Digital Atlas of Idaho - ISU...
Transcript of Digital Atlas of Idaho - ISU...
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Digital Atlas of Idahohttp://imnh.isu.edu/digitalatlas
Parts of Blaine, Custer, and Lemhi Counties
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Aerial view of Fall Creek in Pioneer Mountains core complex. Note glaciated topography cut Eocene granite. Detachement is about halfway into the view, where the gray soft slopes change to the rocky cliffs.
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Geologic map of the Wood River Valley and Smoky Mountains.
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Tertiary Eocene granodiorite of the Smoky Mountains.
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Upper part of Wood River. Rocks are Challis Volcanics.
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West face of Boulder Mountains. White rocks low down are Eocene granite. Darker rocks above that include Eocene dacite porphry intrusive rocks and overlying Challis volcanic rocks. Also present are wall rocks of Paleozoic sedimentary rocks as chocolate chips. In foreground are glacial deposits. Boulder Creek is the prominent creek. View from the mouth of Baker Creek.
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Cross section of Galena quad north of Ketchum, showing relations on west face of Boulder Mountains.
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View of Sawtooth Range from Stanley Ranger Station. Photo by: Jim Cash, IGS
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Historical Marker of Yankee Fork mines
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Main Salmon River near Yankee Fork.
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View of Pennal Gulch Tuff capped by Tuff of Challis Creek Outflow unit.
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Outcrop of volcanic ash. Photo by: Jim Cash, IGS
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View of dacitic / rhyodacitic lava flow
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Close-up of Challis volcanic rock
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View of Tuff of Ellis Cr. With mafic intrusion and K-rich lava flow-Proterozoic Sediments in foreground.
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View of Twin Peaks.
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View of Challis volcanics looking down Garden Cr. From Fluorspar Mine
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Outcrop of dacitic or rhyodicitic lava with weathered out clasts along Garden Cr. Rd.
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Outcrop of Pennal Gulch Tuff capped by Tuff of Challis Creek, talus of Challis Creek Tuff in foreground. Photo by Jim Cash, IGS
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Closeup of Tuff of Pennal Gulch
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Close-up of Challis volcanic rock showing texture.
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View of Castle Rock - Copper Basin
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Close-up of Challis volcanics along Big Lost River at Deep Creek.
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View of rhyolite domes south of Challis (looking 220 deg from Highway 93)
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Close-up of Tuff of Camas Cr-Black Mountain showing texture.
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Close-up of mafic rock along Lick Creek showing texture. Photo by: Jim Cash, IGS
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View of Challis volcanics from Cherry Creek Road looking 160o. Photo by: Jim Cash, IGS
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View of Sheep Mountain from Cherry Creek Road. Photo by: Jim Cash, IGS
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View of northern Twin Peak. Photo by: Jim Cash, Idaho Geological Survey
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View of southern Twin Peak. Photo by: Jim Cash, Idaho Geological Survey
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Belt 1650-17501470-1420, 1500-1600
1800-2000
100-80Atlanta Lobe
52-45Challis
150, 42-35,N. Nevada
Albion>2500,1800, 720, 550, 350,
32
17-14SRP
17-0 Ma12-10
10-8
1370
720-670480
1650-1750Belt + 70 via
Cretaceous ss
1100-1000, Grenville
via Neoprot-Pz
1100-1000, Grenville
via Neoprot-Pz
Teton>2500
0-2 Y’stone
2400
6-4BLT
1850, 350AntlerBelt
OrofinoTerrane
250160-13090-100
25 to 40Rift Basin
60 to 80Bitterroot Lobe
Over 6000 detrital zircon analyses
720-670
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05
1015202530
0 20 40 60 80 100 120 140Upper Big Lost River at Lost River Field Station (2PL02) n=39
Num
ber
Relative probability
05
10152025
0 20 40 60 80 100 120 140
Antelope Creek (15PL02) n=37
Num
ber
Relative probability
020406080
100
0 20 40 60 80 100 120 140Lower Big Lost River (9JG96, 2PL00, T6-66-1,T6-12-1) n=183
Num
ber
Relative probability
0
1
2
3
0 500 1000 1500 2000 2500 3000Upper Big Lost River at Lost River Field Station (2PL02) n=21
Num
ber
Relative probability
0
1
2
3
0 500 1000 1500 2000 2500 3000Antelope Creek (15PL02) n=16
Num
ber
Relative probability
0123456789
0 500 1000 1500 2000 2500 3000Lower Big Lost River (9JG96, 2PL00, T6-66-1, T6-12-1) n=50
Num
ber
Relative probability
A
B
C
Big Lost RiverSystem
“Ghost” Neoproterozoic Grains
Abundant Eocene GrainsNo Cretaceous Grains
1800-1900 Ma Grains, recycledThrough Miss. Copper Basin Group, Trans- Hudson derivation
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SHRIMP ages Late Neoproterozoic grains, Big Lost System , n=80
0
2
4
6
8
10
12
500 550 600 650 700 750 800
Age ±2? fraction ±2?580 11 0.06 0.06637 10 0.14 0.11 670 7 0.29 0.16 703 7 0.32 0.16 736 8 0.19 ---relative misfit = 0.517
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820
780
740
700
660
620
580
540
500
0.07
0.09
0.11
0.13
0.6 0.7 0.8 0.9 1.0 1.1 1.2207Pb/235U
206Pb238U
Intercepts at -23±81 & 692.3±5.2 [±6.9] Ma
MSWD = 1.01
data-point error ellipses are 68.3% conf.
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520
560
600
640
680
720
760
800
Mean = 691.4±5.2 [0.75%] 95% conf.Wtd by data-pt errs only, 0 of 16 rej.
MSWD = 0.88, probability = 0.58(error bars are 2σ)
box heights are 2σ
12KD06 Neoproterozoic orthogneiss
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0
5
10
15
20
25
30
0 500 1000 1500 2000 2500Age (Ma)
Num
ber
8PL02 Wildhorse Creek, Source of the 660 Ma Grains
Ghost Grains
658 +/- 7 Ma670+/- 8 Ma677+/- 9 Ma684+/- 8 Ma
0
2
4
6
8
10
12
35 40 45 50 55 60 65Age (Ma)
Num
ber
N=30
Age of IntrusiveRocks in Pioneercore
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2600
2200
1800
1400
1000
600
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14207Pb/235U
206Pb238U
Intercepts at 101 ± 15 & 2674.4 ± 9.1Ma
MSWD = 4.8
data-point error ellipses are 68.3% conf.
6PL05 Felsic gneissArchean plutonic rock withdiscordance (zirconalteration) at 101 Ma (Cretaceous)FIRST ARCHEANAGE IN PIONEERS!!!
Therefore, Archean crustextends north to Pioneers
Age of Zircons (magmatic) =2700 Ma
100 Mametamorphism and Pb loss from zircons
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6 PL 05 Archean gneiss
6.1 = 2566 +/ 15 Ma6.2 = 2439 +/- 83 Ma
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1800
1400
1000
600
200
0.0
0.1
0.2
0.3
0.4
0 2 4 6207Pb/235U
206Pb238U
data-point error ellipses are 68.3% conf.
Oldest zircons are 1800 MaSome rims are 1440 MaData are messyRock is likelyA Mesoproterozoic metasediment(with 1800 to 1440 Ma zircon rims,
4PL05 Calc silicate gneiss(from the mafic gneiss)
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20.1 is 1465 Ma
30.1 = 1625+/- 7 Ma
4PL05 Tiny zircon in a metamorphosed calc silicate?
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695 Ma pluton
47 Ma pluton
Metasediment (paragneiss)Belt Supergroup protolith
2550 Ma pluton(orthogneiss)
From Dover, 1983