2.67 Ga H-P granulite metamorphism in the Tetons The earliest Himalayan-type

orogeny in North America

B. Ronald Frost, Carol D. Frost, Patrick Hughes, and Kevin R. Chamberlain Dept. Of Geology and Geophysics

University of Wyoming

Structural provinces of the Wyoming province

IdahoUtah

Wyoming

Montana

S. Dakota

Nebraska

1 100

KM

Colorado

LaramieMountains

Beartooth Mountains

BighornMountains.

BlackHills

Wind RiverRange

Teton Range

N. Dakot a

A’A

Owl Creek Mountains

2.55 Ga. deformation

no deformation since 2.83 Ga.

2.67 Ga. orogenic

belt

2.66 - 2.63 Ga. accretion

Proterozoic

accretion

Jac k son

L a ke

N

M ount M oran

approximatelocation of cross

section

Quaternary and T ertiary

M esozoic and Paleozoic

M ount Owen Q . M onzoni te

W ebb Canyon intrusive sui te

myloniti c gneiss

M oose B asin gneiss

undi fferentiated layered gneiss

km

0 5

High-pressure granulites (Moose Basin gneiss) are preserved as a enclave in the

northernmost Teton Range.

Mafic garnet granulite

foliated garnet

amphibolite

Metapelitic schistQ-Plag-Bio-Ky-Gar

Isotropic amphibolite

f1

f2

f2

Structural Relations in the Moose Basin gneiss

Garnet-bearing leucosome in partially melted mafic granulite

Kyanite and garnet in pelitic gneiss

Decompression textures in pelitic schist

Ky

Cord

St

Sil

500 600 700 800 900 10000

2

4

6

8

10

12

14

And

KySil

peakmetamorphism

f1 and f2

T°C

Zr in rutilethermometer

dehydration meltingof amphibolite

P-T conditions for the Moose Basin gneiss

GRAIL

Pelitic rocks

Mafic rocks

Peak P Ksp-Opx-Gar ? Gar-Cpx-Opx(?)

f1 Gar-bio-ky-Ksp(?)

Hb-Plag-Gar

f2 Gar-bio-Ky-St Hb-Plag-Gar

Decompression

Ky-St to St-Sil to Sil -

Cord

Metamorphic History

2

N

45°

F2

WebbCanyonintrusivesuite

MooseBasinGneiss

maficgneiss, locallygarnetgranuliteassemblagespreserved

pelitic gneiss, Ky-Kspassemblageslocally preserved,withKy lyingalongtheL2 lineation.

meta-dioritedike

1

3 3

30°

2

4

Sketch showing the Structural Relations between the Moose basin and Webb Canyon

gneisses

Structure Event AgeNo foliation Peak P-T ?Rootless isoclinal folds

f1 ?

N-E trending isoclinal folds

f2 2.67 Ga

Igneous intrusion (and extension ?)

Webb Canyon gneiss

2.67 Ga

Open NE trending synform

f3

Igneous intrusion

Mt. Owen Quartz Monzonite

2.55 Ga

Summary of structural events

Structural provinces of the Wyoming province

IdahoUtah

Wyoming

Montana

S. Dakota

Nebraska

1 100

KM

Colorado

LaramieMountains

Beartooth Mountains

BighornMountains.

BlackHills

Wind RiverRange

Teton Range

N. Dakot a

A’A

Owl Creek Mountains

2.55 Ga. deformation

no deformation since 2.83 Ga.

2.67 Ga. orogenic

belt

2.66 - 2.63 Ga. accretion

Proterozoic

accretion

T e to n R a n g e W i n d R i v e r R a n g e O w l C r e e k

M o u n t a i n s

I d a h o

B lo c k

W y o m i n g P r o v i n c e

A ’A

e m p l a c e m e n t o f t h e

R e n d e z v o u s g a b b r o

p o s s i b l e a c c r e t i o n a r y

p r i s m o r f o r e - a r c b a s i n

E d i r e c t e d t h r u s t i n g

o f M o o s e B a s i n

g n e i s s

f o rm a t i o n o f W e b b

C a n y o n g n e i s s b y

d e c o m p r e s s i o n m e l t i n gf o l d i n g a n d b o u d i n a g e

o f 2 6 8 0 G a d i k e s

m a i n s t a g e o f t h e

B r i d g e r b a t h o l i t h

u n d e f o rm e d 2 6 8 0

G a d i k e s

S W to W - d i r e c t e d

t h r u s t i n g o n M t . H e l e n

S t r u c t u r a l b e l t

Schematic cross section across the western Wyoming province at 2.67 -2.68 Ga

Age and pressure of some Precambrian HP granulite

terranes

Tetons

LimpopoSMZ

Lewisian

NapierComplex

LimpopoCZ

SnowbirdHangshan

Grenville

Qinling

1.0 2.0 3.0Age(Ga)

0

4

8

12

16

20

Typical P for Archean metamorphism

• Continental collisions clearly were occurring by 2.67 Ga.

• Continental collisions may have been operating before 2.67 Ga, but either have not been recognized or completely recrystallized to lower pressure conditions

Conclusions