IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 20-03 BOISE-MOSCOW IDAHOGEOLOGY.ORG PARKER AND PEARSON
BABY JOE GULCH THRUST DESCRIPTION OF MAP UNITS Mmg McGowan Creek Formation (Mississippian)—Black to dark-gray and light-gray GEOLOGIC MAP OF THE NORTHERN PART OF THE LEADORE QUADRANGLE, LEMHI COUNTY, IDAHO siltstone and claystone and gray- to tan-weathering silty lime mudstone and lime mudstone. Bedding ranges from mm-scale laminations to tabular, decime- Cambrian plutonic rock and Ordovician to Devonian sedimentary strata. We CORRELATION OF MAP UNITS on the Wentworth scale (Lane, 1947). Carbonate rocks are described using ter-scale beds. Recessive, slope-forming unit, distinguished by abundant chippy Lund’s (2018) in the southeastern part of the map area. The Baby Joe Gulch Stuart D. Parker and David M. Pearson Mass-Movement metric units, with imperial units listed in parentheses. Multiple lithologies within cement. Bottom and top are mostly siliciclastic, while middle contains more thrust is planar for most of its trace, from Jakes Canyon to Italian Gulch. Though Department of Geosciences, Idaho State University Deposits Alluvial Deposits a rock unit are listed in order of decreasing abundance. Intrusive rocks are carbonate, including a lavender-weathering lime wackestone bed of a few poorly exposed, our mapping constrains a dip to the south-southwest at 30-40˚, meters thickness. Sharp bottom contact. Gradational upper contact is placed with parallel foliation developed within the pluton. In and west of Thompson 2020 Holocene quartz (Q), alkali feldspar (A), and plagioclase (P) on a ternary diagram (Streckeis- Gulch, the Baby Joe Gulch thrust clearly cut the Thompson Gulch thrust and associated mylonite. These rocks in the immediate footwall of the Baby Joe Qls Qal QUATERNARY en, 1976). Volcanic rock compositions were not studied here in detail. Composi- Huh (1967), “Milligen(?) and Three Forks Formations” of Ruppel (1968), “Three tional names for small exposures of Cenozoic dikes are from Ruppel (1968). Forks” of Lucchitta (1966), and “Trident member of the Three Forks Formation”, Gulch thrust exhibit a foliation that dips more shallowly to the west-southwest Pleistocene CENOZOIC ? “Lower Sappington”, and “McGowan Creek Formation” of Grader and others than constrained for the Baby Joe Gulch thrust, which suggests the presence of Intrusive (2016). May correlate with transgressive systems tract above the “Trident a footwall ramp. East of Italian Gulch, the trace of the Baby Joe Gulch thrust
Rocks ALLUVIAL DEPOSITS curves to the northeast and then appears to be truncated by the Railroad
A measured at a full section in the head of Jakes Canyon, ~0.75 km (0.5 mi) north Canyon thrust. In several places, the Beaverhead pluton rocks in the hanging
113° 22' 30" A 20' BB 17' 30" 113° 15' Td TERTIARY
o Qal Alluvium (Holocene)—Sub-rounded to angular, unconsolidated cobble-gravel and wall of the Baby Joe Gulch thrust are structurally overlain by calcareous mylon-
o o of the map area. o
o 36 o o o o o 44° 45' o 44° 45'
o 25
25 ite. Sense of slip is unclear. Top-to-NW sense of slip was interpreted in the imme-
7 o Mylonitic Rocks Sedimentary Rocks 28 o Msp Mmc? o
Msp o 20 20
40 Mr Thickness varies considerably, but is usually from 1-3 m (3-10 ft) in mountain diate footwall on the western side of Jakes Canyon. Top-to-NE sense of slip was
o
# Mb o Dj Dark- to light-gray dolomitic mudstone, fossilif-
Ú ¹ ¹
o Southern Northern
Ú¹ Td o
o interpreted in the immediate footwall on the eastern side of Jakes Canyon. o canyons. Fill of Beaverhead Valley is likely substantially thicker. o
¹
Mmg? ¹ 38 o Qls ¹
27 Ú o Qal 45o erous wackestone, and minor tan-weathering quartz arenite. Tabular bedding
Mmc 32 16 1 Facies Facies
21 Ü
o
Ü Ü
o Ü
30 20 ¹ o È
o 6 45
33 25 ¹ ¹
¹ ranges in thickness from ~0.5 m to 3 m, occasionally with calcite vugs at the top. ¹ È
Dj? 32 m o
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o
o ¹ o
C o o ? ? ¹ o
40 o sc
sc 14 42 ¹ Recessive weathering slope former, with isolated resistant beds. Fetid odor on
È
24 È 25 m Ü19
o 30 ¹ MASS-MOVEMENT DEPOSITS RAILROAD CANYON THRUST 25
o o #
o 56
20 o o sc 15
oo o o
o o
Ü25 sc PENNSYLVANIAN freshly broken surfaces. Flat to wavy (algal?) laminations on mm-scale are
o 30 58 o
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o
o
20 ¹ o 24 20 ¹ o
¹ o o ¹ 38
30 o Mb Qls Landslide deposits (Holocene to Pleistocene?)—Poorly-sorted, unconsolidated common. Rare rip-up clasts, minor scour pits, and ooids. Distinctive, fossiliferous
76 o o 24 o o 29
o 50 o o
o10 Qls the southeastern part of the map area. This thrust dips moderately to the SE, and
Mr 30 sediments resulting from downhill movement. Mapped on the basis of sections exposed on the Baby Joe Gulch thrust hanging wall. Exposures outside
o 36
¹ o
o ¹
Mr Mb o 13
Qls ¹ Mr hummocky topography and the presence of a head scarp. Typically associated of the Baby Joe Gulch thrust hanging wall consist of a thinner section of almost ¹
o o
o sc
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# ¹ 74 21 o with the shaley Railroad Canyon Formation.
o15 o ¹
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o
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15 Ú 18 o ¹
# o stretching lineations in the mylonite are ~ E-W oriented, parallel to stretching
18 24 77 o the Baby Joe Gulch thrust hanging wall contain a lower unit of unfossiliferous
23 o Msp
15 9 Ü ¹
# o
Ü o 17 o ¹ 15
È 31
È 38
# 28 o 45 58 m MISSISSIPPIAN lineations in the mylonite beneath the Thompson Gulch thrust. The footwall Ü
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È 34 o o Ü o o
È ¹ ? o
o
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23 30 o m b CENOZOIC INTRUSIVE ROCKS
Ü
81 ¹ ¹ Ü
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34 o mylonite lies above the Beaverhead pluton, visible in rare outcrops in Italian
o
14 m ¹ ¹ 28 Ú 6 dolomitic wackestone containing bivalves, brachiopods, crinoids,
25 o
o ¹ m ? sc Mmc
o ¹ 20 o
Yqgh o ¹ 40 ¹ PALEOZOIC ¹ ¹ ¹ o m ¹ o
28 o o 38 o
o ¹
¹ Gulch, Baby Joe Gulch, and Jakes Canyon. The relationship between mylonites ¹
20 ¹ 5 ¹
31 ¹ (possibly including ) and distinct beds of large
¹ o stromatoporoidea actinostroma ¹ 35 Qal
¹ 18 ¹
15 9 Ü ¹
Ü Ü 26
¹ È Ü 25 22
9 25 of the Railroad Canyon thrust, the Thompson Gulch thrust, and the mylonites in
Dj? Msp 21 o (cm-scale width) cladopora overlain by smaller (mm-scale width) amphipora.
o ¹ È 31 27 ¹ o m
o ?
o o Mmg Td Diabase (Eocene?)—
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16 ¹ o
o o Ü ¹ 30 ¹ ¹ 32 ¹ 12 m 26 Ü
o ¹
o o
o ¹
18 ¹ o
Ü Mb o o Everywhere observed, the bottom contact is sharp and marked by a tan-weath- the hanging wall of the Radio Tower thrust is unclear. The initially low-angle,
Ü 20 o
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10 o 38 41 4
16 35 34 34¹ 7 5 ¹ o
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Mmg? o 30 ¹ Ü
58
Ü ¹
Ü ¹
Ü ¹ ering quartz arenite. The basal sandstone contains well-sorted, well-rounded ¹ 34
# Ü ¹ 40 ¹ ? r
14 o ? ¹
¹ 21 38 feldspar. Subhedral to euhedral crystals 1-2 mm long of hornblende. Poorly
¹ 37 ¹ Dj o
Ü 40 6 32 r Dj o ¹ ¹ Ü13
Ü Ú11 10 DEVONIAN o
¹
o attitudes from the mylonite. It also appears to be cut by the higher-angle,
55 ¹ Ü ¹ m
22o
25 26 4 ¹ ¹ 70 42
¹22 sc ¹ exposed. Typically in dikes 1-3 m thick (3-10 ft), less commonly 15-30 m thick
# C’
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Mmc? ¹ ¹ 39 ¹ 20 33
¹
¹ 8 ¹ Ú Ü12
Ü 50 ¹ Ü Ü ¹ Ü
4 unconformity basement-involved Baby Joe Gulch and Italian Gulch thrusts. A well-exposed
o Ü
Msp Mr ¹¹ 21 20 m 20 Ü Ú
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12 o (50-100 ft).
Ü Mb 13 32 40
¹
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# 1 o Ü 10 Dj
50 Ü ¹ Ü 20 ¹
Ü ¹ ÚÜ o
Ú 23 33 ¹ WNW-ESE trending hanging wall syncline is observable on the eastern side of
Ü 12 38 # ¹¹10 unconformable. Upper contact is not observed on the Baby Joe Gulch thrust Ü 12 ¹ ¹ Ú
18SP14 Ü12Ú 4 7
o Ü ¹ o Ü SOs 13 o ¹
¹ o Ü 47
25 11 47 Ü
o 44 ¹ o SILURIAN o Ü
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¹ Railroad Canyon, just below an unnamed thrust that carries Kinnikinic Quartzite
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¹ o o plate, but is sharp when observed elsewhere. Section exposed below the Baby
Ú È o87 24 o
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48 17 ¹ 18SP15 Ü 39 È
38 ¹ 28 o ¹
2 m ¹ 21 o o 50 70 o ¹
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44 15 s in its hanging wall. ¹
¹ s o STRONGLY TECTONIZED PALEOZOIC STRATA Joe Gulch thrust is ~50 m (165 ft) thick and is likely Famennian in age (Scholten
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87 ¹
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19 Ü44 Ü Ok
1 ¹ ܹ 40
o
25 ¹ 28 Ú o
Ü8 and Hait, 1962; Grader and others, 2016); ~150 m (490 ft) are exposed above the Ü o
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30 20 Ok
m Ü 75 Ü 20 ¹
o Ü20 o 40 ¹ È
# È 18 35 os o
Ú 41 o Ü o unconformity
1 ¹ s 60 7
Ü Ü Baby Joe Gulch thrust and is likely Frasnian to Famennian in age. o o
29 27 8Ü 15 ¹ 62 RADIO TOWER THRUST 55
o ¹
o ¹ 20
35 o o o o 24
o ORDOVICIAN È o 30 ¹
19 # È b Gray to tan, massive brecciated
Mr ¹ 13
o
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83 o o Thrust
# 14 30 ¹ o
16 o# o 8 Intrusive ¹
62 ¹
Ü o o
32 sc Ü
Ü Ü Ü o Ü o 36
58 Mr 36 ¹ 15 33 15 o
¹ 60 ¹ Rocks
¹ o
21 Metasedimentary
Msp o 34 Ü ¹ 40 Ú m Ü
52 19SP40 Ü o o 16 Gulch southwestern part of the map area. Here, the thrust dips steeply to the south,
Ü
55 Ü Ü o
34 Ú o 31
68 o 15Ü
Ú m 42¹ 38¹ oo Rocks SOs Saturday Mountain Formation (Lower Silurian to Middle Ordovi-
80 ¹
¹ ¹ ¹ Gulch. Occasionally crudely foliated subparallel to the thrust contact. Poorly
sc 3 ¹ 36 Oi placing a ramp of the Quartzite of Grizzly Hill overtop a ramp of Paleozoic
Thompson Qal 55
o
¹ ¹ o ¹
¹ 38 o
¹ 55
r CAMBRIAN cian)—Splotchy, light- to dark-gray dolo-wackestone and bleached gray ¹ m Ü ¹ 19SP24 Ü o ¹
60 6 r m 35 SOs
¹ m Italian
sc ¹
Ü Ú¹ Gulch 20 4 sorted, sub-angular calcitic clasts range in size from coarse sand to pebble and
22 o Oi o Ü
¹
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48 Ü ¹ o o ¹
o ¹ o
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20 Ü ¹ 19 51 ¹ o Ü
o 41 ¹ 22 40 o
o Ü Ü ¹ ¹ o
o 37 Ü ¹ Ü 20
o 4 45 Thrust Ü
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81 Ü ¹
o Ü 27 26 are matrix supported. Approximate thickness of about 10-20 m (30-65 ft) where
26 ¹
40 Ü Ú footwall on the western side of Jakes Canyon resemble jasperoid, and are
Radio Tower o Ü ¹ 58 20
¹ Ü o 26 Ü
o Ü 41 Ü
13 ¹ ¹ ¹ ¹ ¹
¹ o
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15 26 m o 49
¹ predominantly exposed near Railroad Canyon. Cyclical light to dark layering at
Ü o
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17 22 ¹ ¹ 34 33
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48 Ü Ú
Thrust 76 Ú Mb ¹ o 37 61 mapped as a discrete unit. Elsewhere, smaller occurrences of similar rocks are
¹ o ¹ 19
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Ü Ü ¹ #
Ü 54 5 40 meter-scale is visible from a distance. Distinct mottled texture with occasional
o 44 o
22 r 14 Yqgh MESO-
r Ü
Ü 4 Ü ¹ not of mappable size and are commonly associated with calcareous mylonite
¹ Ü
# ? ¹7 35 20 Ú o 42 ¹ ¹
o
o 12
¹ ¹ o o 32
18 ¹
Dj o
52 o13 Ü ¹ graded beds and laminations. Abundant fossils in the lower and middle portion,
o ¹ o
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o 19 20
o o ¹
50 ¹ 19
o ¹ 35 o ¹
29 24 ¹ 15 # o PROTEROZOIC
o o ¹
Italian o
o Ü Ü29 (Pzm). mylonites of the Thompson Gulch thrust can be followed to the NW. The two ¹
40 ¹ o Ü
Ü Ü 12 o Ok
o Ü #
6 o
22 Ü
o 12 Ü o
# o Ü Ü Ü
Yqgh 25 16 39 42 Ü 18 Ü including: horn coral, , , crinoids, and brachiopods. Bottom o o favosites halysites ¹
Ü o
51 ¹ o
16 sc 8 o
Ü 30 Gulch 20 ¹ 15 ¹ 25
Ü 5Ü o
Ü È o 31
o
È
o o 28
o 20 29
o
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30 o 19 10 12 25 29 28
o
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o o o 10 o o contact is sharp with the Kinnikinic Quartzite. Exposed only in the Baby Joe
o o o o
¹ o Thrust ¹ o #
33 7 # ¹ 10 42 12 o 17 o# ? o o o
Dj o
o m m o
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35 ¹ 38 21 26 oo È o
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21 ¹ 4 ¹ 17 m Gulch thrust hanging wall. Upper contact is below a thin bed of sandstone of the
o 19
¹ ? ¹
o Dj 30 Light- to dark-gray, calcare- o 64
5 ¹ Ú¹
# 14 Ü 32 #
m #
o
o 30 34 13 14 ? o
Ü o the geomtry and kinematics of this fault. In both localities, the Radio Tower Ü Ü
Ü Ü ¹ 78
o Ü 34 #
¹ Ü
29 Ü 28 o
¹ 12
o
Ü 7 o ¹ 18 # Ok #
¹ Dj o 25
o ¹ o SOs 22 14 30 ¹ ¹ 3 o Ú
33 ous mylonite with well-developed foliation and calcite stretching lineation (Fig. ¹ o o #
32 ¹ o m SOs
¹
o 36 8 19
50 ¹ Ü m
¹ 14 23
# Ü Ü Ü Ü o
¹ 22
o Ü Ü
20 25 49 # Ü Radio Tower thrust cuts footwall mylonites of the Thompson Gulch thrust at a low-angle.
Ü 25 8 Ü o Ü o
Ü 18SP06 o ¹ 8 ? Ü ? r 33 Ü Ü # Ü
¹ ¹ o o 4 Ü 48 ¹ # ¹
7 Ü o 25 28 21 ? o Ü
r Formation (Lucchitta, 1966; Ruppel, 1968; Ruppel and Lopez, 1988; Evans and 21 o
40¹ b 19 Dj o 47 # 23 Ü ¹ ¹ o 75 È
19SP15 m 28 Ü 22 ? o ¹ oÜ 5 m ¹ 36 ¹ 36 ¹ 22 26
¹ o ¹ ¹ 30 23 ¹ 24 È ¹
¹ #
30 ¹ Hanging wall rocks are folded about ~NE-SW and WNW-ESE trending folds. 12 ¹ Thrust
Ü # ¹ Ü ¹ 34 # 11 INTRODUCTION
1 m # ¹ ¹¹
38 # 21 ¹ ¹ 18 o
Dj ? Green, 2003; Lund, 2018). Approximate thickness of 90 m (295 ft), based on ¹ ¹ # 47 -
¹ o o
o 24 12 o
14 ¹ o
Ú ¹# ¹ ¹ # # 62 Ok ¹ 2 ¹
Ú 18SP05 ¹# o o
Ü Oi 18 ¹ 22 m o ¹ Ok
Ü Ú o ¹
o29
o 44 #b oo15 ?
2 # 60 # 19 19SP38 Ü45 m Oi tion ranges from entirely calcareous, to partly siliceous, with siliceous material exposures just west of Italian Gulch. A comparable thickness of ~160 m (525 ft)
Oi # # # 8 20 46
m o
¹ Ok
23 ¹
¹ # 46 Ü ¹ Ok Ü
¹ o 79 ¹ r
Ü ¹ Ü
Ü ¹ rÜ Oi is exposed near Leadore Hill, ~15 km (9 mi) south of the map area.
42 ¹ o
Oi 42 ¹ Ü
# Qls ¹ ¹ Ü o ¹
20
¹ SOs ¹ ¹ ¹ ¹ ¹ Dj ¹ # 14 28 21 ¹ m # ¹ 34 53 o
4 17 ¹ 25Ú UNNAMED NORMAL FAULTS
o results within the study area were published by Ruppel (1:62,500-scale; 1968), Ú
# ¹ 55
33 b Gulch 4 o and sheath folds (Fig. 2). Isoclinal and sheath fold axial surfaces are subparallel 41 19SP19 Ü 18 5 m Ü
m # 7 # Joe SOs Ü o 15 ¹
o
# o ¹ 68 ¹ #
o ¹ 22 37 ¹ 56 Ruppel and Lopez (1:200,000-scale; 1988), Ruppel (1:100,000-scale; 1998), Evans ¹ Ok SOs 43 17 SOs È Oi to the foliation; fold axes, where measurable, are generally parallel to the
o 10 o
64 26 Ü È r # ¹ o Oi Baby 36 #
¹ and Green (1:100,000-scale; 2003), and Lund (1:50,000-scale; 2018). These maps r ¹
¹ # 24 16 m stretching lineation and are interpreted to have formed concurrently with Ok Kinnikinic Quartzite (Middle Ordovician)—Vitreous white quartzite with grain o
m 30 ¹ Ok Railroad Ü o NW and dips both directions at a high angle. These structures generally exhibit
33 Thrust Ü
¹ 12 showed many low-angle thrusts primarily within Paleozoic rocks within the
Beaverhead Canyon 28 mylonitization (Fig. 3). Stretched crinoid ossicles observed on some foliation boundaries not visible. Unit contains meter-scale beds. Unit forms talus slopes Oi o
o displacements of less than 100 m, but are crucial for understanding the appar-
¹ 10 ¹
o o ¹ 20 o 20 -
o Thrust o ¹ o o planes display long axes parallel to the stretching lineation. Mylonite exposures
o o
Qal Fault Ü o ent changing structural positions of the older thrusts. The largest mapped o 12 32
58 20 o 20 head Mountains range front. Recent mapping (1:24,000-scale) of the adjacent
28 o are bounded by obvious brittle fault contacts in several locations, including
Oi 26 o
4 Ok results in brown spots that weather into prominent pock marks. Commonly normal fault of this set can be traced from Leadville at the range front to near
30 19 Bannock Pass quadrangle to the north by the Montana Bureau of Mines and o45 o
# Oi o Thompson Gulch, Railroad Canyon, and Jakes Canyon. In other locations, such
o brecciated with orange-weathering siliceous matrix. Rare crossbeds with biotur-
¹
¹ the Digmore Mine in the Bannock quadrangle ~2.5 km (1.5 mi) to the north of
60 o
9 o Geology and Idaho Geological Survey (Lonn and others, 2019) documented a ¹ Ü ¹ Ü as ridges bounding Baby Joe Gulch, mylonite is interspersed with limestone,
# oo SOs Ú bated tops including vertical burrows. Lower contact with the Beaverhead ¹ the map area. It is unclear whether the large, west-side-down normal fault in
¹ 31
# 30 sub-Devonian angular unconformity and a generally intact, southeast-dipping
113° 22' 30" 20 48 ¹ dolostone, and sandstone. Between Jake Canyon and Thompson Gulch, calcare- A’ ¹ pluton is inferred to be nonconformable (Link and others, 2017), but is not 18 Dj Cedar Gulch belongs to this set. These faults may be related to the development
¹
¹ oo section of sedimentary rocks ranging from Devonian to Pennsylvanian in age, 42' 30" 26 Ok Ok 42' 30" ous breccia (Pzb) structurally overlies ~ 1 m thick, black, lavender-weathering, exposed. Unit is exposed only in the Italian Gulch thrust hanging wall. Apparent
Oi 52 oo8 # # of the Miocene basin containing Renova and Six Mile Creek formations in
25 o
o12 which is underlain in angular unconformity by Mesoproterozoic to Cambrian(?) -
Qal Qal thickness of ~ 140 m (460 ft) based on exposure east of Railroad Canyon. Railroad Canyon of the Bannock Pass quadrangle (Fields and others, 1985). SOs 35 quartzite. This revised stratigraphic framework precludes the need for many of ¹ Ok ¹ ed to represent a major, low-angle thrust fault zone with a predominantly ¹
b ¹ SOs? 55 oo 32 oo the previously mapped low-angle thrusts within the Bannock Pass and northern eastward transport direction (Fig. 4). Protolith was assigned to the Middle 36
m Ok Leadore quadrangles. The opportunity to investigate the potential juxtaposition ¹ Canyon Formation by Lund (2018). Apparent thickness ranges from 40-80 m ¹ BEAVERHEAD FAULT SYSTEM Qal of bedding-parallel and high angle thrusts within the map area, coupled with (130-260 ft) based on good exposures in Thompson Gulch and Railroad Canyon. PALEOZOIC INTRUSIVE ROCKS
Ok 16 the newly documented intact stratigraphy hypothesized to project southward
25 Normal faults related to the modern range front cut the previously described set
o
o into the current map area, were the main motivations to revisit the northern Oi r Felsic alkaline intrusions (Ordovician to Cambrian)—Pink to red, alkali feldspar 20' r - Beaverhead SOs Ok Leadore quadrangle during our 1:24,000-scale mapping campaign. Our work PALEOZOIC STRATA syenite and granite, and minor greenish-black diorite and gabbro. Recessive 4 nent scarps are most obvious in the eastern part of the map area, where the was supplemented by attitudes from Ruppel (1968) in the northeastern portion weathering, forming brownish-red slopes. Medium- to coarse-grained and Fault sc trace of the Beaverhead fault changes from ~ESE-WNW to ~N-S.
of the map area and we adopt the thrust nomenclature of Lund (2018) where Snaky Canyon Formation (Pennsylvanian)—Gray to brownish-gray, limy and rarely foliated. Exposed in Baby Joe Gulch thrust hanging wall. Correlative with B’ dolomitic wackestone and packstone, chert-rich silty lime mudstone, and
sc appropriate. 500-485 Ma (U-Pb zircon; Lund and others, 2010) Beaverhead pluton of Scholten
yellowish-brown quartz arenite with calcitic cement. Lower part is sandy, with REFERENCES o and Ramspott (1968). Kinnikinic Quartzite overlies these intrusive rocks with an o abundant fossiliferous thick- to thin-bedded wackestones-packstones. Bivalves, Base Map Credit erosional contact as has been documented ~30 km (20 mi) to the southeast Allmenginer, R.W., Cardozo, N.C., and Fischer, D., 2013, Structural Geology 11 brachiopods, crinoids, corals, and bryozoans are common. Chert (including for our mapping of sedimentary rocks in the northern part of the map area. This (Link et al., 2017). nd Topogr wood-grain chert of DeCelles, 1983) is common, ranging from isolated nodules Algorithms: Vectors and Tensors (2 ed.): Cambridge, UK, Cambridge University USGS paper map, provisional edition 1991, compiled from aerial MN includes the lowermost Quartzite of Grizzly Hill, which is overlain in angular Qal SCALE 1:24,000 17' 30" to irregular beds of nodular chert. Tabular beds of alternating wackestone to Press, 289 p. photograph checked in 1988. CAMBRIAN TO MESOPROTEROZOIC STRATA Transverse Mercator projection. 1927 North American Datum. GN 1 0.5 0 1 Snaky Canyon Formation. In contrast to this “northern” stratigraphy, rocks near silty lime mudstone with chert are common on 10-50 cm scale, occasionally in Batt, L.S., Pope, M.C., Isaacson, P.E., Montañez, I.P., Abplanalp, J., Lukasik, J.J. and o MILE 1.64 oW 12.4 Simo, J.A., 2008, Upper Mississippian Antler foreland basin carbonate and Shaded relief from 10 m DEM. FEET Qal the range front north of Leadore in the hanging walls of the Italian Gulch and 1000 0 1000 2000 3000 4000 5000 6000 7000 consists of dolomitic wackestone with sparse chert or sand. Rare, rounded, Yqgh Quartzite of Grizzly Hill (Cambrian to Mesoproterozoic?)—Gray to green, siliciclastic rocks, east-central Idaho and southwestern Montana, USA: distin- Declination from NOAA National Geophysical Data Center. Railroad Canyon thrusts carry Ordovician/Cambrian Beaverhead pluton and nonconformably overlying Ordovician Kinnikinic Quartzite, Silurian to Ordovi- spherical algal laminations of several centimeters in diameter were found in guishing tectonic and eustatic controls on deposition, in Lukasik, J.A., and Simo, KILOMETER dolomitic wackestone of the upper section. Fresh surfaces are muddy gray to thickness changes apparent over 10s of meters. Recessive-weathering, primarily T., eds., Controls on Carbonate Platform and Reef Development: SEPM Special UTM Grid and 1 0.5 0 1 2020 Magnetic North sc heterogeneity in stratigraphy across the map area is interpreted to be the result dull in color. Weathered surfaces are earthy brown. The presence of sandstone Publications 89, p. 147-170. Declination at Center of Map Contour interval 40 feet of two “overlapping” unconformities within the map area: (1) an Ordovician distinguishes this unit from Mississippian limestones. Lower section may be crossbeds, mud chips, graded beds, and ripples. Fine-grained quartz sand with Burmester, R.F., Lonn, J.D., Lewis, R.S. and McFaddan, M.D., 2016, Stratigraphy of the unconformity generally exposed within the Lemhi Range in east-central Idaho, partly correlative with the Bloom member of Skipp and others (1979) and the visible grain boundaries and abundant mica. Sub-rounded to rounded, predom- Lemhi subbasin of the Belt Supergroup, in MacLean, J.S., and Sears, J.W., eds., which is overlain by Kinnikinic Quartzite; and (2) a Devonian unconformity Quadrant Formation of Lucchitta (1966). Upper section may be partly correlative inantly quartz grains supported by a muddy matrix. Bottom contact not Belt Basin: Window to Mesoproterozoic Earth: Geological Society of America GOAT SS BANNOCKA DEADMAN with the Juniper Gulch member of Skipp and others (1979) and the Park City observed. Upper unit consists of 20-30 m of vitreous medium- to coarse-grained P PASS generally exposed within southwestern Montana (Sloss, 1954; Grader and Special Paper 522, p. 121-137. MOUNTAIN Formation of Cressman and Swanson (1964) and Lucchitta (1966). Gradational white quartzite with massive beds on the meter scale. Lower contact of upper others, 2016). Cressman, E.R. and Swanson, R.W., 1964, Stratigraphy and petrology of the Permian lower contact with Bluebird Mountain Formation. Top contact not observed in unit is gradational. An upper bed of 1-3 m of quartzite pebble to boulder rocks of southwestern Montana, U.S.: Geological Survey Professional Paper Mappedarea mapped area. Local thickness is likely ~800 m (~2600 ft), based on measured conglomerate is observed in several locations (Fig. 5). Clasts are well rounded IDAHO In the northern part of the map area, our mapping results agree with the gener- 313-C, 303 p. WEST OF RESERVOIR sections in Hawley Creek, < 10 km (6 mi) to the southeast (Cressman and - North South CREEK LEADORE ally southeast-dipping stratigraphic section described in the Bannock Pass Qal Swanson, 1964), and near Morrison Lake, MT, ~ 20 km (12 mi) to the southeast DeCelles, P.G. and Gutschick, R.C., 1983, Mississippian wood-grained chert and its LEADORE quadrangle to the north. Farther south in the map, these rocks are structurally able near Radio Tower Hill in southwestern part of map area, but strongly A’ (Lucchitta, 1966). angular near Grizzly Hill ~ 4 km (2.5 mi) to the north, where the restored uncon- A TION overlain by strongly foliated carbonate mylonite with a prominent stretching C-C’ Thompson Gulch QUADRANGLE LOCATION Research, v. 53, no. 4, p. 1175-1191. 9000 9000 formity dips 20˚ to the northeast. Age is uncertain. Possible trace fossils and PURCELL lineation (Fig. 1); these tectonites are interpreted to represent a regional shear Mb Bluebird Mountain Formation (Mississippian to Pennsylvanian)—Tan quartz SE C Thrust SHEEPHORNPEAK SPRING GULCH foliation Radio Tower POWDERHORN burrows (Lonn and others, 2019) suggest a tentative correlation with Cambri- m zone with a thrust sense of displacement. This mylonite armors many of the arenite with 0.5 to 1 m thick tabular interbeds of limestone and dolostone. Near an/Neoproterozoic quartzites in southwestern Montana (Lonn and Lewis, 2012; textures, in Thrust Baby Joe Gulch ridges near the range front. This thrust has some similar characteristics as the fault zones the unit is poorly exposed and recessive. Tabular beds occasionally A schematic bedding ADJOINING QUADRANGLES McDonald and Yakovlev, 2019). Alternatively, may correlate to the Jahnke Lake American Association of Petroleum Geologists Memoir 1, p. 108-121. 8000 “Thompson Gulch thrust” described by Lund (2018), so we retain that name. Mr T Thrust 8000 Member of the Apple Creek Formation (Burmester and others, 2016). Apparent Farther south, these rocks are, in turn, truncated by a south-southwest-dipping including ~ 2 cm diameter horizontal and vertical burrows. Fossil assemblage Evans, K.V., and Green, G.N., 2003, Geologic map of the Salmon National Forest and Dj schematic bedding This Technical Report is a reproduction of a map submitted as thrust fault that Lund (2018) named the “Baby Joe Gulch thrust”. The exposed thickness exceeds ~250-300 m (820-985 ft) on Radio Tower hill. vicinity, east-central Idaho: U.S. Geological Survey Geologic Investigations Series Qal includes inarticulate orbiculoidea brachiopods, rugose corals, bryozoa, crinoids, Msp Beaverhead part of a PhD dissertation. Its content, format, and interpreta- hanging wall of the Baby Joe Gulch thrust of Lund (2018) contains Cambrian/Or- Map I-2765, scale 1:100,000. 7000 m b 7000 and articulate brachiopods. Irregular quartz, calcite, and minor dolomite tions may not conform to IGS standards. Fault 113° 15' dovician plutonic rocks and Ordovician to Silurian sedimentary rocks not cement results in pock-mark weathering and splotchy, nodular, or honeycomb Fields, R.W., Rasmussen, D.L., Tabrum, A.R. and Nichols, R., 1985, Cenozoic rocks of present in the Bannock Pass quadrangle. North-northwest-striking normal faults Field work conducted in 2018 and 2019. appearance. Fine to medium quartz sand grains are subrounded to rounded STRUCTURAL GEOLOGY the intermontane basins of western Montana and eastern Idaho: a summary, in
Elevation (feet) truncated all rock units and older faults within the map area; the main range Mmc with moderate sorting. Sharp lower contact with Railroad Canyon Formation. Flores, R.M., and Kaplan, S.S., eds., Cenozoic Paleogeography of the West-Central 6000 ? Qal 6000 Funding for this research was provided by NSF-Tectonics EAR-1728563. Elevation (feet) sc Oi front of the Beaverhead Mountains north of Leadore is bounded by the active ? Map version 11-24-2020. Gradational contact with overlying Snaky Canyon Formation was mapped - United States, Rocky Mountain Paleogeography Symposium 3: Rocky Mountain Ts? Beaverhead normal fault and represents the southern boundary of bedrock Mb where carbonate beds outnumber sandstone beds. Fossiliferous near the top. zoic sedimentary rocks that form a conformable, southeast-dipping panel. Section, Society for Sedimentary Geology, p. 9-36. Mmg foliation mapping conducted during the present study. Dj Correlative with the type Bluebird Mountain Formation in the southern Beaver- These rocks were folded by open to tight, 5-10 m wavelength, detachment-style Grader, G.W., Isaacson, P.E., Doughty, P.T., Pope, M.C. and Desantis, M.K., 2016, Idaho 5000 5000 head Mountains (Skipp and others, 1979) and the lowermost Quadrant Forma- folds that plunge gently to the southeast. These folds are best observed in the Lost River shelf to Montana craton: North American Late Devonian stratigraphy, tion of Lucchitta (1966). Poorly constrained thickness of ~60 m (195 ft), based on Msp, Mr, and Psc units, particularly in the northwestern and northern part of the surfaces, and intrashelf basin, in Playton, T.E., Weissenberger, J., and Kerans C., Yqgh SYMBOLS measured section ~ 20 km (12 mi) to the southeast, near Morrison Lake, MT schematic bedding map area. Fold asymmetry and kinematic indicators suggest top-to-the-north- New advances in Devonian Carbonates: Outcrop analogs, reservoirs, and 4000 4000 (Lucchitta, 1966). east displacement along bedding surfaces. Bedding and fold hinges were both chronostratigraphy: Society of Economic Paleontologists and Mineralogists similarly tilted toward the southeast prior to burial beneath a carbonate mylon- Special Publication 107, p. 347-379. A ite that characterizes the base of a later, structurally higher thrust system that Sense of slip (in cross section): A, away from observer; T, toward observer. Mr Railroad Canyon Formation (Mississippian)—Gray siltstone, black papery shale, Huh, O.K., 1967, The Mississippian system across the Wasatch line east central T we call the Thompson Gulch thrust. Beneath the Thompson Gulch thrust, the 3000 3000 orange- to gray- weathering banded lime mudstone and siltstone, with rare Idaho, extreme Southwestern Montana: Montana Geological Society 18th wackestone, packstone, and grainstone. Poorly exposed, except at the type sedimentary rocks locally exhibit a pervasive low-angle pressure solution Annual Field Conference, p. 31-62. Lithostratigraphic contact: dashed where approximately located; cleavage. This pressure solution cleavage accommodated up to ~50% sub-verti- dotted where concealed. section south of Hood Gulch, ~1.5 km (1 mi) north of the map area (Wardlaw Lane, E.W., 1947, Report of the subcommittee on sediment terminology: Transac- and Pecora, 1985; Ruppel and Lopez , 1988; Batt and others, 2008). Forms low-re- tions of the American Geophysical Union, v. 28, no. 6, p. 936-938. Tectonostratigraphic contact between mylonite and breccia: dashed where and is interpreted to have formed during footwall burial beneath the overlying approximately located. thrust system. Link, P.K., Todt, M.K., Pearson, D.M. and Thomas, R.C., 2017, 500–490 Ma detrital
North South Shows association with landslide deposits. Lower contact is sharp, marked by zircons in Upper Cambrian Worm Creek and correlative sandstones, Idaho, N
’ abundant, chippy shales and siltstones with mm-scale layering. Middle portion O
C Montana, and Wyoming: Magmatism and tectonism within the passive margin,
I Thrust fault: teeth on hanging wall; dashed where approximately located; - B’ B Grizzly T contains distinctly banded 10-30 cm tabular beds of massive gray-weathering In the central and southern parts of the map area, mylonite occurs at two
C Lithosphere, v. 9, no. 6, p. 910-926.
C dotted where concealed; arrow indicates dip; question mark where 9000 30 Hill E schematic bedding Thompson Gulch 9000 structural positions: above the relatively undeformed upper Paleozoic dip panel S poorly known; color coded with name labeled near type locality. Lonn, J.D., and Lewis, R.S., 2012, Geologic map of the Polaris 7.5’ quadrangle, south- Thrust Italian Gulch siltstone. Upper portion contains chert, carbonate grainstone with heterolithic and above the lower Paleozoic intrusive and sedimentary rocks in the hanging foliation Thrust Thompson Gulch thrust clasts, and shale. Upper contact with Bluebird Mountain Formation is sharp. walls of mapped thrusts near the range front. After mylonitization, mylonites in western Montana: Montana Bureau of Mines and Geology Open-File Report 621, sc m scale 1:24,000. 8000 A schematic bedding Railroad Canyon 8000 Correlative to “Big Snowy Formation basal siltstone and shale” and “upper Big both structural positions were folded about WNW-ESE and WSW-ENE trending m Railroad Canyon thrust Mb T Snowy/Railroad Canyon Formation” of Lonn and others (2019). Measured folds and truncated by several, generally south-dipping thrust faults (see Lonn, J.D., Elliott, C.G., Stewart, D.E., Mosolf, J.G., Burmester, R.F., Lewis, R.S., and Railroad Canyon Beaverhead Baby Joe Gulch thrust SOs thicknesses at the neighboring type section varies from 205 m (670 ft, Wardlaw Pearson, D.M., 2019, Geologic map of the Bannock Pass 7.5' quadrangle, Beaver- Mr schematic bedding Fault ) Thrust and Pecora, 1985), to 260 m (850 ft, Ruppel and Lopez, 1988), to 320 m (1050 ft, most notably in Jakes Canyon. head County, Montana, and Lemhi County, Idaho: Montana Bureau of Mines and t 7000 7000 Italian Gulch thrust e m
e foliation
f Qal Ok Batt, 2006). Variability in measured thicknesses is likely due to previously unrec- Geology Geologic Map 76, 1 sheet, scale 1:24,000.
(
n Radio Tower thrust
o ognized normal faults that occur in the vicinity of the type section (Lonn and i
t Lucchitta, B.K., 1966, Structure of the Hawley Creek area, Idaho-Montana: Pennsyl- a
E THOMPSON GULCH THRUST v l Normal fault: ball and bar on hanging wall; long dashes where others, 2019).
e
e ? Qal vania State University Ph.D. dissertation, 235 p. l
6000 Msp 6000 v E ? a
t approximately located; short dashes where location inferred;
i Oi Ts? o Lund, Karen, 2018, Geologic map of the central Beaverhead Mountains, Lemhi n dotted where concealed. Lund (2018) designated “greenschist-facies, isoclinally folded, marble phyllite” as
(
f e Msp Scott Peak Formation (Mississippian)—Dark- to light-gray weathering fossilifer- County, Idaho, and Beaverhead County, Montana: U.S. Geological Survey, e ? a “tectonite” in the hanging wall of the Thompson Gulch thrust. Our work builds
t
Mmg ) Anticline axial trace; dashed where approximately located; 5000 Mmc 5000 ous wackestone and packstone with lesser lime mudstone containing chert. dotted where concealed; question mark where existence questionable; a strong foliation and prominent stretching lineation (Fig. 1); we thus refer to plunge direction shown. steep canyon walls. Rare crossbedding in lenticular beds of encrinites with sharp 2010, SHRIMP U-Pb dating of recurrent Cryogenian and Late Cambrian-Early Dj ? 4000 Yqgh? 4000 Syncline axial trace; dashed where approximately located; top and bottom contacts. Uncommon beds of nodular, sometimes thrust sheet occur structurally above the Paleozoic dip panel in the northern Ordovician alkalic magmatism in central Idaho: Implications for Rodinian rift Yqgh dotted where concealed; question mark where existence questionable; wood-grained chert. Common fossils include crinoid stem fragments (up to 1 part of the map area and generally armor ridgelines in a continuous panel. The tectonics: Geological Society of America Bulletin, v. 122, p. 430-453. schematic bedding plunge direction shown. cm in diameter), brachiopods, bryozoa, and corals (including rugose and base of this mylonite cuts up section toward the east and dips gently to the Mamet, B.L., Skipp, B., Sando, W.J. and Mapel, W.J., 1971, Biostratigraphy of Upper lithostrotion). Gradational lower contact with the Middle Canyon Formation, 3000 3000 Overturned anticline axial trace; dashed where approximately located; southeast. The stretching lineation in the mylonite is well-developed, sub-hori- Mississippian and associated Carboniferous rocks in south-central Idaho: AAPG zontal, and roughly east-west trending (Fig. 3). Rare crinoid ossicles in the dotted where concealed; plunge shown. Bulletin, v. 55, no. 1, p. 20-33. upper contact with Railroad Canyon Formation, marked by shale overlying mylonite exhibit up to 30% stretching in a direction parallel to the stretching McDonald, C., and Yakovlev, P., 2019, Geologic map of the Twin Adams Mountain Overturned syncline axial trace; dashed where approximately located; thick-bedded tabular wackestone containing large (up to 15 cm long) caninid lineation. Syn-kinematic isoclinal and sheath fold hinges are loosely sub-parallel 7.5' quadrangle, southwestern Montana: Montana Bureau of Mines and Geology dotted where concealed; plunge shown. corals. Tabular, resistant beds often exhibit 1-5 m wavelength detachment-style to the east-west stretching lineation. Mylonites also occur in the southwestern Geologic Map 73, scale 1:24,000.
West East Monocline axial trace; dashed where approximately located; folds. Correlative to “Upper Madison Limestone” of Ruppel (1968), and “Mission part of the map area, where they are subparallel to and on top of basal Devonian
Canyon Formation” of Lucchitta (1966) and Huh (1967). Thickness of unit is strata that unconformably overlie the Quartzite of Grizzly Hill. The relationship Ruppel, E.T., 1968, Geologic map of the Leadore quadrangle, Lemhi County, Idaho: N
N arrow on steep limb.
’ ’
O Grizzly U.S. Geological Survey Geologic Quadrangle Map GQ-733, scale 1:62,500.
O o poorly constrained in map area. At least 400 m (1300 ft) is exposed in the north- A
I between this mylonite and the Thompson Gulch thrust is uncertain. Mylonites B
Thompson Gulch Thompson Gulch I
- -
C T C’ T
A Hill west part of the map area (comparable with 380 m (1245 ft) in the southern B
C Strike and dip of bedding. Ruppel, E.T. and Lopez, D.A., 1988, Regional geology and mineral deposits in and Thrust m Thrust C 30 9000 E 9000 sc E Thompson Gulch S m m r Beaverhead Mountains. The unit is twice as thick, 850 m (2790 ft) at the type WNW-ESE and NE-SW folds after mylonitization. Mylonites of the Thompson near the central part of the Lemhi Range, Lemhi County, Idaho: U.S. Geological
Mr Thompson S Salt Creek Strike and dip of bedding where sedimentary structures show bedding to Mb Thrust 30 locality in the southern Lemhi Range (Huh, 1967). Gulch thrust are also truncated by the Baby Joe Gulch and Radio Tower thrusts Survey Professional Paper 1480, 127 p.
Qls Railroad
Jakes Canyon Gulch Mr Mb be upright.
sc m Canyon at Thompson Gulch, and the Italian Gulch thrust on the western side of Italian Scholten, R. and Hait Jr, M.H., 1962, Devonian system from shelf edge to geosyn- 8000 Mb Thompson Gulch m 8000 oo Mr Strike of vertical bedding. Gulch. cline, southwestern Montana-central Idaho, Billings Geological Society:
Msp Mr Thrust s Mmc Middle Canyon Formation (Mississippian)—Dark-gray to black, silty lime Msp sc foliation Thirteenth Annual Field Conference: Three Forks - Belt Mountains Area and
m Strike and dip of overturned bedding. mudstone with bedded chert and sparse dolostone. Tabular beds range from Mr 30 ITALIAN GULCH THRUST Symposium: The Devonian System of Montana and Adjacent Areas, p. 13-22. ¹ ~5- 20 cm thick. Tan- to gray-weathering, recessive and slope-forming. Chert
) Mb
t 7000 Mmc 7000 Ü e Msp Qal Scholten, R. and Ramspott, L.D., 1968, Tectonic mechanisms Indicated by structural
e Msp 30 ranges from cm-scale layering, to 10-20 cm thick undulating, sometimes discon-
f 6 Strike and dip of foliation; arrow shows trend and plunge ( Mmc sc n Msp tinuous beds, to dm-scale isolated nodules. Uncommon silt to shale interbeds, framework of central Beaverhead Range, Idaho Montana: Geological Society of
o sc of stretching lineation.
Mr È
i t
E a particularly within ~ 20 m of the base of the section. Rare crinoid-bearing map area. This thrust dips moderately to the SSE and juxtaposed a hanging wall America Special Paper 104, 62 p.
l v Mmg Mb Mb
e e
v
l 6000 Dj 6000 30 Strike and dip of pressure solution cleavage.
a E Mmc of Beaverhead pluton, Kinnikinic Quartzite, Saturday Mountain Formation, Skipp, B., Hoggan, R.D., Schleicher, D.L. and Douglass, R.C., 1979, Upper Paleozoic Mmg Mmc t
Dj Mmg i Mr o Mmg Mr n carbonate bank in east-central Idaho; Snaky Canyon, Bluebird Mountain, and Ú
(
f Msp e Trend of minor fold hinge. map area (Lonn and others, 2019). Gradational upper contact is obscured, and its structurally overlying Thompson Gulch thrust mylonite. Notably, the
e
t 5000 5000 ) Kinnikinic Quartzite and Saturday Mountain Formation are not present beneath Survey Bulletin 1486, 88 p. Dj Mmg Dj Dj 19SP19 on the meter-scale. Contains 10s of meters of jasperoid (calcite replaced by the subjacent Thompson Gulch thrust’s footwall, which demonstrates substan- Yqgh Yqgh Msp Msp Sample locality of oriented thin section. Sloss, L.L., 1954, Lemhi arch, a mid-Paleozoic positive element in south-central Mmc silica) on the western side of Jakes Canyon. Correlative to “Lower Madison tial pre-thrusting stratigraphic complexities in the region. The Italian Gulch Idaho: Bulletin of the Geological Society of America, v. 65, no. 4, p. 365-368. schematic bedding schematic bedding # Limestone” of Ruppel (1968), “Lodgepole Formation” of Lucchitta (1966) and thrust is structurally overlain by the Railroad Canyon thrust and an isolated 4000 4000 # # Tectonic breccia outcrop. Streckeisen, A., 1976, To each plutonic rock its proper name. Earth-science reviews, Mmg Huh (1967), and “Middle Canyon Formation” of Huh (1967) and Mamet et al. Dj Mmg Dj v. 12, no. 1, p. 1-33. Yqgh Yqgh Yqgh Mmc (1971). Estimated thickness of ~ 200 m (560 ft) near the Digmore mine (Lonn southern range front near Railroad Canyon. The relationship between the Italian Mmc Mylonite outcrop. Yqgh Yqgh and others, 2019), is comparable with measured thicknesses of 250 m (820 ft) at Gulch and Baby Joe Gulch thrusts is unclear, as the two are apparently mutually Wardlaw, B.R., and Pecora, W.C., 1985, New Mississippian-Pennsylvanian 3000 3000 Lake Canyon, MT, ~15 km (9 mi) to the northeast (Huh, 1967), and 210 m (690 ft) crosscutting. Folds in the proximal hanging wall and footwall of the Italian stratigraphic units in southwest Montana and adjacent Idaho: U.S. Geological in the Hawley Mountains (Mamet and others, 1971). Gulch thrust are WSW-ENE trending. Survey Bulletin 1656-B, p. B1-B9.
N a 19SP38 b 19SP40
C 100 μm Mean vector of C 288 108 stretching lineation: 93.9 ± 2.8˚ c 19SP38 C’ C’
285° 1 cm 105° ~10 cm
Figure 4. Observed shear fabrics from mylonite of Thompson Gulch thrust at map localities shown in upper right stretching lineation N=274 corner of photos. Orientation (azimuth) shown in lower corners. a) Outcrop photo showing interpreted C-C’ fabrics. 100 μm - b) Photomicrograph (cross polarized light) showing mantled, σ-type porphyroclast with curving calcite twins. c) 280 100 tion ~1 meter above unconformity with underlying Quartzite of Grizzly Hill. pole to foliation N=435 Photomicrograph (cross polarized light) of mantled, δ-type porphyro right (ESE) sense of shear. mylonite fold hinge N=89
Figure 1. Carbonate mylonite with well-developed foliation and stretching lineation. Figure 2. Outcrop-scale similar folds in carbonate mylonite. White to tan layers are siliceous. Gray layers are calcareous. View is roughly Figure 3. Lower hemisphere stereographic projection (Allmendinger and others, 2013) of measured fabrics within toward east, approximately parallel to trend of fold hinges. carbonate mylonite. Kamb contours at 2σ intervals. Arrow shows mean vector of stretching lineation trends (red contours). Large blue circle denotes mean vector of poles to foliation measurements (blue contours). Radius of mean vector shows 2σ uncertainty of ± 3.2˚.
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