Origins and Strength of the Proto-Kern Canyon Fault, Sierra

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Origins and Strength of the Proto-Kern Canyon Fault, Sierra Nevada Batholith, and implications for the strength of continental lithosphere along a long- lived transpressional fault

Elisabeth Nadin Greg Hirth Jason Saleeby Contents

1. Overview of central and southern Sierra Nevada (CA) shear zones 2. Depth and temperature profile of a long-lived shear zone (proto-Kern Canyon fault) 3. Fabrics of undeformed vs deformed plutonic and deformed metasedimentary rocks 4. Estimates of stress along the fault 5. Strain rate estimates 6. Implications for the strength of the lithosphere with depth

Discussion section: questions on shear zones that arose during this year’s Structural Geology & Tectonics Forum There are lots of preserved shear zones in the central and southern SNB

Intra-arc deformation recorded by 14 mapped discrete ductile and ductile- brittle shear zones that are preserved at plutonic levels

Well studied: timing, sense of motion, P/T conditions, rock fabrics

New/in progress: timing, deformation conditions, stress/strain estimates

Nadin et al., 2016 Shear zones follow age gradients

Located between older/colder (>100 Ma) and younger/hotter (<95 Ma) sections of the batholith

strong horizontal thermal gradients developed between longitudinal age zones of the batholith (Barton & Hanson, 1989) --> ideal for strain localization Shear zones young from west to east deformation style changes from north to south* Contractional Contractionalàdextral Dextral *or at least it seems south is different from central 105 span of documented motion span of possible 100 motion weak, domainal deformation 95

Age (Ma) Age 85

75 Sawmill Long LakeCourtright/WishonKaiser PeakQuartz MountainSing PeakMt. HofBenchman CanyonVirginiaCascade CanyonGem Lake LakeRosy Finchproto-KernKern Canyon Canyon- White Wolf

118 ° 30’ 118 ° W Igneous Quaternary alluvium depths (km) Tertiary volcanic body 30 Cretaceous intrusives Mesozoic pendant rocks 3 proto-Kern Canyon fault Proto-Kern Canyon ° sample 36 T ˚C location

Fault: 03H 725˚

03B1 opportunity to 03B2 465˚ examine a vertical 02F 475˚ 02I 02B 415˚ 480˚ profile of a shear 02H 450˚ 02A2 zone 475˚

° 30’ 11F T varies with depth,35 510˚ 11H from ~415 to ~530 ˚C 485˚

11A 520˚

10D N 510˚ 10F

° 530˚ 35

10 5 0 10 Km Chapman et al., 2012 Nadin et al., 2016 118.75 118.5 LEGEND Batholithic Intrusives Non-Batholithic Elements Cretaceous, nondifferentiated Cenozoic sediments and volcanics ca. 95 - 84 Ma* Pole plots are of quartz c axes, lower hemisphere Late Cretaceous Rand schist ca. 94 - 100 Ma* Pre-faulting pluton (102 Ma) Tehachapi complex, nondifferentiated ca. 96 - 100 Ma*

metasedimentary ca. 98 - 102 Ma* basement remnants Quartz axes = random ca. 102 - 105 Ma*

36 pre-Jurassic, 118.25 nondifferentiated T ~725 ˚C (TitaniQ) P ~3.5 kbar (~11 km) (Al-in-hbl) 03H

03E– 03A– 03G 03D

02C–E 02I– 02B 02O 02F–H 02A 35.75

lley rk Va Lake Isabella th Fo Sou n=119

35.5 Pre-faulting pluton (102 Ma) 11G 11F 11H 11C- 11E 11B Quartz axes = random Walker Basin Kelso Valley N T ~520 ˚C (TitaniQ)

Breckenridge Fault P ~4 kbar (~13 km) (Al-in-hbl)

11A

Edison Fault

10A– 10C

White Wolf Fault 2 0 2 4 Tehachapi 2 0 2 4 6 Cummings Valley Structural Symbols

fault strike-slip fault Reverse fault (Neogene - Quaternary) 10D– 4 cm So. Sierra detachment system 10F o (Late Cretaceous - Paleocene) Rand “thrust” (Late Cretaceous) n=131 Dominant attitude of high temperature deformation fabric o o o o (~ 90 , 85-60 , 59-30 , < 30 dips)

S-C lineations in ETSZ (PKCF) Late Cretaceous mylonites Cretaceous Late

Garlock fault

additional sources: Saleeby et al. (1987; 2005), Ross (1989), Wood (1998) 118.75 118.5 LEGEND Batholithic Intrusives Non-Batholithic Elements Cretaceous, nondifferentiated Cenozoic sediments and volcanics ca. 95 - 84 Ma* Late Cretaceous Rand schist ca. 94 - 100 Ma* Tehachapi complex, nondifferentiated ca. 96 - 100 Ma*

metasedimentary ca. 98 - 102 Ma* basement remnants ca. 102 - 105 Ma*

36 pre-Jurassic, 118.25 nondifferentiated

03H

03E– 03A– 03G 03D

02C–E 02I– 02B 02O 02F–H 02A 35.75 FOV ~0.5 cm

lley rk Va Lake Isabella th Fo 03-B, northern PKCF (ca. 86 Ma Gold Ledge Sou granite, ~12 km crystallization depth) EBSD: measured single grains of dynamically recrystallized quartz

10-E, southernmost PKCF (ca. 102 Ma Bear 35.5

11G 11F 11H Valley Springs, ~20 km depth) 11C- 11E 11B Walker Basin Kelso Valley N

Breckenridge Fault

11A

Edison Fault

10A– 10C

White Wolf Fault 2 0 2 4 Tehachapi 2 0 2 4 6 Cummings Valley Structural Symbols

fault strike-slip fault Reverse fault (Neogene - Quaternary) 10D– 10F So. Sierra detachment system Whole-section scan; FOV ~3 cm o (Late Cretaceous - Paleocene) Rand “thrust” (Late Cretaceous) Dominant attitude of high temperature deformation fabric o o o o (~ 90 , 85-60 , 59-30 , < 30 dips)

S-C lineations in ETSZ (PKCF) Late Cretaceous mylonites Cretaceous Late

Garlock fault

additional sources: Saleeby et al. (1987; 2005), Ross (1989), Wood (1998) 118.75 118.5 LEGEND Batholithic Intrusives Non-Batholithic Elements Cretaceous, nondifferentiated Cenozoic sediments and volcanics ca. 95 - 84 Ma* Sample Age (Ma) T (˚C) Depth (km) Regime Late Cretaceous Rand schist ca. 94 - 100 Ma* Tehachapi complex, nondifferentiated ca. 96 - 100 Ma*

metasedimentary ca. 98 - 102 Ma* 02A 89 725 xlization; 11 3 basement remnants ca. 102 - 105 Ma*

36 pre-Jurassic, 118.25 nondifferentiated 475 deformation 02B 94 480 11 2 03H 02F 104 475 12 1 03E– 03A– 03G 03D 02H 95 485 11 3

02C–E 02I– 02B 02O 02F–H 02A 35.75 02E Met. 2 02I Met. 415 2 lley rk Va Lake Isabella th Fo Sou 02J Met. none (Kilian & Heilbronner, 2017)

35.5 regime 2

11G 11F 11H 11C- 11E 11B Walker Basin Kelso Valley N

Breckenridge Fault

11A

Edison Fault

regime 2 10A– 10C

White Wolf Fault 2 0 2 4 regime 3 Tehachapi 2 0 2 4 6 Cummings Valley Structural Symbols

fault strike-slip fault Reverse fault (Neogene - Quaternary) 10D– So. Sierra detachment system 10F o (Late Cretaceous - Paleocene) Rand “thrust” (Late Cretaceous) Dominant attitude of high temperature deformation fabric o o o o (~ 90 , 85-60 , 59-30 , < 30 dips)

S-C lineations in ETSZ (PKCF) Late Cretaceous mylonites Cretaceous Late

Garlock fault

metasedimentary ca. 98 - 102 Ma* basement remnants ca. 102 - 105 Ma*

36 pre-Jurassic, 118.25 nondifferentiated Sample Age (Ma) T (˚C) Depth (km) Regime 03B 86 550 (2-feldspar)à 12 3 03H 450

03E– 03A– 03G 03D 03C Quartzite 1?

02C–E 02I– 02B 02O 02F–H 02A 03F Phyllite none 35.75 03G Quartzite none

lley rk Va Lake Isabella th Fo Sou 35.5

11G 11F 11H 11C- 11E 11B Walker Basin Kelso Valley N

Breckenridge Fault

11A

Edison Fault

10A– 10C

White Wolf Fault 2 0 2 4 Tehachapi 2 0 2 4 6 Cummings Valley Structural Symbols

fault strike-slip fault Reverse fault (Neogene - Quaternary) 10D– 10F So. Sierra detachment system o (Late Cretaceous - Paleocene) 03F, slide scan Rand “thrust” (Late Cretaceous) Dominant attitude of high temperature deformation fabric o o o o (~ 90 , 85-60 , 59-30 , < 30 dips)

S-C lineations in ETSZ (PKCF) Late Cretaceous mylonites Cretaceous Late

Garlock fault

additional sources: Saleeby et al. (1987; 2005), Ross (1989), Wood (1998) 118.75 118.5 LEGEND Batholithic Intrusives Non-Batholithic Elements Cretaceous, nondifferentiated Cenozoic sediments and volcanics ca. 95 - 84 Ma* Late Cretaceous Rand schist ca. 94 - 100 Ma* Sample Age (Ma) T (˚C) Depth (km) Regime Tehachapi complex, nondifferentiated ca. 96 - 100 Ma*

metasedimentary ca. 98 - 102 Ma* basement remnants ca. 102 - 105 Ma* 11F 103 510 15 3

36 pre-Jurassic, 118.25 nondifferentiated 11H vein 485 3 03H 10A ca. 115* 20 3 03E– 03A– 03G 03D 10D ca. 100 510 20 3 lo-strain?

02C–E 02I– 02B 02O 02F–H 02A 35.75 10F ca. 100 530 20 ?

lley rk Va Lake Isabella th Fo Sou 10-F 35.5

11G 11F 11H 11C- 11E 11B Walker Basin Kelso Valley N

Breckenridge Fault

11A

Edison Fault

10A– 10C

White Wolf Fault 10-D 2 0 2 4 Tehachapi 2 0 2 4 6 Cummings Valley Structural Symbols

fault strike-slip fault Reverse fault (Neogene - Quaternary) *the orthogneiss of Tweedy Creek is considered a metasedimentary 10D– So. Sierra detachment system 10F o (Late Cretaceous - Paleocene) Rand “thrust” (Late Cretaceous) Dominant attitude of high unit inside the 90 Ma part of the Domelands suite temperature deformation fabric o o o o (~ 90 , 85-60 , 59-30 , < 30 dips)

S-C lineations in ETSZ (PKCF) Late Cretaceous mylonites Cretaceous Late

Garlock fault

additional sources: Saleeby et al. (1987; 2005), Ross (1989), Wood (1998) 02B (northern fault section) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 %.'( *+.,( More ! = 10 ) (Stipp & Tullis, 2003) Sample 02B 02H 03B1 03B2 03G 11H Stress (Mpa) 62 62 78 85 78 108 11H (southern fault section) 60 50 40 30 20 # of Grains # of 10 0

0 10 20 30 40 50 60 70 80 90 100 110 Bin Size (um) Sample ! (Mpa) T est (˚C) Depth (km) Strain Rate Strain rate equation: 03B1 78 465 +/-22 12 ~10-12 03B2 85 465 +/-22 12 ~10-12 from Hirth et al., 2001 02B 62 479 +/-28 11 10-12–10-13 02H 62 486 +/-7 11 ~10-13 Governed by: deformation regime (dislocation creep); 02I 40 414 +/-4 ~10-14 differential stress (grain size); temperature; fugacity 11H 108 483 +/-41 15 10-11–10-12 (Probably cooled/exhumed during/before deformation)

Geothermal gradient = 45C/km assumed for magmatic arc

x xx x x x

Nevitt et al., 2017 PKCF samples CONCLUSIONS

1. Exhumed fault zones are excellent natural laboratories that need further study in order to constrain realistic rock strengths in deformation zones

2. The Proto-Kern Canyon fault was active during Sierra Nevada magmatic activity (95–85) Ma, as a transpressional structure. The fault is exhumed to depths from ~10–20 km, and overprints igneous and metamorphic rocks

3. Deformation is effectively halted along the western contact with older (>100 Ma) intrusives, and is spaced through the younger intrusives along the eastern edge. Deformation fabrics are most intense in the youngest and warmest intrusive rocks.

4. Estimated fault stresses range from ~40–110 MPa, which, coupled with temperature estimates from 400–500 ˚C, yield strain rates from ~10-14 (in older, reheated metamorphic rocks) to 10-11 MPa (in the deepest/warmest rocks). [This is consistent with other shear zone studies in the SNB, i.e., Nevitt et al., 2017]. Discussion Questions from January SGTF

Strength of shear zones • Can equilibrium mineral assemblages in shear zone rocks be used to reliably quantify water content at time of deformation and therefore be used as evidence for hydrolytic weakening?

• How can we quantitatively relate quartz microstructures found in experimentally deformed rocks to those found in naturally deformed rocks? (I.e., when relating naturally deformed rocks to experimentally deformed rocks, how can we be sure we're comparing apples to apples?)

• What mechanisms control shear zone width?

• Given a large-scale shear zone that narrows through time and space as strain localizes, what evidence would be required in order to quantify shear zone thickness (width) at a given time?