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
Jan 13, 2016
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