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HvE - Sedimentpetrologie

What are heavy minerals?

• fine to medium-grained sandstones, as fresh as possible (!)• crushing and desaggregation (e.g., 10% acetic acid, ultrasonic, H2O2, etc.• sieve fraction 63 – 125 µm (may be coarser, if necessary)• separation of HM by specific density fluids such as Na-metatungstate• counting of at least 200 grains under the microscope; embedded in special

resins or waxes with well defined optical properties (e.g., Meltmount 1.66) • for details see Mange & Maurer (1991, 1992)

→ amphibole, pyroxene, zircon, tourmaline, rutile, apatite, ...

→ are smaller than the average grain size of the sediment

→ accessory minerals in clastic sediments with a proportionof usually <1%

Heavy mineral analysis

→ minerals with a specific density ρ > 2.85 g/cm3

How to analyse them?

HvE - Sedimentpetrologie

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HvE - SedimentpetrologieBoenigk 1983

HvE - Sedimentpetrologie

Boenigk 1983

→ 63 – 125 µm

Grain-size dependence of HM assemblages

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HvE - Sedimentpetrologie

XYi = mineral X – mineral Y index= 100 * X / (X + Y)

ATi = Apatite – Tourmaline index= 100 * apatite / (apatite + tourmaline)

Morton & Hallsworth 1994

Hydraulicbehavior

HvE - Sedimentpetrologie

source area

sedimentary basin

Morton & Hallsworth 1994

weathering

abrasionmixing

sorting

authigenesis,intrastratal solution

Modification of HM assemblages

weathering

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HvE - SedimentpetrologieMorton & Hallsworth 1999

Occurrence and stability of HM (weathering profiles)

-decreasing stability -

HvE - Sedimentpetrologie Mange & Maurer 1991

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HvE - Sedimentpetrologie

Morton & Hallsworth 1999

instrastratalsolution

Modification of HM assemblages

HvE - Sedimentpetrologie

Tha-2

Sal-2

Huy-1

Foto

s: H

vE

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HvE - Sedimentpetrologie

SMA / NMA

CMM

Weathering on transit(alluvial storage)

example by Morton & Johnsson 1993

HvE - Sedimentpetrologie

SMA

NMA

CMM

CM/MA Llanosprox. mid. dist.

Morton & Johnsson 1993

Weatheringon transit

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HvE - Sedimentpetrologie

Example:

Lower RhineBay, Cologne

HvE - Sedimentpetrologie Boe

nigk

198

3

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HvE - Sedimentpetrologie Berger et al. 2005

HvE - Sedimentpetrologie

Schwerminerale

→ Minerale mit spezifischer Dichte ρ > 2.89 (2,86) g/cm3

(engl.: heavy minerals oder dense minerals)

→ Charakteristische Merkmale:

- Habitus (Form, Spaltbarkeit, Oberflächenstruktur, ...)- Farbe (Pleochroismus!)- Lichtbrechung (unterschiedl. Einbettungsmittel!)- Doppelbrechung (Mineraldicke und -orientierung beachten!)- Auslöschung, opt. Charakter/Interferenzbild, Einschlüsse, ...

→ für die spezifische Merkmale der einzelnen Minerale siehe v.a. Mange & Maurer 1991; im Skript sind nur einige Folien enthalten mit Bezug zur Schwermineralchemie

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HvE - Sedimentpetrologie

zircon

a: Eocene tuff horizonb: Carboniferous sediments

Meltmount 1,662100 µm

Mange & Maurer 1991

tetragonal, ρ = 4.60 – 4.79n = 1.92 – 2.02Δ = 0.042 – 0.065

HvE - Sedimentpetrologie

tourmaline

Meltmount 1,582

trigonal, 1- , ρ = 3.00 – 3.25, n = 1.61 – 1.66, Δ = 0.017 – 0.036

100 µm

EY 6-1 (LOS)H 1021-5 (BRA)

EY 9-34 (BRA)

EY 6-3/b (LOS)

EY 6-3/c (LOS)

EY 6-3/d (LOS)

detritaltourmaline grains

tourmaline frommetasandstoneclasts

Al(tot)

Al50Fe(tot)50 Al50Mg50

Elbaite

Schorl Dravite

Uvite

1

2

3

4

5

6

7

8

Henry & Guidotti 1985,von Eynatten & Gaupp 1999

elbaite

draviteschorl

1,2: granitoid host (source) rocks4,5,6: metasedimentary host (source) rocks

Henry & Guidotti 1985,von Eynatten & Gaupp 1999

uvite

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HvE - Sedimentpetrologie

rutile – properties and occurrence

• beside sphene and ilmenitethe most important Ti - mineralin the earth‘s crust

• stable in sedimentaryenvironments

• main primary occurrencein medium to high-grade metamorphic rocks

• chemistry:

TiO2 ( >99 wt.-%)

→ frequent occurrence as heavy mineral in (mature) clastic sediments

→ used for maturity (ZTR) and other indices reflecting source materials (RZi)

but ... Nb → 28000 ppmCr → 4400 ppmFe → >30000 ppmZr → 8400 ppm V → 7600 ppmW → 8100 ppmU → 84 ppm

tetragonal, 1 +n = 2.61 – 2.90Δ = 0.286 – 0.296

Man

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HvE - Sedimentpetrologie

0

1000

2000

3000

4000

5000

0 500 1000 1500 2000

Nb in ppm (rutile)

Cr i

n pp

m (r

utile

)

rutile frommafic rocks

rutile frommetapelitic rocks

metacumulates

2500 3000

28000

Zack et al. 2002, Chem Geol 184

Zack et al. 2004, CMP 184

rutile

11

HvE - Sedimentpetrologie0 0.05 0.15

2.0

1.5

1.0

0.5

0

MORB

IPB

IAB

TiO wt.-%2

Fe3+/(Cr+Al+Fe )3+

Cr/(

Cr+

Al)

Dick & Bullen1984

Pober & Faupl1988

Mg/(Mg+Fe )2+

01.0

A chromitites

cumulates(dunites)

harz-burgites

lherzolites

0.0

0.2

0.4

0.6

0.8

1.001.0

type-Iophiolites

type-IIIophiolites

type-IIophiolites

Bchromespinel

Diagramm nach Arai 1992,Daten aus v. Eynatten 1996

Meltmount 1,662

Kubisch ρ = 5.09n = 2.00Δ = ./.

HvE - Sedimentpetrologie

amphibole - ?

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HvE - Sedimentpetrologie

Mg-riebeckite

0.0

0.2

0.4

0.6

0.8

1.0

Fe2+

/(Mg+

Fe2+

+Mn)

Fe3+/(AlVI+Fe3++Ti)0.0 0.2 0.4 0.6 0.8 1.0

blue sodic amphiboles

von Eynatten et al.1999, Sed. Geol.

HvE - Sedimentpetrologie

(G) Case Studies

2. Schweizer Molassebecken (Zentralalpen-Vorland)

1. Oligo-/Miozänes Vorland der Betischen Kordillere

3. Subherzynes Kreidebecken (Harz-Vorland)

4. ... ... ...