Pliocene Sinistral Slip Across the Adobe Hills, Eastern California–Western Nevada: Kinematics of Fault Slip Transfer Across the Mina Deﬂ Ection

Origin and Evolution of the Sierra Nevada and Walker Lane themed issue

Pliocene sinistral slip across the Adobe Hills, eastern California–western Nevada: Kinematics of fault slip transfer across the Mina deﬂ ection

Sarah Nagorsen-Rinke1,*, Jeffrey Lee1, and Andrew Calvert2 1Department of Geological Sciences, Central Washington University, Ellensburg, Washington 98926, USA 2U.S. Geological Survey, Menlo Park, California 94025, USA

ABSTRACT faults are consistent with simple shear/couple wide deformation zone. The Mina defl ection clockwise block rotation within a broad dex- transfers slip northward onto northwest-striking The Adobe Hills region (California and tral shear zone. Vertical axis block rotation dextral faults of the central WLB (Figs. 1B and Nevada, USA) is a faulted volcanic fi eld data are needed to test this interpretation. 2). Thus, the Mina defl ection defi nes an east- located within the western Mina defl ection, We propose that a set of faults subparallel to northeast–trending right-stepping relay zone a right-stepping zone of faults that con- Sierra Nevada–North America motion and within a dominantly northwest-trending dextral nects the northern Eastern California shear associated releasing steps, located west of the shear zone. zone (ECSZ) to the south with the Walker White Mountains fault zone and east of Three mechanisms have been proposed to Lane belt (WLB) to the north. New detailed the Long Valley Caldera, transfer a portion explain the fault kinematics that accommodate geologic mapping, structural studies, and of dextral Owens Valley fault slip northwest- displacement transfer across the Mina defl ec- 40Ar/39Ar geochronology in the Adobe Hills ward onto the sinistral faults in the Adobe tion: (1) the displacement-transfer model (Fig. allow us to calculate fault slip rates and test Hills. Dextral slip distributed across faults 3A) (Oldow, 1992; Oldow et al., 1994), in which predictions for the kinematics of fault slip between the White Mountains fault zone and connecting faults transfer slip via normal slip; transfer into the Mina defl ection. The Adobe the Sierra Nevada and east of the Fish Lake (2) the transtensional model (Oldow, 2003) (Fig. Hills are dominated by Pliocene tuffaceous Valley fault zone may account for the appar- 3B), in which oblique (sinistral) normal slip sandstone, basaltic lavas that yield 40Ar/39Ar ent discrepancy between summed long-term occurs along the connecting faults; and (3) the ages between 3.13 ± 0.02 and 3.43 ± 0.01 Ma, geologic slip rates and present-day geodetic simple shear couple/fault block rotation model and basaltic cinder cones. These Pliocene rates across the northern ECSZ. Fault slip in (Wesnousky, 2005) (Fig. 3C), in which sinistral units unconformably overlie Middle Miocene the Adobe Hills is part of a regional pattern slip occurs along the connecting faults. Geo- latite ignimbrite that yields an 40Ar/39Ar age of initiation and renewal of dextral, sinistral, logic map relations, structural data, and seis- of 11.17 ± 0.04 Ma, and Quaternary tuffa- and normal fault slip during the Pliocene micity in the northern ECSZ, Mina defl ection, ceous sands, alluvium, and lacustrine depos- that extends from lat ~40°N to ~36°N within WLB, and Basin and Range Province led Oldow its cap the sequence. Northwest-striking nor- the ECSZ-WLB and along the western mar- (1992) and Oldow et al. (1994) to propose the mal faults, west-northwest–striking dextral gin of the Basin and Range Province. This displacement-transfer model for the Mina faults, and northeast-striking sinistral faults regional deformation episode may be related defl ection, whereby extension across northeast- cut all units; the northeast-striking sinistral to changes in gravitational potential energy. striking normal faults proportionally accom- faults are the youngest and most well devel- modates the magnitude of Middle Miocene to oped fault set. We calculate ~0.1 mm/yr of INTRODUCTION Pliocene dextral fault slip transferred between approximately east-west horizontal exten- the northern ECSZ and central WLB (Fig. 3A). sion and northwest dextral shear since the Geologic and geodetic studies indicate that Using a combination of global positioning sys- Pliocene. The prominent northeast-striking the San Andreas fault accommodates ~75%– tem velocities, earthquake focal mechanisms, sinistral faults offset basalt ridgelines, nor- 80% of relative dextral motion between the and fault-slip inversions, Oldow (2003) postu- mal fault–hanging-wall intersections, a Pacifi c–North American plates, and the East- lated that instantaneous deformation across the channelized basalt fl ow, a basalt fl ow edge, ern California shear zone (ECSZ)–Walker Mina defl ection region is currently accommo- and a basalt fl ow contact a net minimum of Lane belt (WLB) accommodates the remaining dated by transtension (Fig. 3B). In this model, 921 ± 184 to 1318 ± 264 m across the Adobe 20%–25% (Fig. 1A) (e.g., Dokka and Travis, deformation in the western Mina defl ection is Hills. These measured sinistral offsets yield 1990; Dixon et al., 1995, 2000; Bennett et al., characterized by extension-dominated trans- a minimum Pliocene sinistral fault slip rate 2003; Frankel et al., 2007; Lee et al., 2009a). tension, whereas the eastern part is character- of 0.2–0.5 mm/yr; our preferred minimum In the northern ECSZ, dextral shear is primar- ized by wrench-dominated transtension. Fault slip rate is 0.4–0.5 mm/yr. The geometry ily accommodated along four major northwest- geometries, sinistral offset, and paired basins at and orientation of the prominent sinistral striking dextral faults (Fig. 1B). These faults the ends of active east-northeast–striking faults transfer slip northward onto several smaller in the Mina defl ection led Wesnousky (2005) *Present address: Freeport-McMoRan Copper & primarily east-northeast–striking faults within to hypothesize that during the Holocene, fault Gold, P.O. Box 586, Bagdad, Arizona 86321, USA. the Mina defl ection, an ~125-km-long, ~45-km- blocks bounded by northeast-striking sinistral

Geosphere; February 2013; v. 9; no. 1; p. 37–53; doi:10.1130/GES00825.1; 10 ﬁ gures; 3 tables; 3 supplemental ﬁ les. Received 18 May 2012 ♦ Revision received 28 September 2012 ♦ Accepted 27 October 2012 ♦ Published online 11 January 2013

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GHF Figure 1. (A) Simplifi ed tectonic map of the western U.S. Cordillera showing the modern plate boundaries and tectonic provinces. Basin and PSF Range Province is in medium gray; Central Nevada seismic belt (CNSB), BSF eastern California shear zone (ECSZ), Intermountain seismic belt (ISB), Sierra Nevada CF Candelaria and Walker Lane belt (WLB) are in light gray; Mina defl ection (MD) is QVF Hills in dark gray. (B) Shaded relief map of the WLB and northern part of Mina the ECSZ showing the major Quaternary faults. Solid ball is located on deflection the hanging wall of normal faults; arrow pairs indicate relative motion 37° Bishop across strike-slip faults; white dashed box outlines location of Figure 2; light gray shaded areas show the Mina defl ection and the Carson WMFZ domain. BSF—Benton Springs fault; CF—Coaldale fault; DSF—Deep 117° Springs fault; DVFCFLVFZ—Death Valley–Furnace Creek–Fish Lake Silver Peak DSF Valley fault zone; GHF—Gumdrop Hills fault; HLF—Honey Lake fault; Fig. 2 area HMF—Hunter Mountain fault; MVF—Mohawk Valley fault; OVF— OVF

Owens Valley fault; PLF—Pyramid Lake fault; PSF—Petriﬁ ed Springs DVFCFLVFZ fault; QVF—Queen Valley fault; SLF—Stateline fault; SNFFZ—Sierra Nevada frontal fault zone; WMFZ—White Mountains fault zone; WRF—Wassuk Range fault; WSFZ—Warm Springs fault zone.

SNFFZ HMF SLF 36°

faults rotated clockwise in response to north- of ~74° and ~14° since the Miocene and Plio- suggesting that clockwise rotation is temporal west-dextral shear across the Mina defl ection cene, respectively (Rood et al., 2011). These and/or occurs in discrete zones within the Mina (Fig. 3C). Paleomagnetic studies in the eastern data suggest that the Wesnousky (2005) model defl ection. Mina defl ection imply clockwise rotation of is also applicable to older deformation within The results from new detailed geologic map- 20°–30° since Late Miocene to early Pliocene the Mina defl ection. In contrast, geologic stud- ping, kinematic, and 40Ar/39Ar geochronology time (Petronis et al., 2007, 2009), and paleo- ies centered on Quaternary faults in the Queen studies completed in the Adobe Hills, west- magnetic studies in the northwestern corner of Valley area did not yield evidence for recent ern Mina defl ection, are reported in this paper. the Mina defl ection indicate clockwise rotations clockwise block rotation (Lee et al., 2009b), These data allow us to test models for fault

38 Geosphere, February 2013

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slip transfer across the Mina deﬂ ection. From 119.00 118.75 118.50118.25 118.00

these data, we infer that a portion of dextral slip s in ta along the Owens Valley fault is transferred to n ou the sinistral faults in the Adobe Hills and that SN-NA M ior Pliocene deformation in the Adobe Hills is part Excels of a regional Pliocene event the length of the Figure 4 N ECSZ-WLB. Mono 38.00 Lake PS CF TECTONIC SETTING AND GEOLOGY Adobe y le Valley al OF THE ADOBE HILLS V CSF en Que QVF The Adobe Hills, an ~110 km2 faulted vol- Black Mountain canic ﬁ eld located east of the Sierra Nevada, Fish Lake

are located along the eastern edge of the Mono FLVFZ Valley Basin within the western Mina deﬂ ection (Figs. 37.75 Long 1B, 2, and 4). The Mina deﬂ ection is underlain Valley Wh

by Paleozoic miogeoclinal sedimentary rocks Benton Range

i te Mo and Mesozoic volcanic rocks and granitic plu- Volcanic Tableland WMFZ tons, Neogene ignimbrite, andesite, and basalt untains ﬂ ows, tuffaceous sediments, and volcanic brec- HCF cias, and Quaternary lacustrine and eolian sediments (e.g., Gilbert et al., 1968; Krauskopf and 37.50 RVF Bateman, 1977; Oldow, 1992; Reheis et al., 2002; Bradley, 2005; Tincher and Stockli, 2009; Petronis et al., 2009; Oldow et al., 2009; this

Sierra Nevada Bishop study). Structural, paleomagnetic, and strontium isotopic studies suggest that east-northeast– to Valley northeast-striking active sinistral faults within Deep Springs 37.25 the Mina deﬂ ection followed mid-Paleozoic to DSF

Mesozoic contractional structures, which fol- Owe

lowed the morphology of an embayment in the ns Vall O early Paleozoic rifted continental margin of the V F western U.S. (Oldow et al., 1989, 2009; Tosdal 25 km ey et al., 2000). Pliocene basaltic lavas and cinder cones form the Adobe Hills, interfi nger with lesser 37.00 early Pliocene lacustrine sediments, and over- Figure 2. Shaded relief map of the southern part of the Mina defl ection and northern part lie tilted Miocene latite ignimbrite fl ows, ande- of the eastern California shear zone showing the major Quaternary faults. Solid black ball sites, and volcanic breccias (Gilbert et al., 1968, is located on the hanging wall of normal faults; arrow pairs indicate relative motion across this study). Two episodes of deformation in the strike-slip faults. Heavy arrow in northwest corner of map shows the present-day motion Adobe Hills were noted by Gilbert et al. (1968) of the Sierra Nevada (SN) with respect to North America (NA) (Dixon et al., 2000). Loca- and our study: (1) pre-Pliocene deformation tion of the Adobe Hills geologic map shown in Figure 4A is outlined with a dashed line and marked by tilted and offset Miocene ignimbrite location of this map is shown in Figure 1. PS—Pizona Springs; CF—Coaldale fault; CSF— fl ows where the stratigraphic throw is larger Coyote Springs fault; DSF—Deep Springs fault; FLVFZ—Fish Lake Valley fault zone; than the throw of basalt fl ows, and (2) Pliocene HCF—Hilton Creek fault; OVF—Owens Valley fault; QVF—Queen Valley fault; RVF— to present deformation evidenced by normal, Round Valley fault; WMFZ—White Mountains fault zone. dextral, and sinistral faulting of Pliocene basalt fl ows. Extension and strike-slip faulting across the area has formed a complex ridge and valley morphology. Hills Spillway suggests that Pleistocene fault- Welded ignimbrite is exposed in the northern As part of a larger mapping project, Kraus- ing lowered topography and allowed southward Adobe Hills at the foothills of the Excelsior kopf and Bateman (1977) mapped the southern drainage of Pleistocene Lake Russell (Reheis Mountains, while a single outcrop of unwelded Adobe Hills at a 1:62,500 scale and documented et al., 2002). ignimbrite is exposed in the footwall of a normal welded latite tuff, basalt fl ows, and basalt scoria fault in the southern Adobe Hills (Fig. 4). Nearly cut by northwest-, north-south–, and northeast- GEOLOGIC ROCK UNITS AND AGES horizontal late Pliocene aphyric to phyric oli- trending normal faults. Reheis et al. (2002) vine + pyroxene– and plagioclase-bearing basalt completed a more detailed geologic map of The oldest unit exposed in the Adobe Hills fl ow cover ~80% of the Adobe Hills region and the western Adobe Hills that focused on Qua- comprises tilted Late Miocene welded and unconformably overlie tilted latite ignimbrite. ternary units, faults, and the Adobe Hills Spill- unwelded porphyritic plagioclase + biotite ± The relatively high standing exposure of Mlt in way bedrock channel. Formation of the Adobe augite–bearing latite ignimbrite (Figs. 4 and 5). the northeastern part of the fi eld area ( locality

Geosphere, February 2013 39

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A Normal faults of the Mina deflection boulder-sized clasts of basalt lava (a channelized rubble basalt fl ow) containing sector-zoned Dextral WLB faults pyroxene is exposed in the south-central part of the map area (Figs. 4A and 5). Lacustrine deposits and tuffaceous sandstones are locally interbedded with lower basalt fl ows; 13 Plio- cene red-weathering cinder cones overlie basalt fl ows. Quaternary sediments in the Adobe Hills include undifferentiated tuffaceous sands, playa deposits, basalt alluvium, landslides, and eolian deposits. Quaternary lacustrine deposits and Dextral ECSZ faults beach gravels are concentrated in the western Adobe Hills (Reheis et al., 2002). B Oblique-slip (sinistral and normal) faults of the Mina deflection 40Ar/39Ar Geochronology

Dextral WLB faults To constrain the age of basalt fl ows and faulting, and to calculate fault slip rates in the Adobe Hills, one ignimbrite sample and fi ve basalt samples were dated using 40Ar/39Ar incremen- tal heating techniques (Figs. 4A and 6; Table 1; Supplemental File 11). Analytical and data interpretation techniques are described in the Supplemental File (see footnote 1). Plagioclase separated from a welded latite ignimbrite from Dextral ECSZ faults the northeastern Adobe Hills (unit Mlt; sample AH09–41) yields an 40Ar/39Ar plateau age of C Sinistral faults of the Mina deflection 11.17 ± 0.04 Ma. Groundmass concentrates from samples of dense basalt fl ow interiors yield Dextral WLB faults either plateau ages or decreasing age spectra due to 39Ar recoil (Turner and Cadogan, 1974; Onstott et al., 1995). Recoil model ages for these recoil-affected samples are calculated by incor- porating age dispersion into the weighted mean age error, and are interpreted as the most reli- able ages. The oldest dated basalt fl ow, unit Pbc (sample AH09–42), collected on the same ridge Paired basins Dextral ECSZ faults as the dated welded ignimbrite, yields a plateau age of 3.43 ± 0.01 Ma. Two unit Pbo basalt fl ows were dated; one from the top of a normal fault– bounded ridge (sample AH08–35) yields a pla- Figure 3. Block diagrams illustrating models proposed to explain fault slip transfer across teau age of 3.28 ± 0.03 Ma, and the other from the Mina defl ection. (A) Displacement transfer model in which normal slip along connecting the base of the same ridge (sample AH09–201) faults transfers fault slip (modifi ed from Oldow, 1992; Oldow et al., 1994). (B) Transten- yields a recoil model age of 3.39 ± 0.03 Ma. The sional model showing a combination of sinistral and normal slip along connecting faults. channelized, rubble basalt fl ow, unit Pbr (sample (C) Clockwise block rotation model in which sinistral slip along connecting faults, combined AH08–19b), offset along a sinistral fault in the with vertical axis rotation of intervening fault blocks, transfers fault slip (modifi ed from south-central Adobe Hills, yields an 40Ar/39Ar McKenzie and Jackson, 1983, 1986). Single-barbed arrows show dextral fault motion across plateau age of 3.20 ± 0.03 Ma. The youngest faults of the Eastern California shear zone (ECSZ) and Walker Lane belt (WLB) and sinis- dated basalt fl ow, collected from unit Pbc at the tral motion along faults in the Mina defl ection; half-circle double-barbed arrows indicate top of a sinistral fault scarp in the northeastern clockwise rotating fault blocks; solid ball is located on the hanging wall of normal slip faults; Adobe Hills (sample AH08–33), yields a recoil thin short lines indicate slip direction on fault surfaces. model age of 3.13 ± 0.02 Ma. Our geochronologic data suggest that the basalt fl ows exposed across the Adobe Hills were emplaced over a of the 40Ar/39Ar sample that yields a 11.17 ± alogy and fl ow character, interfi nger across the short time period, <400 k.y. 0.04 Ma age; see following) and the curved Mlt- Adobe Hills. The source areas for these fl ows Pbo contact (Fig. 4) along both cross-sections were not observed. Basalt fl ows thin to the 1Supplemental File 1. PDF fi le of 40Ar/39Ar analytical techniques. If you are viewing the PDF of this suggest that Mlt had paleorelief prior to eruption north and northeast, where they mantle older paper or reading it offl ine, please visit http://dx.doi of the Pliocene basalt lavas (Fig. 4). Four differ- ignimbrite units (Fig. 4A) (Gilbert et al., 1968). .org/10.1130/GES00825.S1 or the full-text article on ent basalt fl ow units, mapped based on miner- A unique channel of subrounded cobble- to www.gsapubs.org to view Supplemental File 1.

40 Geosphere, February 2013

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/9/1/37/3344754/37.pdf by guest on 28 September 2021 Pliocene fault slip across the Adobe Hills Ar and ss. ss. 39 t olivine, olivine, Ar/ 40 ble flow ble flow gular red gular red , is white, , is white, of fault 2002). lude ~1% tted where where tted . 118.60°W l located (≤10m), l located 2 —Basalt lava rubble —Basalt lava r Pb 118.65°W —Undifferentiated basalt lava. basalt lava. —Undifferentiated Pb 1 ? ? 118.70°W SOURCE OF MAPPING 1. Sarah Nagorsen-Rinke and Lee. Jeffrey interpretation 2. Air photo Sarah Nagorsen-Rinke. 2002. 3. Reheis et al., 37.975°N 38.075°N 3 —Brown weathering, light to dark gray, flaggy, weakly (< 1%) phyric flaggy, dark gray, light to weathering, —Brown 118.75°W ignimbrite deposits variable in color. The unwelded ignimbrite underlies ignimbrite unwelded The deposits variable in color. ignimbrite Ar geochronology on basalt groundmass yields an age of 3.20 ± 0.03 Ma. on basalt groundmass Ar geochronology

Pbo 39 38.000°N 38.050°N 38.025°N Ar/ 40 slip, hachures on relative downthrown side; solid where wel side; solid where downthrown on relative hachures slip, 16 Eolian tuffaceous sand, fan deposits, and playa deposits following Reheis et al. (2002) Reheis et al. following deposits and playa fan deposits, sand, Eolian tuffaceous flow foliation flow White sand containing tabular pumice fragments up to ~ 8 mm, glass shards, and quartz ~ 8 mm, glass shards, grains. up to fragments tabular pumice sand containing White Tan to light orange weathering, tan to brown, fine- brown, poorly sorted,to medium-grained, tan to friable, moderately light orange weathering, to Tan Alternating beds of tan cross-bedded sandstones and white, silt-sized siliceous lake deposits underlying basalt siliceous silt-sized and white, sandstones beds of tan cross-bedded Alternating Ar geochronology on plagioclase yields an age of 11.17 ± 0.04 Ma for this unit. yields an age of 11.17 ± 0.04 Ma on plagioclase for Ar geochronology 39 —Brown to tan weathering, light to medium gray, weakly phyric (~ 1%) basalt lava. Phenocrysts (~ 1%) basalt lava. weakly of euhedral, consist phyric medium gray, light to tan weathering, to —Brown Angular basalt cobbles to boulders that define a hummocky to Angular basalt cobbles surface. 17 Unwelded to welded, biotite-bearing welded, latite to Unwelded Ar/

Angular basalt cobbles to boulders sourced up slope; common near fault scarps. up slope; common boulders sourced to Angular basalt cobbles 90 40 Red weathering, commonly cone-shaped volcanic center with smaller than pebble sized basalt cinder, pebble to pebble to basalt cinder, with smaller than pebble sized cone-shaped commonly center volcanic Red weathering, 30 White silt to mud-sized shallow-water playa deposits. deposits. playa shallow-water mud-sized silt to White White, chalky, massive carbonate deposits mantling basalts in the western Adobe Hills. Gravel-sized clasts and gastropod clasts and gastropod Gravel-sized Hills. Adobe deposits mantling basalts in the western carbonate massive chalky, White, Angular basalt cobbles to boulders and eolian tuffaceous sand that define a convex up, fan morphology. convex sand that define a boulders and eolian tuffaceous to Angular basalt cobbles Red and black scoria deposits ranging in size from near sand to cobble with scarce phenocrysts of olivine, pyroxene, and phenocrysts pyroxene, with scarce of olivine, cobble near sand to from in size deposits ranging Red and black scoria Attitudes

bedding 51 Ar geochronology on basalt groundmass records ages of 3.28 ± 0.03 Ma and 3.39 ± 0.03 Ma. records on basalt groundmass Ar geochronology 39 Fluvial sediments deposited upon basalt bedrock proximal to a channel. to proximal upon basalt bedrock sediments deposited Fluvial —Red to brown weathering, light to dark gray, phyric basalt lava. Phenocrysts basalt lava. of 5–10% glomerocrysts consist of euhedral to phyric dark gray, light to weathering, brown —Red to Ar/ 40 Pbc phenocrysts plagioclase (1–7 mm) and olivine (1–4 mm), trace (<1 mm) in a crystalline groundmass. subhedral pyroxene Basalt lava. Pbp Basalt lava. within a crystalline plagioclase translucent groundmass. (1–2 mm) in a microcrystalline groundma Phenocrystsbasalt lava. subhedral olivine (1–2 mm) and pyroxene of euhedral to consist geochronology on basalt groundmass yields ages of 3.13 ± 0.02 Ma and 3.43 ± 0.01 Ma. on basalt groundmass geochronology characterized by rounded cobble to boulder-sized clasts of black, vesicular, phyric basalt. Phenocrysts pyroxene, phyric include zoned clasts of black, boulder-sized to vesicular, cobble rounded characterized by crystalline in a coarse and plagioclase groundmass. Basalt colluvium. Tuffaceous sandstone. sandstone. Tuffaceous obsidian, clasts (1–4 mm), 3% angular and subrounded to subangular tabular pumice comprised of 10% angular sandstone tuffaceous lithics (1–2 mm). scoria Playa deposits. Playa Terrace. Eolian tuffaceous sand. Eolian tuffaceous sediments. Undifferentiated Fan deposits. deposits. Fan Landslide deposits. Beach gravel. high stands of Mono Lake (Reheis et al., early Pleistocene middle to represent to unit is interpreted This common. are fossils Basalt scoria. center. volcanic nearby from Sourced plagioclase. center. Volcanic blocks. breccia and vesicular bombs and blocks, cobble-sized and volcanic scoria, Lacustrine sediments. lavas. ignimbrite. Latite basalts in the southern Adobe Hills and is dark brown to ashy black, friable, and contains 4% subrounded basalt (4–5 mm), suban 4% subrounded black, and contains ashy friable, to Hills and is dark brown basalts in the southern Adobe Visi Minerals (1–2 mm). (<1 mm) and 0.5% subhedral plagioclase lithics. include 0.5% euhedral biotite (~3 mm), and wood granite in the northern basalt lavas which is a ridge-former Hills younger Adobe mantled by ignimbrite, welded The absent. are features Phenocrysts inc 30 mm in diameter. angular basalt lithics up to dark gray to with gray porphyritic in color, pink, or dark gray exhibi Some flows (1–2 mm) within an aphanitic groundmass. clear plagioclase to (1–2 mm) and ~1% gray euhedral-subhedral biotite eutaxitic texture. eutaxitic texture.

Ar sample location and age in Ma m Pb

27 5 Ar/ r 40 Q Qf Qt Qc Qe

Qp Qls Mlt Pts Pls Pbs Pvc Qlo Pbc Pbo Pbp

Pb dike Unit Q contact. magnitude of lateral offset of lateral magnitude Normal fault, ball and hachures on hanging wall; solid where well located (≤10m), dashed where approximately located (≤20m), do located approximately (≤10m), dashed where located well wall; solid where on hanging Normal fault, ball and hachures and plunge trend shows diamond-headed arrow fault plane dip direction and magnitude; Double-pronged indicates arrow concealed. striation. Solid where well-located (≤10m), dashed where approximately located (≤20m), dotted where concealed, queried where speculative. queried where concealed, where (≤20m), dotted located approximately (≤10m), dashed where well-located Solid where contact indicates dip direction and magnitude. Arrow sense of lateral relative indicate arrows Strike slip fault, paired concealed. where (≤20m), dotted located approximately dashed where

Pliocene Miocene Quaternary This map and explanatory information is submitted for publication with map and explanatory for This is submitted information to is authorized Government States the understanding that United use. governmental for reprints and distribute reproduce Geochronology Faults Intrusive rocks Intrusive Sedimentary and Volcanic Units Volcanic Sedimentary and Contacts EXPLANATION SYMBOLS ″ ″ 30 30 ′ ′ ′ ′ ′ 37°52 38°00 38°15 38°07 2 118°30 118°30' Spring Huntoon Valley ″ ″ Huntoon 30 30

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? 167 220 Q Pbo Pbc

40 Pbc ). (A) Geologic map of the Adobe Hills region (1:24,000 scale). See Figure 2 for location. Figure 4A is 4A location. Figure 2 for (1:24,000 scale). See Figure Adobe Hills region ). (A) Geologic map of the Q 100

3 Pbo Pbp ? 2 Qp Qf 15 Q

Mlt Mlt

0 fault 5 fault ? 4 Pvc Q

? Pts

230 Q

Qe ? Q Q 7 Q Pbc Pbp Q Pbo

Ma r Pbs Pvc

Pbo 100 Pbo

Pbc

ional 2 Pbo Pb Pbp 2

Pbc ns

Pbp 00 3.39

Qp ? 22 Qf Q 16

Stepove Exte Pbo

Qp 2

Q ? 281m Pbs

Pbc 00 3.28 Ma Pbo Q 30 Pts Q Q Qc

Pbo 23 Q

Pbc

Pvc ?

0 Q

? Pbo Pbp 14 0 Pbo Q

? 7 Qp 25 22 Qp

Pb Pb 0 Pbo Q 17 Pb Q

r Pb Qc 230 000

2 Pb Pbc Pb Pb Pbo Pvc Pressure Ridges Q 5 5 Pbs Qe Q 2 Pbo 8 Pbs

m Pvc Pbs Q 527 Pb Pbc 118.70°W Pbc Q A Pbo Pbc Q Pbc Figure 9c r Pvc Q Pbc Pbo ? 51 Pbo Pb Qp Q Pbs 4 Pvc Q Pbc 90 Pbo Qp 3.20 Ma 13 Pbo Pbc Pvc 37.975°N ? Qls 400 Pbc

2 Pbo Qc Qf Qp Pbp Pbs Pbc Q 38.075°N Pbc Pvc Q Q Pb Q Q Q Q Q Qp 12 Q Pb Pb Pb

Pbc Q 0

12 230 Q Q Pbo Pbo

Pbo B ? 00 0

2 0

r Pbo ? 2 2

ional 2

Pbo 2300 on this and following page on this and following Pbo

Pb ? ns 16 Qp Pbc

Stepove Exte 13 Q Q Pbo Q

2300 Q Pb Pvc Q Qp Pbo Pbp Pbo Q 11

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Pbp 00 Figure 4 ( Figure view the full-sized ﬁ To intended to be viewed at a width of 38.3 in. Q Qf

3 23 Qlo Pbo Qp Pb Q 11 Q Q

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0 220 Pb Pvc Qlo CALIFORNIA – NEVADA CALIFORNIA Q Pb Pb Pb Q Q 118.75°W Pb GEOLOGIC MAP OF THE ADOBE HILLS OF THE GEOLOGIC MAP Q Q 38.000°N 38.050°N 38.025°N A

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2500 2250 2000 FAULTS IN THE ADOBE HILLS ′ A Pbo Mlt U Pbc North-northwest–striking normal faults, west- Southeast D

Q northwest–striking dextral faults, and northeast- striking sinistral faults cut and offset Miocene ignimbrite ﬂ ows, Pliocene sediments and basalt Q ﬂ ows, and some Pliocene cinder cones (Figs. 4 Q and 7). Fault scarps are primarily characterized Qt Mlt Pbc

Q by nearly vertical faces that expose ﬂ ow features within basalt, and slickenlines are rare. Seis- of 23.6 in. To To of 23.6 in. 2000 1800 1600 2200 Pbo micity in the area indicates that faults are still ′ B East active (Ryall and Priestly, 1975; Rogers et al., Q Pbo Mlt U 1991; dePolo et al., 1993); however, ash fallout D Pbc and wind-blown volcanic glass, ash, and small Q Pbc Pbo U

Pbo lithics from Mono and Inyo Craters obscure D Q latest Pleistocene and Holocene fault scarps, if Qc

Pbo developed. Reheis et al. (2002) noted that some Q fresh fault scarps are exposed in the western Mlt

Q Adobe Hills. Pbc Pbo Q

D Fault Geometry and Geomorphology U D Pbo U Q Although a small data set, tilted bedding and Pbs Mlt Pbo ﬂ ow foliation measurements within Mlt along Mlt

Pbc with paleorelief on Mlt suggest an episode of ′ ′ Q

Pbp deformation prior to eruption of the Pliocene U U D basalt lavas. Map, structural, paleomagnetic, Pbo D and geochronologic data reveal Late Miocene Q Mlt Pbo V = 2H V = H east-west extension, dextral slip, and verti- Q Pbs cal axis rotations within the central WLB and Pbo Adobe HillsAdobe Cross-Section A–A Adobe Hills Cross-SectionAdobe B–B

Mlt northern ECSZ (e.g., Dilles and Gans, 1995; Mlt Mlt Pbo U Pbo Stockli et al., 2003; Tincher and Stockli, 2009; D Q Mlt Pbo Pbc Rood et al., 2011), indicating that the region ? Pvc Mlt Q

Pbo underwent deformation at that time. This U D D Pbp U U Pbo deformation episode combined with erosion Pvc D likely resulted in the paleorelief along the Q Pbc

Mlt unconformity between Mlt and the overlying Pbr

Q Pliocene lavas (Fig. 4). However, because of D

U the limited exposure of Mlt, the nature of this Qls Late Miocene deformation in the Adobe Hills Mlt Pbo Q Pbc Mlt area is not known.

QQ The oldest set of faults are north-south- to , (2) the two cross sections are not at the same scale, and (3) both cross sections are at a smaller scale than at a smaller sections are not at the same scale, and (3) both cross sections are , (2) the two cross ′ D

U northwest-striking curvilinear to straight normal faults that are ~0.2–2 km in length and B Pbs 10–130 m in fault scarp height (Figs. 4 and 7). West

2200 2000 1800 1600

? Evidence for normal faulting includes linear to Pvc (meters) Elevation moderately curved valleys in conjunction with ). (B) Interpretative northwest-southeast and east-west cross sections. Note that (1) vertical scale is two times the hori- northwest-southeast and east-west cross ). (B) Interpretative please visit http://dx.doi.org/10.1130/GES00825.S3. gure, vertically offset basalt ﬂ ows and exposed Mio-

Pbs cene ignimbrite fl ows and Pliocene sandstone in the footwall of faults. In the southern Adobe Q continued Hills, normal faults strike northwest near the trace of fault 3 and strike north with increasing Mlt distance away from this fault (Figs. 4A and 7). Figure 4 ( Figure A–A cross-section zontal scale for the geologic map shown in A (see A for section locations and unit descriptions). Figure 4B is intended to be viewed at a width section locations and unit descriptions). Figure for A (see A the geologic map shown in view the full-sized fi Some normal faults in the Adobe Hills are sinis- Pbc Pbo trally or dextrally offset, while others defi ne left

Q steps along sinistral faults (Figs. 4A, 7, and 8). D

U All normal faults displace late Pliocene basalt A Pbc Mlt Pbo ﬂ ows and older units; therefore, all normal fault- Northwest

2500 2000 2250 ing postdates Pliocene basalt volcanism, and Elevation (meters) Elevation

B mostly predates sinistral faulting.

42 Geosphere, February 2013

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Pbs (basalt scoria)–Red and black, angular to subrounded deposits of scoria clasts ranging in size from near sand to cobble with scarce phenocrysts of olivine, pyroxene, and plagioclase. Sourced from nearby volcanic center.

Pvc (volcanic center)–Red weathering, commonly cone-shaped volcanic center with smaller than pebble sized basalt cinder, pebble to cobble-sized scoria, and volcanic bombs and blocks, and vesicular breccia blocks.

Pbr (basalt lava rubble)–Rounded cobble to boulder-sized clasts of black, vesicular, phyric basalt which contains oscillatory and sector zoned pyroxene, olivine, and plagioclase phenocrysts in a coarse crystalline groundmass. 40Ar/39Ar geochronology on basalt groundmass yields an age of 3.20 ± 0.03 Ma.

Pliocene Pbp, Pbc, and Pbo (interfingered basalt lava flows). Pbp–Brown to tan weathering, light to medium gray, weakly phyric (~1%) basalt lava contains euhedral, translucent plagioclase phenocrysts within a crystalline groundmass. Pbc–Red to brown weathering, light to dark gray, phyric basalt lava contains 5–10% glomerocrysts of euhedral to subhedral pyroxene (1–7 mm), olivine (1–4 mm), and trace plagioclase phenocrysts (<1 mm) in a crystalline groundmass. 40Ar/39Ar geochronology on

50 m basalt groundmass records ages of 3.13 ± 0.02 Ma stratigraphically high within this unit and 3.43 ± 0.01 Ma at the base of the unit. Pbo–Brown weathering, light to dark gray, flaggy, aphryic to weakly phyric (< 1%) basalt lava contains euhedral to subhedral olivine (1–2 mm) and pyroxene (1–2 mm) phenocrysts in a microcrystalline groundmass. 40Ar/39Ar geochronology on basalt groundmass records ages of 3.28 ± 0.03 Ma at a ridge top and 3.39 ± 0.03 Ma at the base of this ridge.

Pts (tuffaceous sandstone)–Exposed in the southern Adobe Hills, this tan to light orange weathering, tan to brown, fine- to medium-grained, poorly sorted, moderately friable, tuffaceous sandstone is comprised of 10% angular to subangular tabular pumice clasts (1–4 mm), 3% angular and subrounded obsidian, and scoria lithics (1–2 mm).

Pls (lacustrine sediments)–Locally exposed sequence of alternating beds of tan to brown, cross-bedded volcaniclastic sandstone, white diatomite, and mudstone interfingered with palagonitized basalt flows. Friable volcaniclastic sandstone interbeds range from 18–23 cm thick, are moderately sorted, and are composed primarily of basalt clasts and volcanic glass. Chalky, thick-bedded (up to 2.1 m) diatomite contains leaf fossils and fresh water diatoms.

Mlt (latite ignimbrite)–Unwelded dark brown to ashy black, friable ignimbrite exposed in the southern Adobe Hills contains 4% lithics comprised of subrounded basalt (4–5 mm), subangular

Miocene red granite (~3 mm), and wood, and 0.5% euhedral biotite (<1 mm) and 0.5% subhedral plagioclase (1–2 mm). Visible flow features are absent. The ridge-forming, porphyritic, welded white, pink, or dark gray ignimbrite exposed in the northern Adobe Hills contains gray to dark gray angular basalt lithics up to 30 mm in diameter and ~1% euhedral-subhedral biotite (1–2 mm), ~1% gray to clear plagioclase (1–2 mm), and trace augite phenocrysts. Some flows exhibit eutaxitic texture. Ignimbrite flows range in dip from 50° to 86° towards the E and SE. 40Ar/39Ar geochronology on plagioclase yields an age of 11.17 ± 0.04 Ma for this unit.

Figure 5. Stratigraphic column of Miocene and Pliocene volcanic and sedimentary rocks exposed in the Adobe Hills. Relative thicknesses are shown.

A few northwest-striking, right-lateral faults, ranging from 6 to 12 km in fault trace length and facing directions along fault strike, left-stepping exposed near the southern boundary of the Adobe tens of centimeters to ~100 m in scarp height extensional (Fig. 8) and right-stepping compres- Hills (Figs. 4A and 7), are the least abundant fault (Figs. 4 and 7). Sinistral faults traverse nearly sional stepovers, and sinistrally offset normal type. These faults offset normal faults, but not the entire fi eld area, are well defi ned in the cen- fault–hanging-wall surface intersections, ridge- sinistral faults; therefore, dextral faulting occurred tral, northern, and eastern areas, and become lines, contacts, and channelized fl ows (Figs. after normal faulting and before sinistral faulting. more diffuse toward the south and southwest, 4A, 7, and 9). Linear valleys in conjunction The youngest and most prominent faults in the where they are represented by several en eche- with fault scarps tens of centimeters to 100 m in Adobe Hills are fi ve major and numerous minor lon short fault strands. Sinistral faults are char- height along the sinistral fault traces may indi- northeast-striking near-vertical sinistral faults, acterized by linear valleys, alternating scarp cate that these faults also accommodated a small

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14 5.0 Unit Mlt (AH09-41 plagioclase) Unit Pbc (AH09-42 groundmass basalt flow)

13 4.5

WMPA = 3.43 ± 0.01 Ma 12 WMPA = 11.17 ± 0.04 Ma 4.0 (81.41% 39Ar released; MSWD = 1.92) (96.29% 39Ar released; MSWD = 1.36) Apparent Age (Ma) 11 Apparent Age (Ma) 3.5

10 3.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Cumulative 39Ar Released Cumulative 39Ar Released

Figure 6. Age spectra for plagio- 4.0 4.0 Unit Pbo (AH09-201 groundmass basalt flow) Unit Pbo (AH08-35 groundmass basalt flow) clase within ignimbrite and groundmass concentrate within 3.5 3.5 basalt ﬂ ows. Summary of ages is

shown in Table 1 and analytical 3.0 3.0 data are listed in Supplemen- tal File 1 (see footnote 1). Unit Recoil Model Age = 3.39 ± 0.03 Ma 39 Apparent Age (Ma) (100% Ar released; MSWD = 10.54) Apparent Age (Ma) descriptions are in Figures 4A 2.5 2.5 WMPA = 3.28 ± 0.03 Ma and 5. WMPA—weighted mean (64.74% 39Ar released; MSWD = 0.35) plateau age; MSWD—mean 2.0 2.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 square of weighted deviates. Cumulative 39Ar Released Cumulative 39Ar Released

5.0 4.0 Unit Pbr (AH08-19b groundmass basalt flow) Unit Pbc (AH08-33 groundmass basalt flow) 4.0 3.5

3.0 3.0 2.0 Recoil Model Age = 3.13 ± 0.02 Ma WMPA = 3.20 ± 0.03 Ma (100% 39Ar released; MSWD = 7.93) (83.26% 39Ar released; MSWD = 0.39) Apparent Age (Ma) Apparent Age (Ma) 2.5 1.0

0.0 2.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Cumulative 39Ar Released Cumulative 39Ar Released

component of extension in addition to the domi- Magnitude of Fault Slip and of vertically displaced marker beds, we esti- nant sinistral offset. However, two ﬁ eld observa- Fault Slip Rates mate a minimum approximately east-west hori- tions imply that the magnitude of extension is zontal extension magnitude along transect A likely negligible: (1) fault traces are linear and The north-south- to northwest-striking nor- (Fig. 7), using the height of exposed fault scarps crosscut topography, suggesting nearly vertical mal faults in the south-southwestern Adobe and assuming a fault dip of 60°. The transect fault dips (80°–90°), and (2) the fault scarps Hills suggest this area underwent approxi- records a minimum vertical offset of 495 m, change facing direction along strike, suggesting mately east-west–directed extension over a which, along with the range of basalt ages of that this geometry is the result of sinistral fault rela tively short period of geologic time, after 3.13 ± 0.02 to 3.43 ± 0.01 Ma, yields a mini- slip along a nearly vertical fault that juxtaposed late Pliocene basalt emplacement, but before mum horizontal extension rate of ~0.1 mm/yr. topographic lows against topographic highs. Pliocene sinistral faulting began. In the absence The rate of approximately east-west extension

TABLE 1. SUMMARY OF 40Ar/39Ar AGES Plateau Isochron Age Age 39Ar σ σ 40 36 σ Sample Unit Coordinates (Ma) ±1 MSWD (Ma) ±1 Ar/ Ari ±1 MSWD (%) AH09-41 Mlt 38°3.6400, 118°37.6116 11.17 0.04 1.92 11.17 0.03 300.4 11.8 1.89 81.4 AH09-42 Pbc 38°3.6816, 118°37.5750 3.43 0.01 1.36 3.41 0.01 299.7 3.2 1.06 96.3 AH09-201 Pbo 38°0.1812, 118°41.0100 3.39* 0.03 10.54 3.41 0.03 291.3 6.9 10.54 100.0 AH08-35 Pbo 38°0.1140, 118°41.2350 3.28 0.03 0.35 3.38 0.09 294.1 2.5 0.59 64.7 AH08-19b Pbr 38°0.7464, 118°41.6280 3.20 0.03 0.39 3.33 0.09 294.1 1.9 0.64 83.3 AH08-33 Pbc 38°3.6906, 118°36.1794 3.13* 0.02 7.93 3.14 0.02 295.4 5.5 10.70 100.0 Note: See Figures 4 and 5 for unit descriptions. MSWD—mean square of weighted deviates. *Recoil model age. Supplemental data and detailed methodology are in Supplemental File 1 (see text footnote 1).

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5 fault 38.075°N fault 4 extensional stepovers fault 3

fault 2

compressional 401 m stepover 294 m n Hu to on

C ree k 38.050°N lt 1 fau extensional stepovers

transect C

225m 38.025°N extensional stepover

167 m 268m 151 m 205 m

7m 52

38.000°N transect B transect A N 281m 012 pressure ridges kilometers

118.75°W 118.70°W 118.65°W 118.60°W

Figure 7. Faults from the geologic map of the Adobe Hills (see Fig. 4A) compiled on digital orthophotographs highlighting primary sinistral fault zones and locations of measured lateral offset. Normal faults are shown in white; sinistral and dextral faults are shown in black. Solid ball, hachures, and paired arrows are deﬁ ned in Figure 2. See text for discussion of slip calculations along transects.

could be an order of magnitude higher if this emplacement and onset of sinistral faulting, an 40Ar/39Ar basalt age range of 3.28 ± 0.03– extensional episode, bracketed between basalt were a few hundred thousand years. 3.39 ± 0.03 Ma, yields a minimum sinistral slip emplacement and onset of sinistral faulting, The youngest, longest, and most prominent rate of ~0.1 mm/yr for this fault (Table 2). This were a few hundred thousand years. sets of faults exposed across the fi eld area are slip rate is similar or less than rates along the Dextral faults are limited to the southern fi ve major northeast-southwest–striking sinis- other sinistral faults within the Adobe Hills (see Adobe Hills and offset normal faults, but do not tral fault zones. Measurable sinistral offset following), which suggests to us that the mea- offset sinistral faults. One northwest-striking magnitudes along individual fault strands range sured apparent 268 m sinistral offset of the Pbs- dextral fault in the southern Adobe Hills offsets from 151 to 527 m and calculated minimum slip Pbo contact is reasonably accurate. a normal fault–hanging-wall surface intersec- rates along individual fault zones range from 0.1 Evidence for the magnitude of sinistral offset tion lineation and Pbo basalt ridgeline by 281 ± to 0.2 mm/yr (Figs. 4A, 7, and 9; Table 2). along fault 2 is exposed along its northeastern 42 m. This offset measurement, combined with Fault 1, located in the southeastern Adobe trace and a set of splays along its southwestern an 40Ar/39Ar basalt age range of 3.28 ± 0.03– Hills, offsets a Pbc basalt fl ow edge and a con- trace. In the northeast, the fault consists of two 3.39 ± 0.03 Ma for unit Pbo, yields a minimum tact between a scoria deposit (Pbs) and underly- splays that sinistrally offset units Pbc and Pbo dextral slip rate of ~0.1 mm/yr. Like the east- ing Pbo basalt fl ow 225 ± 33 m and 268 ± 54 m, and the intersection line defi ned by a northeast- west extension rate, the rate of dextral shear respectively. The latter may be an apparent off- dipping normal fault and the subhorizontal sur- could be an order of magnitude higher if this set because the contact between Pbs and Pbo is face of its hanging-wall basin a total of 695 ± deformation episode, bracketed between basalt shallow. Fault offset magnitude, combined with 139 m (Figs. 4A, 7, and 9A). This offset measure-

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slip to a lesser extent also occurred along older NW SE north-south– to north-northwest–striking normal faults and northwest-striking dextral faults. All faults cut Pliocene basalts and older units, and likely Quaternary deposits (Fig. 4A). We calculate a minimum Pliocene sinistral fault slip rate of 0.2–0.5 mm/yr across the Adobe Hills; our preferred minimum sinistral slip rate is 0.4– 0.5 mm/yr. Calculated minimum Pliocene west- northwest–east-southeast extension rates across Excelsior Mountains older normal faults and northwest dextral fault Huntoon Valley slip rates are both ~0.1 mm/yr. Pb The Mina defl ection defi nes a right step between the northwest-striking dextral faults in the northern ECSZ and the northwest-striking Pb Qp dextral faults exposed in the central WLB (Figs. 1B and 2). The prominent northeast-striking Q sinistral faults in the Adobe Hills are exposed in the southwestern part of this right step. A similar geometric confi guration exists in the Carson domain of the central WLB (see gray shaded area southeast of Reno; Fig. 1B), an ~2420 km2 zone of northeast-striking sinistral faults that transfers dextral slip between northwest-striking Pyramid Lake, Warm Springs Val- ley, and Honey Lake dextral faults exposed to Figure 8. Field photograph of a playa formed in an extensional stepover or releasing bend the north and northwest-striking Gumdrop Hill, along a left-stepping sinistral fault. Paired arrows show relative strike-slip fault motion; Benton Springs, and Petrifi ed Springs dextral solid ball is on the hanging wall of the normal fault. Q—undifferentiated Quaternary sedi- faults exposed to the south (Cashman and Fon- ments; Qp—Quaternary playa deposits; Pb—undifferentiated Pliocene basalts. taine, 2000) (Fig. 1B). Paleomagnetic data from the Carson domain indicate that dextral fault slip transfer has occurred via ~55° to ~11° of ment, combined with ages for the top and bot- We infer, therefore, that the Pliocene sinistral Miocene to Pliocene clockwise block rotation tom of a nearby offset Pbc basalt fl ow of 3.13 ± slip rate along both faults 4 and 5 is ~0.1 mm/yr. (Cashman and Fontaine, 2000). 0.02 Ma and 3.43 ± 0.01 Ma, yields a minimum Because we can measure offsets on only 3 Clockwise rotation of blocks has been also sinistral slip rate of 0.2–0.3 mm/yr (Table 2). A of the 5 major sinistral fault zones, our calcu- documented in the eastern, southeastern, and zone of three small (0.4–1 km long) subparallel lated net sinistral offsets across transects B and northwestern parts of the Mina defl ection. sinistral faults offsets units Pbc and Pb along the C of 921 ± 184 m and 1318 ± 264 m (Fig. 7; Petronis et al. (2009, 2007) documented block southwestern segment of fault 2 (Figs. 4A, 7, and Table 3), respectively, are minimum estimates. rotations of 20°–30° and 20°–25° since the Late 9B). Here, the total offset of the intersection line Combining these measurements with the age Miocene to early Pliocene in the Candelaria between normal faults and surface of hanging- range of basalt fl ows of 3.13 ± 0.02 Ma to 3.43 ± Hills (eastern Mina defl ection) and the Silver wall basins, and a basalt ridgeline across the three 0.01 Ma yields a minimum net sinistral slip rate Peak area (southeast of the Mina defl ection; faults, is 523 ± 78 m. This offset measurement, of between 0.2 and 0.5 mm/yr. If our assess- Fig. 1B). Similarly, in the Bodie Hills region combined with a basalt 40Ar/39Ar age range of ments that the expression of sinistral faults 4 northwest of Mono Lake Basin and northwest 3.13 ± 0.02–3.43 ± 0.01 Ma, yields a minimum and 5 is similar to fault 1, but less so than faults of the Mina defl ection (Fig. 1B), paleomagnetic slip rate of 0.1–0.2 mm/yr (Table 2). 2 and 3, are valid and each records fault slip rates studies indicate clockwise rotations of ~74° and Evidence for magnitude of sinistral offset of ~0.1 mm/yr, we suggest that 0.4–0.5 mm/yr ~14° since the Miocene and Pliocene, respec- along the trace of fault 3 is exposed toward its is a reasonable estimate for a minimum Pliocene tively (Rood et al., 2011). southwestern end (Figs. 4A, 7, and 9C). Fault 3 sinistral slip rate across the Adobe Hills. Northeast-striking right steps between dex- sinistrally offsets a distinct channelized rubble tral systems are documented elsewhere in the basalt fl ow (unit Pbr) 527 ± 79 m. Combin- DISCUSSION northern ECSZ, and include the Queen Valley, ing this offset with an 40Ar/39Ar age of 3.20 ± Deep Springs, Towne Pass, and numerous other 0.03 Ma for this basalt unit yields a minimum Mechanisms of Fault Slip Transfer across normal faults that transfer dextral slip from the late Pliocene sinistral slip rate of ~0.2 mm/yr the Mina Defl ection Owens Valley and Hunter Mountain–Panamint (Table 2). Valley fault zones to the Death Valley–Fish Lake We did not observe offset geologic markers The Adobe Hills area, located in the south- Valley fault zone (Figs. 1B and 2) (e.g., Lee along sinistral faults 4 and 5 (Fig. 4A). However, western part of the Mina defl ection, accommo- et al., 2009b, 2001; Reheis and Dixon, 1996; the geomorphic expression for these two faults dated late Pliocene to Holocene fault slip. Five Sternlof, 1988). These faults are unlike those in is as well developed as fault 1, but somewhat geomorphically prominent northeast-striking the Adobe Hills area and Carson domain in that less well developed compared to faults 2 and 3. sinistral fault zones dominate the region. Fault they act as right-stepping releasing bends and

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1950 38.065°

2050

2000 2050 401 m 2050 3.43 Ma 2000 294 m 2100 2100

3.13 Ma 2100

2050 2000

38.055°

2050 118.6225 118.6125 118.6025 118.5925

B 400 m 2150 N

220 0 contour interval 5 m

2150 38.020° C 38.010° 2250 167 m 2250 2150 2200 150 m 2200 3.20 Ma Pb 152 m r

38.015° Pbr 527 m 2150 205 m 2150 38.005°

200 2 118.7025° 118.6925° 118.675° 118.670° 118.665°

Figure 9. Detailed fault maps superimposed on digital orthophotographs and digital elevation map–generated contours showing left-lateral offset of geologic features along sinistral faults 2 and 3 (see Fig. 7). (A) The intersection line of a normal fault and the surface of its hanging- wall basin are sinistrally offset twice for a total of ~695 m along the northeastern segment of fault 2. (B) The southwestern segment of fault 2 is characterized by several subparallel sinistral fault strands that offset the intersection of line of normal faults and hanging-wall basins, and a basalt ridgeline (narrow dashed line). The net offset across these sinistral faults is ~523 m. (C) The edge of the basalt rubble ﬂ ow, unit Pbr (see Figs. 4A and 5 for description), is sinistrally offset ~527 m by fault 3. Paired arrows, solid ball, and hachures are deﬁ ned in Figure 4A, and locations are shown in Figure 4A.

transfer dextral fault slip via normal faulting. the central WLB. Each model was developed northern ECSZ to the central WLB during the None of these faults shows geologic evidence for a particular time period and taken together Middle Miocene to Pliocene (Fig. 3A) (Oldow, (e.g., oblique slip) for vertical axis rotation. imply that the mechanism of fault slip transfer 1992; Oldow et al., 1994). In the Adobe Hills Three fault kinematic models have been has changed through time. In the displacement- region, the north-to-northwest strikes of normal proposed to explain the mechanisms by which transfer model, curved northeast-striking normal faults do not fi t the northeast-striking geometry dextral fault slip is transferred from the north- faults in the Mina defl ection accommodated the required of this model, and the northeast-strik- ern ECSZ through the Mina defl ection and into magnitude of dextral fault slip transfer from the ing faults record sinistral slip with little or no

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TABLE 2. SINISTRAL FAULT SLIP RATES with the simple shear couple/fault block rota- Age Sinistral offset§ Slip rate tion model (e.g., McKenzie and Jackson, 1983, Fault* Offset marker† (Ma) (m) (mm/yr) 1986; Wesnousky, 2005) (Fig. 3C). It is there- 1Pbc fl ow edge 3.13 ± 0.02 to 3.43 ± 0.01 225 ± 34 0.1 1 Pbs/Pbo contact 3.28 ± 0.03 to 3.39 ± 0.03 268 ± 54 0.1 fore likely that fault blocks bounded by sinis- 2 normal fault 3.13 ± 0.02 to 3.43 ± 0.01 695 ± 139 0.2–0.3 tral faults in the Adobe Hills fault zone rotated 2 normal fault; ridge 3.13 ± 0.02 to 3.43 ± 0.01 523 ± 78 0.1–0.2 3 Pbr lava 3.20 ± 0.03 527 ± 79 0.2 clockwise during fault slip. Additional data are *See text for fault descriptions. needed to characterize fault kinematics, particu- †See Figures 4, 7, and 9 for locations of offset markers. See Figures 4 and 5 for descriptions of Pbc, Pbs, Pbo, larly vertical axis fault block rotation data from and Pbr. paleomagnetic studies, to test the mechanisms §Measurements were made in the fi eld using a handheld global positioning system unit or measured on a 1:12,000 geologic map. If the intersection of a fault and offset marker is well defi ned, a conservative uncertainty of fault slip transfer across the western Mina of 15% was applied; if the intersection is not well defi ned, an uncertainty of 20% was applied. defl ection.

Kinematics of Fault Slip Transfer into the normal slip. Therefore, this model is not applica- apart strike ~N40°E, while major sinistral faults Western Mina Defl ection ble to this part of the Mina defl ection. in the eastern Mina defl ection strike more east In the transtensional model, instantaneous (N60°–90°E). Furthermore, none of the sinistral Field-based studies of faults in Queen Val- fault slip today across the western Mina defl ec- faults in the Adobe Hills is a single, throughgo- ley, located in the southwestern part of the Mina tion is characterized by extension-dominated ing structure; rather, they are characterized by defl ection (Figs. 1A and 2), led to a proposal transtension, and across the eastern part is en echelon segments and splays. With continued (Lee et al., 2009b) of a kinematic fault slip characterized by wrench-dominated transten- displacement, the en echelon fault segments and model whereby 0.8–0.4 mm/yr of Pliocene to sion (Oldow, 2003) (Fig. 3B). In the Adobe splays might coalesce into single, throughgoing Pleistocene dextral fault slip was transferred Hills, north-northwest–striking normal faults sinistral faults (e.g., Wesnousky, 2005). Some northward from the White Mountains fault are exposed in the southwestern part of the of the sinistral faults centered on the Adobe zone onto sinistral faults in the western Mina Adobe Hills and accommodate a minimum Hills exhibit paired basins, consistent with the defl ection via the dextral Coyote Springs fault of ~0.1 mm/yr of horizontal extension, a rate model. For example, north of Huntoon Creek, (Fig. 2). The Adobe Hills, across which we have smaller than the minimum sinistral fault slip sinistral fault scarps along faults 2, 3, and 4 gen- documented a minimum late Pliocene sinistral rate (although see discussion in Magnitude of erally face northwest and basins are developed slip rate of 0.4–0.5 mm/yr, is located west of the Fault Slip and Fault Slip Rates section regarding on the northwest side of the fault traces (Figs. northwest projection of the Coyote Springs fault the possibility of an order of magnitude higher 4A and 7), as predicted by the model (Fig. 3C). (Fig. 2). The Pizona Springs area, located east extension rate), and are older than the sinistral However, our reconnaissance mapping suggests and southeast of the Adobe Hills (Fig. 2), is at faults. Thus, in the Adobe Hills extensional that the northeastern fault tips are beyond the the northwestern tip of the Coyote Springs fault. and transcurrent deformation episodes were fi eld area. At the southern tips of sinistral faults In this area, geomorphically prominent sinistral partitioned in space and time, and transcurrent 2 and 4, fault scarps face southeast and basins faults are subparallel to and as well developed fault slip was the dominant deformation style. are developed on the southeast side of the fault as the ones we have documented in the Adobe We conclude that the extension-dominated traces, as also predicted by the model (Fig. 3C). Hills, and cut basalt and andesite fl ows (J. Lee, transtension model proposed for instantaneous The southern tip of fault 3 faces northwest with 2010, personal observations and mapping; fault slip transfer today across the western Mina a basin on its northwest side, in contrast to faults E. Hogan, 2012, personal commun.) (Fig. 2). defl ection was not the style of deformation that 2 and 4. Thus, sinistral faults in the Adobe Hills We therefore speculate that the Pliocene sinistral resulted in the types and geometries of faults have some of the features predicted by the fault slip rate along each sinistral fault in the Pizona exposed across the Adobe Hills region. block rotation model, but not all. The complex- Springs area is ~0.1–0.2 mm/yr, the same as we In the simple shear couple/fault block rota- ity of fault geometries in the Adobe Hills (Figs. have documented along sinistral faults in the tion model (Wesnousky, 2005) (Fig. 3C), east- 4A and 7) suggests that, if fault block rotation Adobe Hills. If the predicted ~0.8–0.4 mm/yr northeast–striking sinistral faults spaced 10 km occurred, it likely occurred at a scale of fault fault slip transfer rate is correct, and the Coyote apart in the Mina defl ection rotated ~20°–30° blocks spaced 0.3–1 km apart as compared to Springs fault abuts these sinistral faults, then the clockwise during the Holocene from an original more widely spaced (~10 km) large fault blocks Pizona Springs area of the western Mina defl ec- orientation nearly perpendicular to dextral faults bounded by the primary sinistral faults of the tion accommodated transfer of dextral slip from of the northern ECSZ and central WLB. Paired Mina defl ection (Figs. 1A and 2). the White Mountains fault zone; those in the basins on the northeast and southwest ends of Although exposed fault striations are rare Adobe Hills did not. sinistral faults may have formed as a conse- along the sinistral faults in the Adobe Hills, the This raises the question, what system of faults quence of extension at the tips of sinistral faults geometry and orientation of these faults with in the northern part of the ECSZ transfers slip during rotation between bounding northwest- respect to the northwest-striking dextral faults onto the sinistral faults of the Adobe Hills? striking dextral faults (Wesnousky, 2005). Sinis- that defi ne the northern ECSZ to the south and Based on the orientation of dextral and normal tral faults in the Adobe Hills spaced 0.3–1 km the central WBL to the north are consistent faults with respect to small circles about the Sierra Nevada–North American Euler pole and kinematic inversions of earthquake focal mech- TABLE 3. MINIMUM NET SINISTRAL FAULT SLIP RATES anisms, Unruh et al. (2003) postulated that nor- Sinistral offset Age Slip rate Transect* (m) (Ma) (mm/yr) mal faults in this region were the result of plate B 921 ± 184 3.13 ± 0.02 to 3.43 ± 0.01 0.2–0.3 boundary–driven northwest translation of the C 1318 ± 264 3.13 ± 0.02 to 3.43 ± 0.01 0.3–0.5 Sierra Nevada microplate. Furthermore, Unruh *See Figure 7 for locations of transects. et al. (2003) noted that major grabens along the

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northeastern ﬂ ank of the Sierra Nevada deﬁ ne a 0.6 westward-stepping fault array, and thus a releas- 118.75 0.2 118.50 118.25 ing step with respect to Sierra Nevada–North 0.5-0.6 American motion. Following Unruh et al.’s SN-NA (2003) ideas, we suggest that the normal faults Adobe exposed within the Volcanic Tableland extend- Hills ing northward into the southern part of Adobe releasing Valley, west of the White Mountains fault zone, bend 38.00 CF play a similar role and transfer dextral fault slip 0.3 northward into the Adobe Hills (Figs. 2 and 10). 0.5 Adobe CSF The Volcanic Tableland is characterized by 0.6 releasing Valley Queen east- and west-facing normal faults, with an bend average strike of N10–20W (Pinter, 1995), Valley QVF

that cut the 758.9 ± 1.8 ka Bishop Tuff (Sarna- Benton Range Wojcicki et al., 2000). These faults strike ~25°– 35° clockwise relative to motion of the Sierra Nevada microplate with respect to a ﬁ xed North 0.6 restraining American plate (Dixon et al., 2000), thus deﬁ n- bend ing a releasing step. Locally within the Volcanic 37.75

Tableland, normal faults curve westward, deﬁ n- White Mountains releasing ing zones of en echelon faults that trend ~315°, bend subparallel to the Sierra Nevada–North Ameri- can motion. This geometric conﬁ guration suggests that these faults accommodate dextral slip. The normal faults extend northward and east of the Long Valley Caldera into the Benton Range, Black Mountain, and the southern part of Adobe Valley (Krauskopf and Bateman, 1977; Rinehart Volcanic and Ross, 1957; Crowder and Sheridan, 1972; 37.50 WMFZ Bateman, 1965; Nevin, 1963) (Figs. 2 and 10). Tableland Pinter (1995) estimated 144–332 m of Pleisto- cene horizontal extension across the southern part of the Volcanic Tableland; this estimate combined with the age of the Bishop Tuff yields 0.2–0.4 mm/yr of ~N75°E–S75°W exten- Bishop sion since its eruption. Nevin (1963) estimated ~1.94 km of horizontal extension to the north, releasing 25 km across the southern part of Adobe Valley includ- N bend ing Black Mountain and the Benton Range; 37.25

here, north-northwest–striking normal faults OVF cut Pliocene basalt fl ows that can be traced con- tinuously into the Adobe Hills (Krauskopf and Bateman, 1977). This map relation suggests that the basalt fl ows exposed in the Black Mountain and the Benton Range are probably the same age as the ones we dated. Combining that age range with the magnitude of horizontal exten- Figure 10. Simplifi ed map highlighting the kinematic link between the Owens Valley fault sion yields ~0.6 mm/yr of approximately east- and sinistral faults in the Adobe Hills. Map shows faults from the Bishop region northward northeast–west-southwest extension across the to the Adobe Hills, where each major fault or fault zone is shown as a single fault (cf. fault southern part of Adobe Valley. maps in Figs. 2 and 7). Large arrow indicates motion of the Sierra Nevada microplate (SN) The simple fault map in Figure 10 illus- with respect to a fi xed North American plate (NA) (Dixon et al., 2000). Colored arrows with trates how normal faults straddling the south- adjacent numbers indicate fault slip vectors and slip rate (in mm/yr). Red arrows show ern part of Adobe Valley that accommodate the calculated 0.6 mm/yr approximately east–west extension across the southern part of approximately east-west extension transfer slip Adobe Valley (Benton Range and Black Mountain). Blue arrows and adjacent slip rates onto the sinistral faults we have documented. indicate the partitioning of the 0.6 mm/yr vector into parallel and perpendicular vectors These north-northwest–striking normal faults along northwest-striking oblique-slip faults in the eastern Adobe Valley and northeast-strik- accommodated ~0.6 mm/yr of east-northeast– ing sinistral faults in the Adobe Hills. See text for discussion. Solid ball is on the hanging west-southwest extension since the Pliocene. wall of normal faults, and paired arrows indicate relative motion across strike-slip faults. This slip was transferred to northwest-striking CF—Coaldale fault; CSF—Coyote Springs fault; OVF—Owens Valley fault; QVF—Queen oblique-slip faults that bound the eastern margin Valley fault; WMFZ—White Mountains fault zone.

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of Adobe Valley and are likely in the valley, northern end of the Owens Valley fault north- tains fault zone (Frankel et al., 2007; Kirby although the latter are now mostly buried . Based ward to Bishop indicate that dextral slip along et al., 2006; Lee et al., 2009b), or (2) this part on the geometric relationships, slip along this the Owens Valley fault is transferred to both the of the ECSZ underwent a strain transient, as northwest-striking fault system is predicted to White Mountains fault zone (Reheis and Dixon, has been observed in the Mojave Desert (Rock- be oblique, dominantly normal (~0.5 mm/yr), 1996; Kirby et al., 2006, 2008; Sheehan, 2007) well et al., 2000; Peltzer et al., 2001; Oskin and with a lesser component of dextral slip (~0.3 and the Volcanic Tableland. Releasing steps are Iriondo, 2004; Oskin et al., 2007). As described mm/yr). The normal component is nearly par- common elsewhere within the dextral ECSZ- in the following, we propose that additional dex- allel to the sinistral faults we mapped in the WLB, and have been described across the tral slip on faults both to the west and east of Adobe Hills, thus predicting ~0.5–0.6 mm/yr of Towne Pass, Deep Springs, and Queen Valley the Fish Lake Valley and White Mountains fault sinistral slip in the Adobe Hills since the Plio- normal faults and the Death Valley, Panamint zones may account for the apparent discrepancy, cene, consistent with our preferred minimum Valley, and Saline Valley pull-apart basins (Lee although dextral slip rates along many of these sinistral slip rate of 0.4–0.5 mm/yr. The dextral et al., 2001, 2009a, 2009b; Oswald and Wes- faults have not yet been determined. component is almost perpendicular to the sinis- nousky, 2002; Stockli et al., 2000; Burchfi el West of the White Mountains fault zone, tral faults in the Adobe Hills, thus our simple et al., 1987; Burchfi el and Stewart, 1966). Fault normal faults across the Volcanic Tableland kinematic model predicts ~0.2 mm/yr of exten- slip transfer via releasing bends or extensional extending into the southern part of Adobe Valley sion across the sinistral faults. However, there stepovers is also common, at a range of scales, account for some of the discrepancy (Fig. 10). is little, if any, extension accommodated along within strike-slip fault systems worldwide (e.g., To our knowledge, Bateman (1965) was the fi rst these faults. We suggest that the predicted 0.2 Cunningham and Mann, 2007) and has been to suggest that the en echelon geometry of faults mm/yr northwest-southeast extensional com- documented in analog models (e.g., McClay across the Tableland and axes of warping (adja- ponent of slip was partitioned onto the approxi- and Dooley, 1995). Therefore, we are not sur- cent broad anticlines and synclines) were the mately north-south–striking normal faults that prised that a set of releasing steps, of varying result of a “rotational couple” or dextral shear. have been documented throughout this region scales, occur within the northern ECSZ and Moreover, most of the approximately north- by our work and in the far western Adobe Hills transfer slip from one major structure or set of south–striking normal faults strike clockwise (Reheis et al., 2002) as well as onto the north- structures to another. with respect to Sierra Nevada–North America west-striking dextral faults we documented. motion, thus defi ning releasing steps in a dex- The Pliocene east-northeast–west-southwest Regional Tectonics tral shear zone (e.g., Unruh et al., 2003), and a horizontal extensional rate across the Black few of these normal faults curve into parallel- Mountain and Benton Range could be closer to Geologic versus Geodetic Rates ism with Sierra Nevada–North America motion, 0.4 mm/yr, the calculated east-northeast–west- The results from our studies in the Adobe suggesting that slip along these segments is southwest horizontal extensional rate across Hills provide insight into whether there is an dominantly dextral. Others (e.g., Pinter, 1995; southern Volcanic Tableland if (1) the basalt apparent discrepancy between summed geo- Phillips and Majkowski, 2011) attributed the flows exposed in the Black Mountain and logic slip rates versus geodetic rates across the development of normal faults across the Vol- the Benton Range are somewhat older than the northern ECSZ (cf. Lee et al., 2009a; Frankel canic Tableland to the formation of an arch and fl ows we studied in the Adobe Hills, (2) all of et al., 2007; Kirby et al., 2006; Bennett et al., fl exure of the Bishop Tuff. It is possible that the Pleistocene east-northeast–west-southwest 2003) and, combined with the results of sev- faults exposed across the Volcanic Tableland horizontal extension across the southern part of eral other studies along the eastern side Sierra developed as a consequence of both processes the Volcanic Tableland was transferred to nor- Nevada, the forces that drive deformation along that acted broadly simultaneously. Phillips and mal faults exposed in the Black Mountain and the western boundary of the Basin and Range Majkowski (2011) documented a component of Benton Range, and (3) fault slip rates have been Province. At lat ~36.5°N, cumulative long-term dextral slip, in addition to normal slip, farther constant through time. Using the same geo metric geologic dextral slip rates across the Owens west, along the northern Round Valley fault, relationships described here, the implications Valley, Hunter Mountain, northern Death Val- although a dextral slip rate was not determined. for slip rates in the Adobe Hills for a 0.4 mm/yr ley, and State Line faults yield a net dextral slip The dextral slip here projects northward into the horizontal extension rate across Black Moun- rate that is the same, within error, as geodetic Long Valley Caldera. There may be other faults tain and the Benton Range are 0.3–0.4 mm/yr estimates (cf. Lee et al., 2009a; Bennett et al., throughout this region that also accommodate a of extension and 0.1–0.2 mm/yr of dextral slip 2003). In contrast, at lat ~37.5°N there is an component of northwest dextral shear. along the northwest-striking oblique slip faults apparent discrepancy between the summed late Frankel et al. (2007) suggested that dextral in the eastern part of Adobe Valley and 0.3–0.4 Pleistocene dextral geologic slip rates along the shear east of the Fish Lake Valley fault zone mm/yr of sinistral slip and 0.1–0.2 of extension Fish Lake Valley and White Mountains dextral was accommodated via an extensional step- across the northeast-striking sinistral faults in fault zones (Frankel et al., 2007; Kirby et al., over through the Silver Peak–Lone Mountain the Adobe Hills. We suggest that the predicted 2006), which at 2.4–3.9 mm/yr (Frankel et al., extensional complex (Oldow et al., 1994; Hoeft 0.1–0.2 mm/yr northwest-southeast extensional 2007) is less than geodetic rates, assuming that and Frankel, 2010) and vertical axis rotation component of slip across the northeast-striking the geodetic dextral strain rates for the northern (Petronis et al., 2002, 2007). sinistral faults was partitioned onto the approxi- ECSZ at lat ~36.5°N (9.3 ± 0.2 mm/yr) (Bennett mately north-south–striking normal faults and et al., 2003) and central WLB at lat 38°–39°N Geodynamic Implications northwest-striking dextral faults exposed in the (~10 mm/yr) (Hammond and Thatcher, 2007) Major fault slip across the Adobe Hills Adobe Hills region. are the same as at lat 37.5°N. This apparent occurred after the eruption of a sequence of Figures 2 and 10 show a series of releasing discrepancy suggests that either (1) additional 3.43–3.13 Ma basalt fl ows. Early to late Plio- steps between the dextral Owens Valley fault dextral slip was accommodated on structures cene initiation of fault slip or renewed fault and faults bounding the eastern edge of Adobe to the east of these two faults, distributed across slip occurred throughout the western ECSZ- Valley. The set of releasing steps from the Owens Valley, and/or west of the White Moun- WLB–western Basin and Range between lat

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~40°N and 36°N, including (1) dextral slip into the western Mina defl ection (Lee et al., Burchfi el, B.C., and Stewart, J.H., 1966, “Pull-apart” ori- across the northern WLB (Henry et al., 2007); 2009a). We propose that a component of dextral gin of the central segment of Death Valley, Califor- nia: Geological Society of America Bulletin, v. 77, (2) extension across normal faults exposed slip along the Owens Valley fault is transferred p. 439–442, doi:10.1130/0016-7606(1966)77[439: along the eastern fl ank of the central Sierra into the Adobe Hills via dominantly normal, POOTCS]2.0.CO;2. Burchfi el, B.C., Hodges, K.V., and Royden, L.H., 1987, Nevada (Henry and Perkins, 2001), the Tahoe- and to a lesser extent dextral, faults exposed Geology of Panamint Valley–Saline Valley pull-apart Truckee half-graben (Surpless et al., 2002), and across the Volcanic Tablelands, Benton Range, system, California: Palinspastic evidence for low-angle the Wassuk Range front fault (Stockli et al., and southern Adobe Valley. The kinematics of geometry of a Neogene range-bounding fault: Journal of Geophysical Research, v. 92, p. 10,422–10,426, 2002); (3) sinistral slip along the Coaldale fault fault slip transfer into the Adobe Hills occur via doi:10.1029/JB092iB10p10422. located east of the Adobe Hills (Bradley, 2005; a series of releasing bends in a zone dominated Cashman, P.H., and Fontaine, S.A., 2000, Strain partition- Lee et al., 2006); (4) extension across the Queen by dextral slip. This zone of dextral shear west ing in the northern Walker Lane, western Nevada and northeastern California: Tectonophysics, v. 326, Valley fault, and by fault slip transfer, dextral of the White Mountains and Fish Lake Valley p. 111–130, doi:10.1016/S0040-1951(00)00149-9. slip along the Owens Valley–White Mountains fault zones, along with other structures to the Casteel, J.C., 2005, Late Miocene to Holocene faulting along the southwestern Inyo Mountains fault zone, fault zone (Stockli et al., 2000, 2003); (5) exten- west and east of these fault zones, may account eastern California [M.S. thesis]: Ellensburg, Washing- sion across the eastern Inyo fault zone (Lee for the apparent discrepancy between summed ton, Central Washington University, 72 p. et al., 2009a), Saline Range and Dry Mountains long-term geologic dextral slip rates and geo- Crowder, D.F., and Sheridan, M.F., 1972, Geologic map of the White Mountain peak quadrangle, Mono County, (Sternlof, 1988), and Malpais Mesa (Casteel, detic strain rates across the northernmost part California: U.S. Geological Survey Map GQ-1012, 2005); (6) dextral slip along the Hunter Moun- of ECSZ. The fault history we documented in scale 1:62,500. tain fault (Lee et al., 2009a; Burchfi el et al., the Adobe Hills is part of a regionally extensive Cunningham, W.D., and Mann, P., eds., 2007, Tectonics of strike-slip restraining and releasing bends: Geological 1987; Sternlof, 1988); and (7) transtension in early to late Pliocene onset or renewed defor- Society of London Special Publication 290, 482 p., the Coso geothermal fi eld (Monastero et al., mation episode within the western Basin and doi:10.1144/SP290. dePolo, C.M., Peppin, W.A., and Johnson, P.A., 1993, 2005). A change in plate boundary motion has Range. Deformation of this age extends from Contemporary tectonics, seismicity, and potential not been documented for the Pliocene (Atwater the northern WLB (~40°N) southward to the earthquake sources in the White Mountains seis- and Stock, 1998), so plate boundary forces do northern ECSZ (~36°N), and is not associated mic gap, west-central Nevada and east-central Cali- fornia, USA: Tectonophysics, v. 225, p. 271–299, not appear to have been the trigger for the Plio- with changes in plate motion, but coincides doi:10.1016/0040-1951(93)90302-Z. cene initiation of fault slip and renewal of fault with the estimated timing of lithospheric drip Dilles, J., and Gans, P.B., 1995, The chronology of Cenozoic slip within the western ECSZ-WLB and west- from beneath the Sierra Nevada. This temporal volcanism and deformation in the Yerington area, western Basin and Range and Walker Lane: Geological Soci- ern margin of the Basin and Range Province. and spatial relationship suggests that the Plio- ety of America Bulletin, v. 107, p. 474–486, doi:10.1130 The trigger for this deformation episode may cene deformation episode was driven by locally /0016-7606(1995)107<0474:TCOCVA>2.3.CO;2. Dixon, T.H., Robaudo, S., Lee, J., and Reheis, M.C., 1995, have been locally derived internal forces (gravi- derived internal forces. Constraints on present-day Basin and Range deforma- tational potential energy) as a consequence tion from space geodesy: Tectonics, v. 14, p. 755–772, of removal of lithosphere beneath the Sierra ACKNOWLEDGMENTS doi:10.1029/95TC00931. Dixon, T.H., Miller, M., Farina, F., Wang, H., and Johnson, Nevada ca. 3.5 Ma (e.g., Frassetto et al., 2011; We thank Seth Pemble and Josh Stodola for their D., 2000, Present-day motion of the Sierra Nevada block and some tectonic implications for the Basin and Jones et al., 2004; Saleeby et al., 2003; Manley assistance and enthusiasm in the fi eld, and Chris et al., 2000; Ducea and Saleeby, 1998, 1996) Range province, North American Cordillera: Tectonics, Henry for discussions about the fi eld relations in the v. 19, p. 1–24, doi:10.1029/1998TC001088. if delamination extends northward beyond the Adobe Hills. This research was supported by a U.S. Dokka, R.K., and Travis, C.J., 1990, Late Cenozoic strike- southern Sierra Nevada (cf. Zandt et al., 2004; Geological Survey National Cooperative Geologic slip faulting in the Mojave Desert, California: Tec tonics, Frassetto et al., 2011; Hammond et al., 2012). Mapping Program Award (08HQG0055) and a Central v. 9, p. 311–340, doi:10.1029/TC009i002p00311. Washington University Seed Grant to Lee. Nagorsen- Ducea, M.N., and Saleeby, J.B., 1996, Buoyancy sources for Rinke received additional funding from the Univer- a large, unrooted mountain range, the Sierra Nevada, CONCLUSIONS sity of California White Mountain Research Station California: Evidence from xenoliths thermobarometry: Journal of Geophysical Research, v. 101, p. 8229– Graduate Student Mini-grant Program, Central Wash- 8244, doi:10.1029/95JB03452. New geologic map and structural and ington University Graduate Studies and Research, Ducea, M.N., and Saleeby, J.B., 1998, A case for delami- and a Geological Society of America Graduate Stu- 40Ar/39Ar geochronologic data from the Adobe nation of the deep batholithic crust beneath the Sierra dent Research Grant. Thoughtful and constructive Nevada, California: International Geology Review, Hills, western Mina defl ection, highlight a his- reviews from N. Niemi and J. Wakabayashi resulted in v. 40, p. 78–93, doi:10.1080/00206819809465199. tory of pre-Pliocene deformation, rapid basalt an improved manuscript. The views and conclusions Frankel, K.L., Dolan, J.F., Finkel, R.C., Owen, L.A., and fl ow emplacement during the late Pliocene, contained in this document are those of the authors Hoeft, J.S., 2007, Spatial variations in slip rate along and should not be interpreted as necessarily represent- the Death Valley–Fish Lake Valley fault system deter- development of north-northwest–striking nor- mined from LiDAR topographic data and cosmogenic ing the offi cial policies, either expressed or implied, of 10 mal, northwest-striking dextral, and northeast- Be geochronology: Geophysical Research Letters, the U.S. Government. v. 34, L18303, doi:10.1029/2007GL030549. striking sinistral faults within a relatively short Frassetto, A.M., Zandt, G., Gilbert, H., Owens, T.J., and Jones, period of time, and a minimum late Pliocene REFERENCES CITED C.H., 2011, Structure of the Sierra Nevada from receiver sinistral slip rate of ~0.4–0.5 mm/yr. 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