. Error ellipses are 2σ. For sample details see Tables 1 and 3. (A) Con-cordia age of 543 ± 4 Ma calculated from the ages of the fi ve youngest detrital zircon grains of microconglomerate sample Wett-1, placing the maximum age of deposition of the Lausitz Group close to the Precam-brian-Cambrian boundary (Lausitz antiform, Saxo-Thuringian zone). (B) Concordia age of 497 ± 2 Ma calculated from the ages of fi fteen magmatic zircon grains from rhyolithic ignimbrite sample Ves-1 from the Vesser complex. (C) Concordia age of 486 ± 4 Ma obtained from the ages of nine magmatic zircon grains from pebble-bearing felsic tuffi te sample Karc-1 from the base of the Ordovician in the southeast-ern part of the Schwarzburg antiform. The upper intercept age of 481 ± 15 Ma, defi ned by four discordant grains, overlaps with the concor-dia age. MSWD

C+E—mean squared weighted deviates of concordance

and equivalence.


spe423-03 page 85

respectively. A Neoproterozoic age for both units is also indicated by the intrusion of the Dohna granodiorite into the Weesenstein Group at 537 ± 7 Ma (Linnemann et al., 2000; Fig. 3) and the overlaying of the Rothstein Formation by the Zwethau Formation during the Atdabanian (Lower Cambrian) at ca. 534 Ma (Bus-chmann et al., 2006).

The youngest zircon subpopulation in sample Wett-1 yielded an age (543 ± 4 Ma) close to the Neoproterozoic-Cam-brian boundary. This age (Fig. 11A) is interpreted to provide a maximum depositional age for the Lausitz Group. However, shortly after its deposition, the Lausitz Group was deformed and subsequently intruded by voluminous granitoids at 539 ± 6 Ma (Linnemann et al., 2000). Given the uncertainties in the age deter-minations, deposition of the Lausitz Group can be constrained to a narrow time interval of ~10 m.y. (between 547 and 533 Ma) around the Precambrian-Cambrian boundary.

The control for the age of deposition of the Zwethau Forma-tion (Kam-1) comes from paleontological data. Based on trilo-bites and archaeocyatha, the formation is assigned to the Atda-banian, that is, the Lower Cambrian stage starting at ca. 534 Ma (Elicki, 1997, and references therein). The depositional age of the Langer Berg Formation (Lower Ordovician, Lbq-1) is controlled by trace fossils and regional lithostratigraphic correlation, with well-dated sections in the southeastern part of the Schwarzburg antiform (Linnemann, 1996). In both samples the youngest zir-con ages (Kam-1, ca. 535 Ma; Lbq-1, two grains, 498 ± 7 Ma) are very close to the biostratigraphic-controlled deposition age.

The age of 497 ± 2 Ma (Fig. 11B) for Ves-1 zircons is interpreted to date ignimbrite deposition within the upper part of the Rollkopf Formation in the Vesser complex. This part of the Rollkopf Formation is therefore Upper Cambrian, according to Gradstein et al. (2004), who place the upper boundary of the Middle Cambrian at 501 ± 2 Ma. In contrast, the lower part of the Rollkopf Formation is assigned to the Middle Cambrian, based on conventional U-Pb dating of zircon from a dacitic pyroclas-tite (508 ± 2 Ma) and from a gabbro (502 ± 2 Ma) that intrudes the units (Kemnitz et al., 2002; see also Fig. 6). At present no biostratigraphic or geochronological data are available for the Neuwerk Formation in the upper part of the Vesser complex. The overlying Hundsrück Group contains felsic volcanic rocks and highly mature quartzites that are interpreted to be Lower Ordo-vician, based on lithostratigraphic correlation (Bankwitz et al., 1992; Linnemann, 2003a; Fig. 6).

The age of 486 ± 4 Ma for seventeen zircon grains from sample KArc-1 is interpreted to closely date the deposition of the lithostratigraphic unit enclosing the tuffi te. The sample was taken from the level at which the boundary between the Cadomian basement and Lower Paleozoic overstep sequence is suspected. This transition interval is free of key fossils. In this section of the southeastern part of the Schwarzburg antiform no angular unconformity between Cadomian basement and the Lower Paleozoic sediments is observed. The age of the KArc-1 zircons suggest that the Cadomian basement was directly over-lain by highly mature sediments of lowermost Tremadocian age

(lowermost Ordovician; Fig. 6) and, thus, the entire Cambrian is missing.

PROVENANCE OF SEDIMENTS

The analyzed samples were selected to be representative of different successions of distinct ages. However, some care must be taken in the interpretation of the age spectra because a certain degree of sample bias cannot be excluded. Nevertheless, the U-Pb age spectra of the detrital zircons from samples Pur-1, Wett-1, Roth-1, Kam-1, and Lbq-1 show striking similarities (Figs. 8 and 10, Table 4), indicating that they display a common characteristic of the source area. Hence, variations among the samples are inter-preted as indicating variations in the source area. All fi ve samples predominantly contain Late Neoproterozoic (690–550 Ma; 40–83%) and Paleoproterozoic (2.2–1.8 Ga; 15–33%) grains with a smaller fraction of Neo- to Mesoarchean constituents (5–13%; Table 4). In addition, all samples contain a small fraction of ca. 1000- to 900-Ma (1–7%) grains. Only the three Neoproterozoic sediments contain Mid-Neoproterozoic (790–700 Ma; 3–8%) zircons, and Paleoarchean (3–8%) components are present only in Pur-1 and Lbq-1. A common feature of all samples is an “age gap” between 1.75 and 1.0 Ga, which is typical of a Cadomian and/or west African provenance and is diagnostic in distinguish-ing it from East Avalonia and Baltica (e.g., Nance and Murphy, 1994; Friedl et al., 2000). This age gap is in agreement with the characteristic clusters of Paleoproterozoic ages in the interval 2.17–1.78 Ga. Such ages are typical of the western part of the Gondwana supercontinent, which was affected by abundant mag-matic intrusions (ca. 2.2–1.8 Ga) during the Eburnean orogeny (West African craton). Furthermore, Neo- to Mesoarchean zircon ages and, in the case of Pur-1 and Lbq-1, additional Paleoarchean grains, point to recycling of magmatic rocks formed during the Liberian and the Leonian orgenies, respectively. Both orogenies affected the West African craton during the Archean.

The overall dominance of Late Neoproterozoic zircon ages with apparent clusters at ca. 570, ca. 590, ca. 620–610, ca. 640, and ca. 660 Ma point to the fact that the most important source of sedimentary detritus (>55%) was the active magmatic arc of the Cadomian belt (ca. 700–550 Ma; e.g., Nance et al., 2002; Mur-phy et al. 2004; Linnemann et al., 2000, 2004). Taking all 165 Neoproterozoic zircon ages (700–550 Ma) into consideration, the main magmatic activity of this Cadomian arc took place at ca. 615, ca. 590, and ca. 570 Ma (28, 27, and 21%, respectively).

Orthogneisses of Mid-Neoproterozoic protolith age (ca. 755–700 Ma) have been described from the Armorican Massif (Samson et al., 2003) and the Anti-Atlas orogen in Morrocco (D’Lemos et al., 2006). Based on Hf and Nd isotopes these have been interpreted as remnants of an earlier, independent arc sys-tem. Such ages are relative rare in the Avalonian-Cadomian belt. Our results suggest that such sources were present only during the Neoproterozoic and were absent during younger sedimentation.

All samples contain a small fraction of grains with ages close to the Neo- to Mesoproterozoic boundary. Until recently,

86 Linneman et al.

spe423-03 page 86

such “Grenville” ages were interpreted as being derived either from the Amazonian craton (e.g., Friedl et al. 2000; Hegner and Kröner 2000; Fernández-Suárez et al., 2002) or from the Grenville orogenic belt (e.g., Nance and Murphy, 1994). Gren-ville ages typically fall in the range 1.25–1.0 Ga (e.g., Keppie et al., 1998), and an Amazonian provenance is characterized by various Mesoproterozoic age peaks in the 1.8- to 1.0-Ga inter-val (e.g., Nance and Murphy, 1994; Friedl et al., 2000). These ca. 1.05- to 0.9-Ga zircon ages are relatively rare but have been described from various localities within Cadomia (Gebauer et al., 1989; Fernández-Suárez et al., 2002; Gehmlich, 2003; Friedl et al., 2004). They therefore represent a typical Cadomian detrital zircon subpopulation and most likely also have a west African origin. The presented zircon ages strongly suggest a provenance

of the investigated Neoproterozoic rocks from the margin of the West African craton (Fig. 12).

PLATE-TECTONIC MODEL

The data set presented above provides several cornerstones that must be taken into account in the reconstruction of the Neoproterozoic to Cambro-Ordovician evolution of the Saxo-Thuringian zone and adjoining crustal units of the Bohemian Massif. First, all investigated units contain considerable quanti-ties of Archean, Paleoproterozoic, and Neoproterozoic zircons, which provide evidence of intense crustal recycling (Linnemann et al., 2000, 2004; Drost et al., 2004; this study). The detrital age spectra point to a west African provenance and exclude an Ama-

South

pole

Aval

onia

n-

Cad m ano

iA ict ve M r na gi

ca. 570 Ma

Peri Gondwana

-

Per

i-G

on

dw

ana

Ura

ls

E-Ava

lonia

-Aal

ona

Wv

i

Co

lar

ina

Florida

Iber

ia

AM

FMC

Turkish plateAegean

Dobrogea

SXZ T UB

r-A

s

"Poto

lp"

0.55-0.650.9-1.1

1.65-1.852.45-2.7 Ga

*2

0.54-0.71.8-2.22.7-2.9

3.1-3.4 Ga *1

0.54-0.71.0-1.35

1.45-1.752.5-3.1 Ga

*3

0.9-1.21.3-2.2

2.5-2.853.0-3.2 Ga

*4

a

nw

n

Est Go

da

a

eo

dana

Wst G

nw

Yu

cata

n

Oax

aia

qur

isC

ot

Cratons (Archean-Paleoproterozoic)

1.1 - 1.3 Ga Megashear event in Amazonia

Mesoproterozoic mobile belts (Grenville and related events)

Neoproterozoic mobile belts of Gondwana(Pan-African and related events)

Neoproterozoic mobile belts of peri-Gondwana(Cadomian and related events)

CADOMIA

Figure 12. Paleogeography of the Cadomian-Avalonian active margin and related major peri-Gondwanan terranes at ca. 570 Ma. AM—Armori-can Massif; FMC—French Massif Central; SXZ—Saxo-Thuringian zone (part of the Bohemian Massif); TBU—Teplá-Barrandian unit (part of the Bohemian Massif). Numbers in circles: zircon ages from the cratons in Ga. *1—from the compilation of Nance and Murphy (1994 and refer-ences therein); *2—from Avigad et al. (2003); *3—from Schneider Santos et al. (2000); *4—from the compilation of Zeh et al. (2001). Modifi ed after Nance and Murphy (1994, 1996), Linnemann et al. (2000, 2004), Murphy et al. (2000), Linnemann and Romer (2002), Nance et al. (2002); paleogeography of the Gondwanan continental plates after Unrug (1996).


spe423-03 page 87

zonian and/or Baltic source (Drost et al., 2004; Linnemann et al. 2004; this study). Second, the zircon age spectra indicate that some Late Neoproterozoic sediments were deposited at about the same time (ca. 570 Ma), during, and after intense magmatic activity in the adjacent arcs. Third, most sedimentary basins were deformed between ca. 570 and 540 Ma and intruded by volu-minous granitoid plutons at ca. 540 Ma. The absence of Cado-mian high-grade or high-pressure regional metamorphic rocks like granulite and eclogite suggests that this structural-magmatic event took place without major thickening of the crust and with-out subduction of continental crust (Linnemann et al., 2000). Electron microprobe dating of metamorphic monazite grains from the Teplá-Barrandian unit yielded Th-U-Pb model ages of 540 ± 16, 542 ± 13, and 551 ± 19 Ma, which Zulauf et al. (1999) related to low-pressure/high-temperature metamorphism. Fourth,

the generation of Lower to Middle Cambrian rift-related sedi-ments, Upper Cambrian (ca. 500 Ma) MOR-related mafi c rocks (Bankwitz et al., 1992; Kemnitz et al., 2002; this study) and thick Lower Ordovician successions with high subsidence rates indi-cate the formation of a rift-drift succession in Cambro-Ordovi-cian time (Linnemann and Romer, 2002; Kroner et al., 2003; Linnemann et al., 2004).

Cadomian Back-Arc Basin Evolution

The oldest rocks of the Saxo-Thuringian zone are sediments deposited at ca. 570–565 Ma. Rock units belonging to this age interval make up the Weesenstein and Clanzschwitz groups as well as the Altenfeld and Rothstein Formations (Figs. 3 and 13). The Altenfeld Formation of the Schwarzburg antiform comprises

debris

debris

Strike-slip basinand spreadingzones in the

backarc basin

RothsteinFormation(Roth-1:

566+/-4 Ma)

ClanzschwitzGroup

WeesensteinGroup

Purpurbergquartzite

(Pur-1: 570+/-4 Ma)

AltenfeldFormation

Continent(crust of the

West African craton)

Transitional crust:early Cadomian arc

(c. 600-650 Ma)

Oblique vectorof subduction

MOR-basalts,andesites andhydrothermalblack cherts

closed strike-slipbasin: redepositionof sediments and

arc-related igneousrocks

Cadomian arc(late stage,

c. 550-590 Ma)

Intra-arc basin

stretched and thinnedcontinental and arc crust

byU

lLi

nem

ann

206

fn

0

Cadomian backarc basinc. 590-560 MaEarly Miocene

Euian

rasate

Pl

pJa

aArc

n

f cPaci i Plate

stretchedcontinental

crustoceanic crust

apanJ

Sea

N

debris

Figure 13. Model for the plate-tectonic development of the Cadomian back-arc basin at ca. 590 and 560 Ma, based on data derived from the Saxo-Thuringian zone (Bohemian Massif). Back-arc basin consists of a continentward passive margin, represented by the Weesenstein and Clanzschwitz groups, and an arcward margin, characterized by more strongly stretched continental crust and the accumulation of predominantly arc-derived debris. The back-arc is documented by MOR-related rocks and hydrothermal black cherts recorded in the Altenfeld and the Rothstein formations. Inset: Sketch of analogous plate-tectonic confi guration represented by the opening of the Japan Sea in the western Pacifi c region during the Early Miocene (after Jolivet et al., 1992). The back-arc basin of the Japan Sea is largely fl oored by stretched continental crust.

88 Linneman et al.

spe423-03 page 88

similar facies to those of the Rothstein Formation (black cherts, mafi c igneous rocks), suggesting a similar age and plate-tectonic setting of deposition (Fig. 13). In the same way the Clanzschwitz Group can be correlated with the Weesenstein Group (Pur-1).

We assume that all of these units were deposited in a back-arc basin, which predominantly consisted of thinned continental crust and was fl anked by a magmatic arc to the “north” and by a cratonic source to the “south” (Linnemann et al., 2000; Bus-chmann et al., 2001; Figs. 3 and 13). Back-arc spreading at ca. 570 Ma is best documented by the Rothstein Formation (Bus-chmann, 1995). Field data and geochemical information sug-gest that the 566 ± 10-Ma-old Rothstein Formation comprises a low-grade metamorphic suite of intrusive and effusive enriched mid-ocean ridge basalts (E-MORB), andesites, calc-alkaline metabasalts, and subordinate alkaline metabasalts (Buschmann, 1995; Buschmann et al., 2001). The submarine effusive character of these rocks is indicated by pillow structures that may have formed during seafl oor spreading. The submarine character is additionally supported by black cherts, which are assumed to be the product of hydrothermal activity at a spreading center that caused alteration of the submarine volcanic and sedimentary rocks (Fig. 4A). According to Buschmann (1995), deposition of the Rothstein Formation was accompanied by strike-slip faulting that produced submarine pull-apart basins and led to the re-sedi-mentation of older unconsolidated sediments. A similar age and tectonic regime is assumed for the Altenfeld Formation.

In contrast to the Rothstein and Altenfeld formations, the Weesenstein and the Clanzschwitz groups were most likely deposited at the passive margin of the back-arc basin, the exis-tence of which is indicated by (1) Nd-model ages for the sedi-ments in the range ca. 2.1–1.5 Ga (Linnemann and Romer, 2002), (2) abundant Paleoproterozoic detrital zircon ages (Linnemann et al., 2004; this study), and (3) the presence of highly mature sedi-ments like the Purpurberg quartzite (Linnemann, 1991; Fig. 13).

The existence of a Cadomian magmatic arc can deduced from the geochemical signatures of the Late Neoproterozoic sediments (Buschmann, 1995; Linnemann and Romer, 2002; Drost et al., 2004). These sediments have a felsic provenance pointing to a relatively mature continental arc with a relatively thick root zone.The main phase of arc magmatism occurred between ca. 560 and 600 Ma (Linnemann et al., 2004; this study). Comparable ages and arc-related igneous rocks are also described from the Avalon-ian part of the Bohemian Massif (Finger et al., 2000; Friedl et al. 2004; Fig. 2). Relatively small remnants of the Cadomian arc are known from the Armorican Massif and Iberia. Also in the Bohe-mian Massif arc remnants sensu stricto are scarce (e.g., Kríbek et al., 2000). It therefore appears that the main part of the Cadomian arc and its Avalonian counterpart are preserved in the Avalonia microcontinent (Murphy et al., 2006), whereas the main part of the back-arc basins remained in Cadomia. This arrangement is impor-tant to the subsequent opening of the Rheic Ocean (see below).

Figure 13 shows a possible reconstruction of the Cadomian back-arc basin in the Saxo-Thuringian zone, with deposition of the passive margin sequences of the Weesenstein and Clanzschwitz

groups on the southern fl ank. The Rothstein and the Altenfeld formations are located in the interior portion of the back-arc basin within the external domain of the Saxo-Thuringian zone to the north (Fig. 2). We interpret the present geographical arrangement as refl ecting the original paleoposition on the west African mar-gin. Sample Pur-1 (Weesenstein Group) from the passive margin sequence contains ~40% Late Neoproterozoic detrital zircons derived from the Cadomian arc, which is considerably less than their abundance in Roth-1 from the Rothstein Formation (66%). In addition, the two samples differ in their Neoproterozoic age spectra, ~60% of Late Neoproterozoic grains in Pur-1 falling in the age range 670–600 Ma, whereas ~60% in Roth-1 fall in the range ca. 590–560 Ma. This difference suggests that in the source area of the passive margin, sequence remnants of an earlier stage of the Cadomian magmatic arc were exposed. This arc may rep-resent the transitional zone between the craton and the stretched crust underlying the basin fl oor of the back-arc basin (Fig. 13). Consequently, we assume this early arc stage (ca. 670–600 Ma) was characterized by a Cordilleran-type active margin with sub-duction of the oceanic plate directly under the craton.

The Cadomian back-arc basin probably opened into an expanded marginal basin to allow for the differentiation of its deposits into various facies patterns. The age of granitoid peb-bles (577 ± 3 and 568 ± 4 Ma; Linnemann et al., 2000) from the Weesenstein and Clanzschwitz groups suggests rapid exhuma-tion of granitoids intruded in the source area during or shortly before opening of the back-arc basin. The latter likely took place within a strike-slip regime, with the development of small sub-basins acting as local suppliers of sediments, including material derived from the underlying stretched crust (Fig. 13). On the basis of similar relationships in Avalonia, Nance and Murphy (1994) proposed a model in which the oblique vector of subduc-tion beneath the arc led to strike-slip motions in the back-arc basin. The concept of oblique subduction and its effects in the hinterland, combined with our fi eld observations, is incorporated into the model in Figure 13.

Cadomian Retroarc Basin

The largest part of the weakly metamorphosed and well-pre-served Late Neoproterozoic sediments of the Saxo-Thuringian zone is represented by the Lausitz Group (Wett-1; Lausitz anti-form), the Leipzig Formation (North Saxon antiform), and the Frohnberg Formation (southeastern part of the Schwarzburg antiform) (Figs. 2 and 3). These units are positioned between the deposits of the inner back-arc basin and the passive margin (Figs. 2 and 3) and clearly differ in their fl ysch-like character from the sedimentary units discussed above. They are characterized by monotonous series of dark-gray graywacke turbidite inter-calations of conglomerates and microconglomerates that often contain fragments of granitoids, metasediments, and black cherts (Fig. 4D). Frequent black chert fragments indicate their deriva-tion, in large part, from eroded material derived from the inner back-arc basin. Given their similarity in lithology, sedimentation


spe423-03 page 89

regime, spatial distribution, and detrital modes, a comparable depositional age is assumed for the Leipzig and Frohnberg for-mations and the Lausitz Group. Depostion most likely took place at the Precambrian-Cambrian boundary, ~20–30 m.y. after the opening of the back-arc basin, as inferred from Wett-1 zircon ages and the intrusion of younger granites (see above).

Sedimentary structures and paleoseismic features, such as water-escape structures (Fig. 4E), soft pebbles, and seismites, suggest rapid sedimentation (Linnemann, 2007). As shown in Figure 14, we interpret the Lausitz Group and the Leipzig/Frohn-berg formations to be parts of a Cadomian retroarc basin or fore-land basin. In our model this basin was formed during closure of the back-arc basin in response to the collision of the Cadomian

arc with the West African craton. Only the inner part of the retro-arc basin was folded and thrusted, which explains why the more northerly portions of the Lausitz Group and the Leipzig Forma-tion were deformed before intrusion of the ca. 540-Ma granitoids (Linnemann et al., 2000). An angular Cadomian unconformity between Late Neoproterozoic rocks and Cambro-Ordovician deposits is documented from different sections of these units (Linnemann and Buschmann, 1995a,b). However, the zircon age of 486 ± 4 Ma from pyroclastic sediments (KArc-1) of the Frohn-berg Formation point to an Early Ordovician onset of Paleozoic sedimentation in the sections from the southeastern part of the Schwarzburg antiform. Cambrian strata are missing here, and the Cadomian unconformity is not an angular one. Instead, it is a

Cadomianretroarc basinc. 545-540 Ma

Retroarc basin

Remnantbasin

inner

outer

Magmatic andanatectic event

at c. 540 Ma

Fold-and thrust belt

FrohnbergFormation

(upper section)

Continent(cratonic crust)with chemical

weatheringsurface

Slab break-off

ol ed a hr tF d nd t us edr ks o heoc f t

a omi nC d aba a s nck rc ba i

Ul

iem

nn00

byf L

nna

26

FrohnbergFormation

(lower section)

Change to atransform margin

Erosion of the black chert-bearingRothstein and Altenfeld formations

in the fold- and thrust belt

LausitzGroup

(Wett-1:543+/-2 Ma)+Leipzig fm.

Figure 14. Model for the plate-tectonic evolution of the Cadomian retroarc basin between ca. 545 and 540 Ma, based on data from the Saxo-Thuringian zone. There is no Cadomian angular unconformity on the continentward outer margin of the retroarc basin because Late Neoprotero-zoic sediments were unaffected by deformation (e.g., upper section of Frohnberg Formation in southeastern part of Schwarzburg antiform). In contrast, closer to the fold-and-thrust belt in the inner part of the retroarc basin, the sediments are deformed and consequently an angular uncon-formity is developed between Neoproterozoic retroarc sediments and overstepping Cambro-Ordovician strata (e.g., Cadomian unconformities at top of the Lausitz Group and Leipzig Formation). fm—formation.

90 Linneman et al.

spe423-03 page 90

disconformity or a simple sedimentation gap (paraconformity), without the occurrence of deformation between the under- and overlying strata. Thus, the undeformed Frohnberg Formation is interpreted to have been deposited in a more distal position rela-tive to the fold-and-thrust belt and more proximal to the cratonic hinterland, whereas the deformed Lausitz Group and Leipzig Formation were situated closer to the colliding arc (Fig. 14).

In contrast to the lower part of the Frohnberg Formation, which is composed mainly of thick-bedded graywackes, the ~100-m-thick upper part was likely deposited in a shallower marine environment (Linnemann, 2003b). This observation sug-gests termination of the retroarc basin regime and the onset of deposition in a remnant basin located in front of the outer retro-arc deposits (Fig. 14). The very topmost quartzite bed of the sec-tion, known as “Basisquarzit” (=basal quartzite), is tradionally interpreted as the base of the Paleozoic overstep sequence (von Gaertner, 1944). It is, however, more likely that this quartzite rep-resents the fi nal bed of a continuous upward-thickening section of the Neoproterozoic remnant basin.

The Cadomian retroarc basin and the related remnant basin were short-lived depositional systems. Based on the youngest detrital zircon ages of Wett-1 (543 ± 4 Ma; Fig. 11A) and the age of the Lausitz granitoid complex (539 ± 6 Ma; Fig. 3), which intrudes these sedimentary units, the ages and time spans of these systems can be confi ned to a time interval of <12 m.y. at the end of the Neoproterozoic and in the earliest Cambrian.

Most Late Neoproterozoic sedimentary were intruded by voluminous granitoids at ca. 540 Ma (Linnemann et al., 2000; Gehmlich, 2003; Tichomirowa, 2003; Fig. 3). The largest exposed body is the Lausitz granitoid complex, which covers an area of ~100 × 50 km2. For this complex, a minimum granitoid volume of ~5000 km3 can be calculated, assuming a thickness of only 1 km. Most granitoids were likely derived from melting of the Late Neo-proterozoic graywackes or similar units, because they contain large numbers of inherited zircons with age spectra comparable to those in the sediments (Linnemann et al., 2000, 2004; Gehmlich, 2003; Tichomirowa, 2003). This interpretation is supported by geo-chemical data and graywacke xenoliths in the granitoids (Hammer, 1996). These ca. 540-Ma granitoids record a relatively short-lived regime of high levels of heat fl ow, which we attribute in our model to slab break-off of the subducted oceanic plate (Fig. 14).

All the processes summarized in Figures 13 and 14, from the early stages of a Cadomian magmatic arc (ca. 650–600 Ma), through opening of the Cadomian back-arc basin and its closure during arc-continent collision with subsequent formation of a ret-roarc basin, to the magmatic-anatectic event at ca. 540 Ma, corre-spond to our present understanding to the Cadomian orogen that formed at the margin of the West African craton.

Opening of the Rheic Ocean

There is no sharp break between the geological history linked to the Cadomian orogen and that of the Cambro-Ordovi-cian, which fi nally led to the opening of the Rheic Ocean. Instead,

the latter is viewed as a logical continuation of the geological his-tory of the dying marginal orogen. Nance and Murphy (1996) and Nance et al. (2002) proposed a Cordilleran model for the fi nal stages of the Avalonian-Cadomian orogen analogous to the Cenozoic history of ridge-continent collision in the area of Baja California in the eastern Pacifi c. Such a model would explain both the geodynamic change from subduction-related processes to the opening of a new ocean and the excision of a long slice of continental crust, like that which formed the microcontinent of Avalonia. We have adapted these ideas to explain the plate-tectonic setting of the Saxo-Thuringian zone during the Cambro-Ordovician. After ridge-continent collision, slab break-off was triggered at ca. 540 Ma by the switch from an active margin to a transform margin setting (Fig. 15, inset).

Cambrian sediments in the Saxo-Thuringian zone are restricted to the Lower and Middle Cambrian, with the onset of sedimentation occurring in the Atdabanian at ca. 530 Ma (Elicki, 1997). These units are characterized by carbonates with archaeocyatha, siliciclastic sediments, and red beds. The last were likely derived from erosion of laterite horizons generated on the denuded Cadomian orogen and the cratonic hinterland at ca. 540–530 Ma (Linnemann and Romer, 2002). These occurrences suggest a general uplift of the Cadomian orogen that was prob-ably due to the rapid changes in plate-tectonic setting. In addi-tion, the laterites and the occurrence of archaeocyatha point to deposition at low paleolatitudes.

The overall change of the plate-tectonic regime is refl ected by the onset of Cambrian sedimentation. Detritus of the Cam-brian deposits was predominantly (~80%) derived from the Cadomian orogen, as inferred from the age spectrum of Kam-1. The plate-tectonic setting may therefore have been similar to that of the present-day Basin and Range Province lying close to Baja California and the San Andreas fault (Fig. 15). In this way, stretching and thinning of the Cadomian crust and transcurrent faulting induced by the activity of the transform margin may have led to the opening of a rift basin fi lled with Lower and Middle Cambrian sediments. As a result, the Cadomian orogen became largely denuded. The rift basin likely developed on the side of the faulted and thrusted orogen, because this location would have been more sensitive to tectonic reactivation than the cratonic hin-terland. The interplay between the more stable cratonic hinter-land and the weaker Cadomian crust is thought to have led to asymmetric rifting (Fig. 15).

Upper Cambrian sediments are relatively scarce in the Saxo-Thuringian zone, and fossiliferous deposits of this age are unknown. However, the lower and upper part of the Rollkopf Formation from the Vesser complex were deposited during the Middle and Upper Cambrian, respectively (see above). This unit belongs to the external domain of the Saxo-Thuringian zone, refl ecting a paleoposition on the outer margin of the eroded and recycled Cadomian orogen. The Vesser complex is dominated by MOR-related igneous rocks associated with metasediments (Bankwitz et al., 1992; Figs. 2 and 6). In our view, this complex records the incision of an oceanic ridge that collided with the


spe423-03 page 91

periphery of the Cadomian orogen in a situation similar to pres-ent-day Baja California (inset of Fig. 16). Thinning of the litho-sphere and upwelling asthenosphere led to enhanced heat fl ow in the upper lithosphere and the generation of Vesser magmatism. In our model the Vesser complex formed between the outer and inner zone of the asymmetric rift basin, as this location represents its weakest part (Fig. 16). The outer part, the former continental arc, was characterized by relatively thick crust, ongoing subsidence, and Upper Cambrian sedimentation, whereas the inner part, the former Cadomian back-arc basin, was more strongly affected by lithospheric thinning caused by uplift and upwelling of the asthe-nosphere (Fig. 16). Asymmetric rifting typically shows uplift of the remaining, thinned, lower plate and subsidence of the depart-ing heavier upper plate (Wernicke, 1985; Coward, 1986). This asymmetry would explain the ongoing Cambrian sedimentation

on the upper plate, which would later become a part of Avalonia or a related terrane, and the absence of Upper Cambrian deposits on the lower plate, which represents the Cadomian realm at the periphery of the West African craton. This scenario is in agree-ment with the lack of Upper Cambrian sediments in the Saxo-Thuringian zone and the high maturity of Lower Ordovician deposits resulting from intense chemical weathering processes during the Upper Cambrian.

Lower Ordovician deposits in the Cadomian part of cen-tral and western Europe are characterized by thick and wide-spread sandstone deposits, frequently metamorphosed to quartzites. The most prominent example is the ≤700-m-thick Armorican quartzite of the Armorican and Iberian massifs. Its equivalents in the Saxo-Thuringian zone are the quartzites of the 3000-m-thick Frauenbach and Phycodes groups from the

Asymmetric rift basinduring the Lower and

Middle Cambrianc. 530-500 Ma

Rift basin(asymmetric

rifting)

RiftedCadomianbasement

Continent(cratonic crust)

FormerCadomian

continental arc

Lower to MiddleCambriansediments

byU

lL

nem

nn2

0f

in

a0

6

Zwethau,Tröbitz,

& DelitzschFormations

Meandetachment

level

Transform margin

San Andreas Fault

Basin and Range

10 Ma

N

Figure 15. Model for the formation of the asymmetric rift basin during the Lower to Middle Cambrian between ca. 530 and 500 Ma in the Saxo-Thuringian zone. The geological setting (see inset) is assumed to be similar to that of the Basin and Range province of North America 10 m.y. ago. Modifi ed from Atwater (1970), Christiansen and Lipman (1972), Dickinson (1981), Condie (1989), and Nance et al. (2002).

92 Linneman et al.

spe423-03 page 92

southeastern part of the Schwarzburg antiform (Fig. 6). Quartz-ites of the Langer Berg Formation (Lbq-1) and those from the Hundsrück Group (Vesser complex) are their stratigraphic equivalents (Fig. 6). These deposits overstep in places Lower to Middle Cambrian strata (e.g., drill holes Heinersdorf 1 and 2; Wucher, 1967; Linnemann et al., 2000) and in other cases over-lie directly the Cadomian basement, as in the Hohe Dubrau area in the Lausitz antiform (Linnemann and Buschmann, 1995b). Both forms of the Cadomian unconformity are also reported from the Armorican Massif and different parts of Iberia. It is therefore likely that rifting culminated in the Upper Cambrian, with the formation of rift shoulders, tilted blocks, and/or horsts and grabens, such that, in some places the Lower to Middle Cambrian is preserved, whereas in others the underlying Cado-mian basement is exposed.

Extension over the entire paleolandscape and the enormous thickness of the Lower Ordovician overstep sequences classify these siliciclastics as post-rift sediments or deposits of a rift-drift transition. These sedimentary rocks must have been linked to considerable tectonic activity and thermal subsidence, resulting in large systems of detachment faults and escarpments on the sur-face. Lbq-1 (Langer Berg Formation) shows a very similar pre-Ordovician zircon age spectrum to those of the Neoproterozoic deposits (Table 4). The signifi cant number of Paleoproterozoic and Archean grains suggests that rift-related breakaway faults extended into the cratonic hinterland (Fig. 17). In addition, Cado-mian basement and Cambrian igneous rocks were either avail-able to erosion or their zircons were distributed in the weather-ing crust formed during the Upper Cambrian and recycled by the Lower Ordovician transgression.

Upper Cambrian:Incision of theoceanic ridge

c. 500-490 Ma

Uplift

Vessercomplex:bimodal

magmatism& MOR-relatedrocks

(Ves-1:497+/-2 Ma)

Continent(cratonic crust)

Inner Zoneof the

rift basinSubsidenceand ongoing

Upper Cambriansedimentation

Uplift, chemical weatheringand gap during

the Upper Cambrian

Uf

byl

Linn

eman

n20

06

Transform margin

Dehydration& new melts

Incision of theoceanic ridge

High heat flow and magmaticevent caused by thinning

of lower crust and upwellingof the asteosphere

Baja CaliforniaJuan de Fuca Rise

3 Ma

OuterZoneof the

rift basin

N

Figure 16. Plate-tectonic model for the opening of the Rheic Ocean during the Upper Cambrian between ca. 500 and 490 Ma in the Saxo-Thuringian zone. Ocean opening is assumed to have been caused by the oblique subduction of an oceanic ridge similar to the present plate-tectonic situation (see inset) on the west coast of North America. MOR—mid-oceanic ridge. Modifi ed from Atwater (1970), Christiansen and Lipman (1972), Dickinson (1981), Condie (1989), and Nance et al. (2002).


spe423-03 page 93

Magmatic rocks with an age of ca. 490–480 Ma are widely distributed in the Saxo-Thuringian zone. They range from large plutons (Rumburk granite, Lausitz antiform; Figs. 2 and 3) to subvolcanic porphyroids (Bärentiegel, Schwarz-burg antiform; Fig. 3) and various pyroclastics (e.g., Wurzel-berg tuffi te; Linnemann et al., 2000). An example of the last is sample KArc-1 (“Konglomeratische Arkose”), dated at 486 ± 4 Ma (Figs. 3, 11A). This magmatic event represents the fi nal rift-related magmatism (Fig. 17). After ca. 480 Ma, the Saxo-Thuringian zone is characterized by tectonic and magmatic qui-escence and monotonous shelf sedimentation. We interpret this zone to be the passive margin of the Rheic Ocean, which had

opened as a result of the separation of Avalonia or a related ter-rane (Fig. 18).

The geodynamic evolution outlined above has been deduced as far as possible from fi eld geology, zircon dating, and petrographic and geochemical data. We have attempted to illus-trate the way Cadomian orogenic processes may have operated and have compiled evidence supporting the idea that large parts of the Cadomian magmatic arc are now present in Avalonia or a related terrane, while the back-arc and the retroarc basins remained in Cadomia. We believe the long-lasting subduction processes that produced the arc and related basins were termi-nated by ocean closure in combination with ridge-continent

Rift and drift transition: Openingof Rheic ocean and formation

of passive marginc. 490-480 Ma

Tuffite(KArc-1:

486+/-4 Ma)

Oceanic crust

Oceanic ridge

BuriedVesser

complex

Lower to MiddleOrdovician

overstep sequence

Final rift-relatedmagmatismat c. 490 Ma

Southern passive margin sequenceoverlying Cadomia

Opening of theRheic ocean

Remnants of Lowerto Middle Cambrian

byU

lfLi

nnem

an2

06n

0

Baja CaliforniaJuan de Fuca Rise

3 Ma

Northern passive margin sequenceoverlying driftedarc (Avalonia orrelated terrane)

N

Unconformities onNeoproterozoic and

L.-M. Cambriansediments

Figure 17. Plate-tectonic model for the fi nal opening of the Rheic Ocean and the formation of passive margins at ca. 490–480 Ma. The northern terrane that separated from the Gondwanan margin (Cadomia) could be part of Avalonia or a correlative terrane. Note the different unconformi-ties between Neoproterozoic/Cambrian, Neoproterozoic/Ordovician and Cambrian/Ordovician strata, the general overstep of Lower Ordovician shallow marine sediments, the burial of the Vesser complex, and the renewed exhumation of cratonic crust in the hinterland. Inset shows analo-gous plate tectonic situation in part of the Basin and Range province of North America at ca. 3 Ma. Modifi ed from Atwater (1970), Christiansen and Lipman (1972), Dickinson (1981), Condie (1989), and Nance et al. (2002).

94 Linneman et al.

spe423-03 page 94

collision. We have also tried to show that Cadomian oroenic processes and the subsequent opening of the Rheic Ocean were closely related to each other.

CONCLUSIONS

Sediment provenances and magmatic events of Late Neopro-terozoic (Ediacaran) and Cambro-Ordovician rock assemblages of the Saxo-Thuringian zone have been constrained by new LA-ICP-MS U-Pb ages from detrital zircons of fi ve sandstones and magmatic zircons in an ignimbrite and one tuffi te. These geo-chronological results, in combination with the analysis of plate-tectonic setting constrained from fi eld observations, sedimento-logical and geochemical data, and trends in basin development, have been used to reconstruct Cadomian orogenic processes dur-ing the Late Neoproterozoic and the earliest Cambrian. A contin-uum between Cadomian orogenesis and the opening of the Rheic Ocean in the Cambro-Ordovician is supported by this data set.

The early stage of Cadomian evolution is characterized by a Cordilleran-type continental magmatic arc, which was estab-lished at the periphery of the West African craton between 650 and 600 Ma. Subsequently, at ca. 590–560 Ma, a back-arc basin was formed behind the Cadomian magmatic arc. The formation of this basin was caused by crustal stretching in a strike-slip regime, which is similar to that presently observed in the Japan Sea of the western Pacifi c. Following collision of the Cadomian magmatic arc with the cratonic hinterland, the back-arc basin was closed between ca. 545 and 540 Ma. At this time a short-lived Cadomian retroarc basin was formed. Subsequently, a mid-oceanic ridge was subducted underneath the Cadomian orogen. This process may have been accompanied by slab break-off of the subducted

oceanic plate, which resulted in increased heat fl ow, refl ected in voluminous magmatic and anatectic events culminating at ca. 540 Ma. The subsequent oblique incision of the oceanic ridge into the continent caused the formation of rift basins during the Lower to Middle Cambrian (530–500 Ma). This plate-tectonic scenario is assumed to have developed in a setting similar to that of the Baja California area ca. 3–10 Ma ago. This process contin-ued from the Middle to the Upper Cambrian (ca. 500–490 Ma) and fi nally caused the opening of the Rheic Ocean, an event doc-umented by thick Lower Ordovician siliciclastic sediments and a fi nal rift-related, bimodal magmatic event at ca. 490–480 Ma.

ACKNOWLEDGMENTS

<FLUSH>Prof. Dr. Gerhard Brey, Dr. Heidi Höfer, Jan Heli-osch, Kai Klama, and Dr. Yann Lahaye (Institut für Geowis-senschaften, Facheinheit Mineralogie, Universität Frankfurt am Main) are thanked for their help and fruitful discussions. We thank Damian Nance (Athens, Ohio, United States) for editorial handling and improving the language, and Dr. Jana M. Horák (Cardiff, United Kingdom), Dr. Stanislaw Mazur (Wroclaw, Poland) and Dr. Armin Zeh (Würzburg, Germany) for their crit-ical reviews and inspiring discussions. Funding was provided to AG by the German Science Foundation (DFG; GE 1152/2-2). This paper is a contribution to the International Geological Cor-relation Program Project 497—“The Rheic Ocean: Its origin, evolution and correlatives” (http://www.snsd.de/igcp497/).

REFERENCES CITED

Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonic evo-lution of western North America: Geological Society of America Bulletin, v. 81, p. 3513–3536.

Avigad, D., Kolodner, K., McWiliams, M., Persing, H., and Weissbrod, T., 2003, Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating: Geology, v. 31, p. 227–230, doi: 10.1130/0091-7613(2003)031<0227:OONGCS>2.0.CO;2.

Bankwitz, P., Bankwitz, E., Kramer, W., and Pin, C., 1992, Early Paleozoic bimodal volcanism in the Vesser area, Thuringian Forest, eastern Germany: Zentralblatt für Geologie und Paläontologie, Teil I, v. 9/10, p. 1113–1132.

Barrois, C., 1899, Sketch of the geology of Brittany: Proceedings of the Geolo-gists’ Association. Geologists’ Association, v. 16, p. 101–132.

Bertrand, L., 1921, Historie de la formation du sous-sol de la France. 1. Les anci-ennes mers de la France et leurs dépôts: Paris, Ernest Flammarion, 190 p.

Bowring, S.A., Ramezani, J., and Grotzinger, J.P., 2003, High-precision U-Pb geochronology and the Cambrian-Precambrian boundary, in Geological Association of Canada, NUNA Conference 2003, New frontiers in the fourth dimension: Generation, calibration and application of geological time scales, 15–18 March, Mont Tremblant, Quebec.

Bunel, H., 1835, Observations sur les terrains intermédiaires du Calvados: Mémoires de la Société Linnéenne de Normandie, v. 5, p. 99–100.

Buschmann, B., 1995, Geotectonic facies analysis of the Rothstein Formation (Neoproterozoic, Saxothuringian Zone, east Germany) [Ph.D. thesis]: Freiberg, TU Bergakademie Freiberg, 122 p.

Buschmann, B., Nasdala, L., Jonas, P., Linnemann, U., and Gehmlich, M., 2001, SHRIMP U-Pb dating of tuff-derived and detrital zircons from Cadomian marginal basin fragments (Neoproterozoic) in the northeastern Saxothuringian Zone (Germany): Neues Jahrbuch Geologie Paläontolo-gie, Monatshefte, v. 2001, p. 321–342.

Buschmann, B., Elicki, O., and Jonas, P., 2006, The Cadomian unconformity in the Saxo-Thuringian Zone, Germany: Palaeogeographic affi nities of Ediacaran (terminal Neoproterozoic) and Cambrian strata: Precambrian Research, v. 147, no. 3–4, p. 387–403, doi: 10.1016/j.precamres.2006.01.023.

Siberia

BalticaAvalonia

dCa omiaOpening of the

Rheicocean

Laurentia

Iapetus ocean

Panthalassaocean

Equator

c. 480 Ma

AmazoniaA

SXB

e fr aW st A ic

I

Figure 18. Paleogeography in the Lower Ordovician during the open-ing of the Rheic Ocean at ca. 480 Ma. A—Armorican Massif and French Massif Central; B—Teplá-Barrandian unit (Bohemian Massif); I—Iberia; SX—Saxo-Thuringian zone (Bohemian Massif). Modifi ed after C.R. Scotese (paleomap web site: www.scotese.com).


spe423-03 page 95

Christiansen, R.L., and Lipman, P.W., 1972, Cenozoic volcanism and plate-tec-tonic evolution of the western United States: Part 2, Late Cenozoic: Royal Society of London Philosophical Transactions, ser. A, v. 271, p. 249–284.

Condie, K.C., 1989, Plate tectonics and crustal evolution: Oxford, Pergamon Press, 492 p.

Coward, M.P., 1986, Heterogeneous stretching, simple shear and basin devel-opment: Earth and Planetary Science Letters, v. 80, p. 325–336, doi: 10.1016/0012-821X(86)90114-7.

Dickinson, W.R., 1981, Plate tectonics and the continental margin of California, in Ernst, W. G., ed., The geotectonic development of California: Engle-wood Cliffs, New Jersey, Prentice-Hall, p. 1–28.

D’Lemos, R.S., Iglis, J.D., and Samson, S.D., 2006, A newly discovered orogenic event in Morocco: Neoproterozoic ages for supposed Eburnean basement of the Bou Azzer inlier, Anti-Atlas Mountains: Precambrian Research, v. 147, no. 1–2, p. 65–78, doi: 10.1016/j.precamres.2006.02.003.

Drost, K., Linnemann, U., McNaughton, N., Fatka, O., Kraft, P., Gehmlich, M., Tonk, C., and Marek, J., 2004, New data on the Neoproterozoic-Cambrian geotectonic setting of the Teplá-Barrandian volcano-sedimentary suc-cessions: Geochemistry, U-Pb zircon ages, and provenance (Bohemian Massif, Czech Republic): International Journal of Earth Sciences, v. 93, p. 742–757, doi: 10.1007/s00531-004-0416-5.

Dufrenoy, P.A., 1838, Mémoire sur l’áge et la composition des terrains de tran-sition de l’Ouest de la France: Annales des Mines, v. 3, p. 91–100.

Elicki, O., 1997, Biostratigraphic data of the German Cambrian—present state of knowledge: Freiberger Forschungshefte, v. C 466, p. 155–165.

Fernández-Suárez, J., Gutiérrez-Alonso, G., and Jeffries, T.E., 2002, The importance of along-margin terrane transport in northern Gondwana: Insights from detrital zircon parentage in Neoproterozoic rocks from Ibe-ria and Brittany: Earth and Planetary Science Letters, v. 204, p. 75–88, doi: 10.1016/S0012-821X(02)00963-9.

Finger, F., Hanzl, P., Pin, C., von Quadt, A., and Steyrer, H.P., 2000, The Bru-novistulian: Avalonian Precambrian sequence at the eastern end of the central European Variscides, in Franke, W., Haak, U., Oncken, O., and Tanner, D., eds., Orogenic processes: Quantifi cation and modelling in the Variscan belt: London, Geological Society of London, Special Publica-tion 179, p. 103–112.

Friedl, G., Finger, F., McNaughton, N.J., and Fletcher, I.R., 2000, Deducing the ancestry of terranes: SHRIMP evidence for South America-derived Gond-wana fragments in central Europe: Geology, v. 28, p. 1035–1038.

Friedl, G., Finger, F., Paquette, J.L., von Quadt, A., McNaughton, N.J., and Fletcher, I.R., 2004, Pre-Variscan geological events in the Austrian part of the Bohemian Massif deduced from U-Pb zircon ages: International Journal of Earth Sciences, v. 93, p. 802–823.

Gaertner, von, H.R., 1944, Die Schichtgliederung der Phyllitgebiete in Thürin-gen und Nordbayern und ihre Einordnung in das stratigraphische Schema: Jahrbuch der Reichsanstalt für Bodenforschung, v. 62, p. 54–80.

Gebauer, D., and Friedl, G., 1994, A 1.38 Ga protolith age for the Dobra orthog-neiss (Moldanubian zone of the Southern Bohemian Massif, NE-Austria): Evidence from ion-microprobe (SHRIMP) dating of zircon: Journal of the Czech Geological Society, v. 39, no. 1, p. 34–35.

Gebauer, D., Williams, I.S., Compston, W., and Grünenfelder, M., 1989, The development of the central European continental crust since the Early Archaean based on conventional and ion-microprobe dating of up to 3.84 b.y. old detrital zircons: Tectonophysics, v. 157, p. 81–96, doi: 10.1016/0040-1951(89)90342-9.

Gehmlich, M., 2003, Die Cadomiden und Varisziden des Saxothuringischen Terranes—Geochronologie magmatischer Ereignisse: Freiberger For-schungshefte, v. C 500, p. 1–129.

Gerdes, A., and Zeh, A., 2006, Combined U-Pb and Hf isotope LA-(MC-)ICP-MS analyses of detrital zircons: Comparison with SHRIMP and new constraints for the provenance and age of an Armorican metasediment in central Germany: Earth and Planetary Science Letters, v. 249, no. 1–2, p. 47–62, doi: 10.1016/j.epsl.2006.06.039.

Glasmacher, U., Bauer, W., Clauer, N., and Puchkov, V.N., 2004, Neoprotero-zoic metamorphism and deformation at the southeastern margin of the East European craton, Uralides, Russia: International Journal of Earth Sciences, v. 93, p. 921–944, doi: 10.1007/s00531-004-0426-3.

Gradstein, F., Ogg, J., and Smith, A., eds., 2004, A geologic time scale 2004: Cambridge, Cambridge University Press, 589 p.

Graindor, M.J., 1957, Le Briovérien dans le Nord-Est du Massif armoricain: Mémoires pour servir a l’explication de la carte géologique détaillée de la France: Paris, Imprimerie Nationale, 211 p.

Hammer, J., 1996, Geochemie und Petrogenese der cadomischen und spätvariszi-schen Granitoide der Lausitz: Freiberger Forschungshefte, v. C 463, p. 1–107.

Hegner, E., and Kröner, A., 2000, Review of Nd isotopic data and xenocrys-tic and detrital zircon ages from the pre-Variscan basement in the east-ern Bohemian Massif: Speculations on palinspastic reconstructions, in Franke, W., Haak, U., Oncken, O. and Tanner, D., eds., Orogenic pro-cesses: Quantifi cation and modelling in the Variscan belt. Geological Society of London, Special Publication, v. 179, p. 113–129.

Heuse, T., Kroner, U., and Bartl, S., 2001, Tektono- und lithostratigraphische Kartierungskriterien für den Zentralteil des Schwarzburger Sattels: Geo-wissenschaftliche Mitteilungen von Thüringen, v. 9, p. 107–124.

Hoskin, P.W.O., and Schaltegger, U., 2003, The composition of zircon and igneous and metamorphic petrogenesis: Reviews in Mineralogy and Geo-chemistry, v. 53, p. 27–62, doi: 10.2113/0530027.

Janoušek, V., Gerdes, A., Vrána, S., Finger, F., Erban, V., Friedl, G., and Braith-waite, C.J.R., 2006, Low-pressure Granulites of the Liúov Massif, south-ern Bohemia: Viséan metamorphism of Late Devonian plutonic arc rocks: Journal of Petrology, v. 47, p. 705–744, doi: 10.1093/petrology/egi091.

Jolivet, L.M., Fournier, P., Huchnon, V.S., Rozhdestvenskiy, K.F.S., and Oscorbin, L.S., 1992, Cenozoic intracontinental dextral motion in the Okhotsk–Japan Sea region: Tectonics, v. 11, p. 968–977.

Kemnitz, H., Romer, R.L., and Oncken, O., 2002, Gondwana break-up and the northern margin of the Saxothuringian belt (Variscides of central Europe): International Journal of Earth Sciences, v. 91, p. 246–259, doi: 10.1007/s005310100209.

Keppie, J.D., Davies, D.W., and Krogh, T.E., 1998, U-Pb geochronological constraints on Precambian stratifi ed units in the Avalon composite terrane of Nova Scotia, Canada: Tectonic implications: Canadian Journal of Earth Sciences, v. 35, p. 222–236, doi: 10.1139/cjes-35-3-222.

Kerforne, F., 1901, Discordance du Cambrien sur le Precamrien, près de Rennes: Bulletin de la Société Géologique de France, v. 4, no. I, p. 2587–2590.

Kossmat, F., 1927, Gliederung des varistischen Gebirgsbaues: Abhandlungen des Sächsischen Geologischen Landesamtes, v. 1, p. 1–39.

Kríbek, B., Pouba, Z., Skocek, V., and Waldhausrová, J., 2000, Neoproterozoic of the Teplá-Barrandian unit as a part of the Cadomian orogenic belt: A review and correlation aspects: Vestnik Ceskeho geologického ústavu, v. 75, no. 3, p. 175–196.

Kroner, U., Linnemann, U., and Romer, R.L., 2003, Synthese der geologischen Geschichte des Saxothuringikums: Vom cadomischen Akkretionsorogen zum variszischen Kollisionsgebirge, in Linnemann, U., ed., Das Sax-othuringikum: Dresden/Bautzen, Staatliche Naturhistorische Sammlun-gen Dresden, p. 147–150.

Kroner, U., Hahn, T., Romer, R.L., and Linnemann, U., 2007 (this volume), The Variscan orogeny in the Saxo-Thuringian zone—Heterogenous overprint of Cadomian/Paleozoic Peri-Gondwana Crust, in Linnemann, U., Nance, R.D., Kraft, P., and Zulauf, G., eds., The evolution of the Rheic Ocean: From Avalonian-Cadomian active margin to Alleghenian-Variscan colli-sion: Boulder, Colorado, Geological Society of America Special Paper 423, doi: 10.1130/2007.2423(06).

Linnemann, U., 1991, Glazioeustatisch kontrollierte Sedimentationsprozesse im Oberen Proterozoikum der Elbezone (Weesensteiner Gruppe/Sachsen): Zentralblatt für Geologie und Paläontologie, v. 1, no. 12, p. 2907–2934.

Linnemann, U., 1996, Die Lagerungsverhältnisse und die sedimentäre Ent-wicklung des basalen Altpaläozoikums vom Langen Berg bei Gehren (Schwarzburger Antiklinorium, Saxothuringikum): Beiträge zur Geologie von Thüringen, v. 3, p. 73–84.

Linnemann, U., 2003a, The structural units of Saxo-Thuringia: Geologica Sax-onica, v. 48/49, p. 19–28.

Linnemann, U., 2003b, Sedimentation and geotectonic setting of the basin development of Saxo-Thuringia (Neoproterozoic–Lower Carboniferous): Geologica Saxonica, v. 48/49, p. 71–110.

Linnemann, U., 2007, Ediacaran rock complexes, the Cadomian orogeny and the problem of the Precambrian-Cambrian boundary in Germany (NE Bohemian Massif, central Europe): London, Geological Society of Lon-don Special Publication (in press).

Linnemann, U., and Buschmann, B., 1995a, Der Nachweis der cadomischen Diskordanz in einer Tiefenbohrung bei Gera und deren Bedeutung für das proterozoisch-paläozoische Standardprofi l im Schwarzburger Antiklino-rium: Geowissenschaftliche Mitteilungen von Thüringen, v. 3, p. 1–11.

Linnemann, U., and Buschmann, B., 1995b, Die cadomische Diskordanz im Saxothuringikum (oberkambrisch-tremadocische overlap-Sequenzen): Zeitschrift für Geologische Wissenschaften, v. 23, no. 5/6, p. 707–727.

Linnemann, U., and Heuse, T., 2000, The Ordovician of the Schwarzburg anti-cline: Geotectonic setting, biostratigraphy and sequence stratigraphy (Saxo-Thuringian Terrane, Germany): Zeitschrift der deutschen geologi-schen Gesellschaft, v. 151, p. 471–491.

96 Linneman et al.

spe423-03 page 96

Linnemann, U., and Romer, R.L., 2002, The Cadomian orogeny in Saxo-Thuringia, Germany: Geochemical and Nd-Sr-Pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance: Tectonophysics, v. 352, p. 33–64, doi: 10.1016/S0040-1951(02)00188-9.

Linnemann, U., and Schauer, M., 1999, Die Entstehung der Elbezone vor dem Hintergrund der cadomischen und variszischen Geschichte des Saxothu-ringischen Terranes—Konsequenzen aus einer abgedeckten geologischen Karte: Zeitschrift für Geologische Wissenschaften, v. 27, p. 529–561.

Linnemann, U., Gehmlich, M., Tichomirowa, M., Buschmann, B., Nasdala, L., Jonas, P., Lützner, H., and Bombach, K., 2000, From Cadomian subduc-tion to Early Paleozoic rifting: The evolution of Saxo-Thuringia at the margin of Gondwana in the light of single zircon geochronology and basin development (central European Variscides, Germany): London, Geologi-cal Society of London Special Publication 179, p. 131–153.

Linnemann, U., McNaughton, N.J., Romer, R.L., Gehmlich, M., Drost, K., and Tonk, C., 2004, West African provenance for Saxo-Thuringia (Bohemian Massif): Did Armorica ever leave pre-Pangean Gondwana? U/Pb-SHRIMP zircon evidence and the Nd-isotopic record: International Journal of Earth Sciences, v. 93, p. 683–705, doi: 10.1007/s00531-004-0413-8.

Ludwig, K.R., 2001, User’s manual for Isoplot/Ex rev. 2.49: Berkeley, Berkeley Geochronology Center Special Publication 1a, 56 p.

Massonne, H.-J., 1998, A new occurrence of microdiamonds in quartzofeld-spathic rocks of the Saxonian Erzgebirge, Germany, and their metamor-phic evolution: 7th International Kimberlite Conference, Cape Town, April 1998, extended abstracts, p. 552–554.

Mazur, S., Turniak, K., and Bröcker, M., 2004, Neoproterozoic and Cambro-Ordovician magmatism in the Variscan Klodzko Metamorphic complex (west Sudetes, Poland): New insights from U-Pb zircon dating: Interna-tional Journal of Earth Sciences, v. 93, p. 758–772.

McKerrow, W.S., Mac Niocaill, C., Ahlberg, P.E., Clayton, G., Cleal, C.J., and Eagar, R.M.C., 2000, The Late Palaeozoic relations between Gondwana and Laurussia, in Franke, W., Haak, U., Oncken, O., and Tanner, D., eds., Orogenic processes: Quantifi cation and modelling in the Variscan belt: London, Geological Society of London Special Publication 179, p. 9–20.

Murphy, J.B., and Nance, R.D., 1991, Supercontinent model for the contrasting character of Late Proterozoic orogenic belts: Geology, v. 19, p. 469–472, doi: 10.1130/0091-7613(1991)019<0469:SMFTCC>2.3.CO;2.

Murphy, J.B., Strachan, R.A., Nance, R.D., Parker, K.D., and Fowler, M.B., 2000, Proto-Avalonia: A 1.2–1.0 Ga tectonothermal event and con-straints for the evolution of Rodinia: Geology, v. 28, p. 1071–1074, doi: 10.1130/0091-7613(2000)028<1071:PAAGTE>2.3.CO;2.

Murphy, J.B., Pisarevsky, S.A., Nance, R.D., and Keppie, J.D., 2004, Neopro-terozoic–Early Paleozoic evolution of Peri-Gondwanan terranes: Implica-tions for Laurentia-Gondwana connections: International Journal of Earth Sciences, v. 93, p. 659–682.

Murphy, J.B., Gutiérrez Alonso, G., Nance, R.D., Fernández-Suárez, J., Kep-pie, J.D., Quesada, C., Strachan, R.A., and Dostal, J., 2006, Origin of the Rheic Ocean: Rifting along a Neoproterozoic suture? Geology, v. 34, p. 325–328, doi: 10.1130/G22068.1.

Nance, R.D., and Murphy, J.B., 1994, Contrasting basement isotopic signatures and the palinspastic restoration of peripheral orogens: Example from the Neoproterozoic Avalonian-Cadomian belt: Geology, v. 22, p. 617–620.

Nance, R.D., and Murphy, J.B., 1996, Basement isotopic signatures and Neo-proterozoic paleogeography of Avalonian-Cadomian and related terranes in the circum-North Atlantic, in Nance, R.D., and Thompson, M.D., eds., Avalonian and related peri-Gondwanan terranes of the circum-North Atlantic: Boulder, Colorado, Geological Society of America Special Paper 304, p. 333–346.

Nance, R. D., Murphy, J. B., and Keppie, J. D., 2002, A Cordilleran model for the evolution of Avalonia: Tectonophysics, v. 352, p. 1–21.

Oncken, O., 1997, Transformation of a magmatic arc and an orogenic root dur-ing oblique collision and its consequences for the evolution of the Euro-pean Variscides (mid-German crystalline rise): Geologische Rundschau, v. 86, no. 1, p. 2–20.

Roberts, D., and Siedlecka, A., 2002, Timanian orogenic deformation along the northeastern margin of Baltica, northwest Russia and northeast Norway, and Avalonian-Cadomian connections: Tectonophysics, v. 352, p. 169–184, doi: 10.1016/S0040-1951(02)00195-6.

Samson, S.D., D’Lemos, R.S., Blichert Toft, J., and Vervoort, J.D., 2003, U-Pb geochronology and Hf-Nd isotope compositions of the oldest Neopro-terozoic crust within the Cadomian orogen: New evidence for a unique juvenile terrane: Earth and Planetary Science Letters, v. 208, p. 165–180, doi: 10.1016/S0012-821X(03)00045-1.

Schneider Santos, J.O., Hartmann, L.A., Gaudette, H.E., Groves, D., McNaugh-ton, N.J., and Fletcher, I.R., 2000, A new understanding of the provinces of the Amazon craton based on integration of fi eld mapping and U-Pb and Sm-Nd geochronology: Gondwana Research, v. 3, p. 453–488, doi: 10.1016/S1342-937X(05)70755-3.

Sircombe, K.N., 2004, AgeDisplay: An Excel workbook to evaluate and dis-play univariate geochronological data using binned frequency histograms and probability density distributions: Computers & Geosciences, v. 30, p. 21–31.

Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead iso-tope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207–221, doi: 10.1016/0012-821X(75)90088-6.

Tait, J.A., Bachtadse, V., Franke, W., and Soffel, H.C., 1997, Geodynamic evo-lution of the European Variscan fold belt: Paleomagnetic and geological constraints: Geologische Rundschau, v. 86, p. 585–598, doi: 10.1007/s005310050165.

Tichomirowa, M., 2003, Die Gneise des Erzgebirges—hochmetamorphe Äqui-valente von neoproterozoisch-frühpaläozoischen Grauwacken und Grani-toiden der Cadomiden: Freiberger Forschungshefte, v. C 495, p. 1–222.

Unrug, R., 1996, Geodynamic map of Gondwana Supercontinent assembly: Orléans, France, Bureau de Recherches Géologiques et Minéres Orléans.

Van der Voo, R., 1979, Paleozoic assembly of Pangea: A new plate tectonic model for the Taconic, Caledonian and Hercynian orogenies: Eos (Trans-actions, American Geophysical Union), v. 60, p. 241.

Wendt, J.I., Kröner, A., Fiala, J., and Todt, W., 1993, Evidence from zircon dating for existence of approximately 2.1 Ga old crystalline basement in southern Bohemia, Czech Republic: Geologische Rundschau, v. 82., p. 42–50.

Wendt, J.I., Kröner, A., Fiala, J., and Todt, W., 1994, U-Pb zircon and Sm-Nd dating of Moldanubian HP/HT granulites from south Bohemia, Czech Republic: Journal of the Geological Society of London, v. 151, p. 83–90.

Wernicke, B., 1985, Uniform-sense normal simple shear of the continental lith-osphere: Canadian Journal of Earth Sciences, v. 22, p. 108–125.

Windley, B.F., 1995, The evolving continents (3rd edition): Chichester, Wiley, 526 p.

Wucher, K., 1967, Ergebnisse der Kartierungsbohrungen Heinersdorf 1/60 und 2/62 (Thüringisches Schiefergebirge): Jahrbuch für Geologie, v. 1, p. 297–323.

Zeh, A., and Wunderlich, J., 2003, Mitteldeutsche Kristallinzone, in Seidel, G., ed., Geologie von Thüringen: Stuttgart, E. Schweitzerbart’sche Verlags-buchhandlung, p. 24–51.

Zeh, A., Brätz, H., Millar, I.L., and Williams, I.S., 2001, A combined zircon SHRIMP and Sm-Nd isotope study of high-grade paragneisses from the mid-German crystalline rise: Evidence for northern Gondwanan and Grenvillian provenance: Journal of the Geological Society of London, v. 158, p. 983–994.

Zeh, A., Williams, I.S., Brätz, H., and Millar, I.L., 2003, Different age response of zircon and monazite during the tectono-metamorphic evolution of a high grade paragneiss from the Ruhla crystalline complex, central Ger-many: Contributions to Mineralogy and Petrology, v. 145, p. 691–706, doi: 10.1007/s00410-003-0462-1.

Zeh, A., Gerdes, A., Will, T.M., and Millar, I.L., 2005, Provenance and mag-matic-metamorphic evolution of a Variscan island-arc complex: Con-straints from U-Pb dating, petrology, and geospeedometry of the Kyff-häuser crystalline complex, central Germany: Journal of Petrology, v. 46, p. 1393–1420, doi: 10.1093/petrology/egi020.

Zulauf, G., Schitter, F., Riegler, G., Finger, F., Fiala, J., and Vejnar, Z., 1999, Age constraints on the Cadomian evolution of the Teplá Barrandian unit (Bohemian Massif) through electron microprobe dating of metamorphic monazite: Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, v. 150, no. 4, p. 627–639.

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