Download Integrating isotopic and geochemical tracers

Integrating isotopic and geochemical
tracers, petrology and geochronology
into EarthScope research
Examples from the
Wyoming Province
Carol Frost
Kevin Chamberlain
Ron Frost
Present-day crustal structure
Karlstrom et al., 2005
Synthesis of CD-ROM expt.
Challenge for EarthScope
• Identify processes that over Earth
history produce observed crustal
structure
• Tools include geology, petrology,
geochemistry, isotope tracers,
geochronology
• EarthScope’s strength: Integration of all
information
Example of the Wyoming Province
.
• >3.5 Ga history
• 15% Archean exposure
Geophysical Transects of the Wyoming Province
CB OTS
Wyoming Prov.
Proterozoic
106th profile
N. Dakot a
Depth (km)
Deep Probe
WR OC
Mont ana
20
?
7.0
60
1
100
Moho
Deep Probe
Idaho
Ut ah
~2.63 Ga
accretion
Archean
Wyoming
Colorado
200
Sarex
400
CO WY
600
800
1000
WY MT
41°
VE = 9:2
area of BBMD
affected by
ca. 2.6 Ga events
43°
45°
47°
1200
1400 km
USA CAN
tectonic lineaments
Precambrian terranes
Proterozoic extension
Laramide uplifts
~km/s
3.0
6.3
6.7-7.0
7.0-7.8
7.9-8.5 (3300 kg/m 3)
8.0-8.5 (3330 kg/m 3)
49°
CB OTS
Proterozoic
1.5
2.1
S. Dakot a
Nebraska
Km
7.0
8.1
8.2
7.5
80
100
Proterozoic
kg/m3
~2500
2700
2900
3050
3290
BH
LM
0
Depth (km)
Teton-Wind R.
Domain
BT
6.5
40
0
Beartooth-Bighorn
Magmatic Domain
1.5
2.1
0
GFTZ
VS
MHB
20
40
60
Moho
80
106th profile
3310
100
0
200
400
CO WY
41°
600
43°
800
WY MT
1000
1200 km
USA CAN
45°
47°
49°
adapted from Chamberlain et al., 2003, Snelson et al., 1998 and Gorman et al., 2002
Beartooth-Bighorn
Magmatic Domain
2.85 Ga Bighorn batholith
intrudes older gneisses
Beartooth-Bighorn Magmatic Domain
data-point error ellipses are 68.3% conf 
0.64
2952 ± 4 Ma
0.62
3040
0.60
3000
206
Pb
238
U
2960
0.58
2920
2880
0.56
2840
0.54
0.52
15
16
17
207
Pb/
18
235
U
3.00 ± 0.02 Ga
Core: 3.25 ± 0.01 Ga
200mm
50mm
19
Beartooth-Bighorn Magmatic Domain
.
10
cont. arcs
BBMD
5
depleted mantle
0
Nd
-5
-10
-15
3.2
C. Bighorn gneiss
S. Bighorn gneiss
Bighorn batholith
Washakie block
W. Owl Creek Mts.
E. Beartooth Mts.
Bridger batholith
Louis Lake batholith
3.1
3.0
2.9
2.8
Time, Ga
2.7
2.6
2.5
Beartooth-Bighorn Magmatic Domain
Beartooth-Bighorn Magmatic Domain
.
Deep Probe
Beartooth-Bighorn
Magmatic Domain
Teton-Wind R.
Domain
1
Mont ana
CB OTS
Wyoming Prov.
Proterozoic
100
S. Dakot a
Nebraska
Km
Idaho
Ut ah
~2.63 Ga
accretion
Archean
WR OC
0
BT
6.5
?
7.0
40
60
7.0
8.1
8.2
7.5
Moho
80
Deep Probe
100
Proterozoic
Wyoming
Colorado
20
GFTZ
VS
MHB
1.5
2.1
area of BBMD
affected by
ca. 2.6 Ga events
Depth (km)
106th profile
Geophysical Transects of the Wyoming Province
N. Dakot a
0
200
Sarex
400
CO WY
600
1000
WY MT
41°
VE = 9:2
800
43°
45°
47°
1200
1400 km
USA CAN
tectonic lineaments
Precambrian terranes
Proterozoic extension
Laramide uplifts
~km/s
3.0
6.3
6.7-7.0
7.0-7.8
7.9-8.5 (3300 kg/m 3)
8.0-8.5 (3330 kg/m 3)
49°
CB OTS
Proterozoic
kg/m3
~2500
2700
2900
3050
3290
BH
LM
0
20
40
60
Moho
80
106th profile
3310
100
0
200
400
CO WY
41°
Geophysical model suggests:
faster lower crust overlain by
slower upper crust
1.5
2.1
Depth (km)
Petrology, geochemistry,
isotopes, geochron. predict:
anhydrous mafic residue in
lower crust overlain by older
felsic crust
600
43°
800
WY MT
1000
1200 km
USA CAN
45°
47°
49°
adapted from Chamberlain et al., 2003, Snelson et al., 1998 and Gorman et al., 2002
~2.67 Ga active margin tectonics
Teton
Range
N
Isotopically
evolved
granulites
Jackson
Lake
Isotopically
juvenile
gray gneiss
Mount Moran
km
0
14
formation of Webb
Canyon gneiss by
decompression melting
Opx+ Sil
8
Owl Creek
Mountains
Wind River Range
SW to W - directed
thrusting on Mt. Helen
Structural belt
undeformed 2680
Ga dikes
folding and boudinage
of 2680 Ga dikes
Grn + Cord
6
Idaho
Block
Ky
Sil
And
Wyoming Province
2
0
E directed thrusting
of western layered
gneiss
GRAIL
10
4
Teton Range
peak
metamorphism
f1 and f2
12
5
dehydration melting
of amphibolite
500
600
700
800
T°C
900
1000
A
emplacement of the
Rendezvous gabbro
possble accretionary
prism
main stage of the
Bridger batholith
A’
2680-2670 Ma
E directed thrusting
of western layered
gneiss
Owl Creek
Mountains
Wind River Range
Teton Range
formation of Webb
Canyon gneiss by
decompression melting
SW to W - directed
thrusting on Mt. Helen
Structural belt
undeformed 2680
Ga dikes
folding and boudinage
of 2680 Ga dikes
Mount Helen Structural Belt
N. Central Wind River Mountains
3 kilometers
Idaho
Block
Wyoming Province
A
emplacement of the
Rendezvous gabbro
possble accretionary
prism
A’
main stage of the
Bridger batholith
2680-2670 Ma
Ge olo gic Ma p of The Pre c a m bria n
Ro c ks of t he Wind Rive r Ra nge
Late Archean Plutons, 2.55 Ga. Granites
South Pass Supracrustals, 2.64 Ga greywackes and
associated volcanic rocks
Louis Lake Batholith, 2.62 Ga batholith, locally
charnockitic
Bridger Batholith, 2.67 batholith, weakly
metamorphosed
Pinedale
Migmatitic gneiss, dot indicates occurrence
of sheared gneiss in migmatite
MHSB
Mt. Helen Structural Belt, dashed line
gives possible continuation
Washakie Terrane, 2.8 Ga or
older gneisses
Kilometers
0
25
~2.67 Ga large-scale structures
could be imaged geophysically
lozenges of mafic,
ultramafic, and pelitic
granulites in mylonitic
granitic gneiss
2.63 Ga active margin tectonics
Accretion, magmatism
& deformation: Tin Cup
N. Dakot a
Mont ana
Beartooth-Bighorn
Magmatic Domain
Teton-Wind R.
Domain
1
100
S. Dakot a
Nebraska
Km
Idaho
Ut ah
area of BBMD
affected by
ca. 2.6 Ga events
~2.63 Ga
accretion
Archean
Proterozoic
Wyoming
Colorado
Tin Cup shear zone, ~5 km wide
Meredith, 2005
2.63 Ga active
margin
tectonics
N. Dakot a
Mont ana
Beartooth-Bighorn
Magmatic Domain
Teton-Wind R.
Domain
1
area of BBMD
affected by
ca. 2.6 Ga events
100
S. Dakot a
Nebraska
Km
Idaho
Ut ah
~2.63 Ga
accretion
Archean
Proterozoic
Wyoming
Colorado
S
~2.63 Ga plutons
??
Sierra Madre Bradley
Peak
S. Pass
N
R. Hills
E. Rock, B. Gap
Medina, Owl C.
Wyoming P.
N
2.63 Ga accretion of terranes, magmatism
.
Deep Probe
Beartooth-Bighorn
Magmatic Domain
Teton-Wind R.
Domain
1
Mont ana
CB OTS
Wyoming Prov.
Proterozoic
100
S. Dakot a
Nebraska
Km
Idaho
Ut ah
~2.63 Ga
accretion
Archean
WR OC
0
BT
6.5
?
7.0
40
60
7.0
8.1
8.2
7.5
Moho
80
Deep Probe
100
Proterozoic
Wyoming
Colorado
20
GFTZ
VS
MHB
1.5
2.1
area of BBMD
affected by
ca. 2.6 Ga events
Depth (km)
106th profile
Geophysical Transects of the Wyoming Province
N. Dakot a
0
200
Sarex
400
CO WY
600
1000
WY MT
41°
VE = 9:2
800
43°
45°
47°
1200
1400 km
USA CAN
tectonic lineaments
Precambrian terranes
Proterozoic extension
Laramide uplifts
~km/s
3.0
6.3
6.7-7.0
7.0-7.8
7.9-8.5 (3300 kg/m 3)
8.0-8.5 (3330 kg/m 3)
49°
CB OTS
Proterozoic
kg/m3
~2500
2700
2900
3050
3290
BH
LM
0
Depth (km)
Zircon dates from lower
crustal xenoliths cluster at
~2.62-2.65 Ga (Farmer et al.
2005)
1.5
2.1
Area appears not to be
underlain by fast lower crust
20
40
60
Moho
80
106th profile
3310
100
0
200
400
CO WY
41°
600
43°
800
WY MT
1000
1200 km
USA CAN
45°
47°
49°
adapted from Chamberlain et al., 2003, Snelson et al., 1998 and Gorman et al., 2002
Fast crust never there? Or destroyed?
Proterozoic
events
• 2.0 Ga rifting (Cox et al., 2000)
• 1.86-1.74 Ga collision along
– Great Falls (Mueller et al.,
2005; 2002)
– Cheyenne belt (Karlstrom
and Houston, 1984;
Chamberlain, 1998)
• 1.47 Ga rifting, Belt basin
(Sears et al., 1998)
• 1.43 Ga A-type magmatism
1.43 Ga A-type
magmatism, SE WY
1.43 Ga A-type magmatism
3
w ithout pyroxenes
O2
2
1
0
w ith pyroxenes
calc-alkalic
volcanic rocks
Pikes Peak G ranite
Pikes Peak Syenite
gabbros
²
lo
g
f
-1
-2
-3
600
W olf R iver G ranite
Sherm an M onzonite
ferrodiorites
W olf R iver Syenite
D ifferentiation trend for tholeiitic m agm as
700
800
T °C
900
1000
Petrology, isotopes:
A-type granites
require tholeiitic sources
and leave mafic residues
Geophysically, a mafic
underplate may be imaged
Continued rifting causes melting of differentiated
portions of earlier tholeiitic intrusions
crust
melts derived from
evolved portions of
tholeiitic plutons
asthenosphere
1.43 Ga A-type magmatism
• Frost et al. (Geology, 2001) calculated 15% of SW
US crust should be A-type underplate
• Deep probe x-section 7.xx layer
CD-ROM working group, 2002
Karlstrom et al., 2002
Snake
• Laramide orogeny
(Erslev, 2005)
• Tertiary magmatism
(Absaroka (Feeley,
2003), Black Hills (Duke,
2005), Rattlesnake Hills
(Hoch & Frost, 1993)
• Basin & Range
extension
• Yellowstone hotspot
(Dueker &Yuan, 2005;
Frost & Frost, 1997)
River
Plain
ESRP
Paleozoic sediment s
SE
BV F
0
Depth (km)
Phanerozoic
events
NW
volcanic rocks
10
gabbroic sill
20
part ial melt
30
Moho
40
50
0
50
100
150
200
250
Dist ance ( km)
300
350
400
450
Peng and Humphries, 1998
Geophysical + geologic studies have been fruitful…
..and we have learned
much from COCORP
to Deep Probe.
We are poised to
develop integrated
experiments that will
allow us to relate
crustal structure to the
processes of
lithospheric evolution.
.
Gorman et al., 2002