1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Rates of extension along the Fish Lake Valley fault and transtensional deformation in the eastern California shear zone - Walker Lane 24 The oblique-slip normal-dextral Fish Lake Valley fault (FLVF) accommodates the Plamen N. Ganev1,* James F. Dolan1 Kurt L. Frankel2 Robert C. Finkel3, 4 1 Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 3 Department of Earth and Planetary Science, University of California- Berkeley, Berkeley, CA 94720 4 Centre Européen de Recherche et d’Enselignement des Géosciences de l’Environnement (CEREGE), 13545 Aix en Provence, France 2 *corresponding author: Plamen N. Ganev, 3651 Trousdale Parkway, Los Angeles, CA 90089. ganev@usc.edu, 213.740.8208 Keywords: neotectonics, eastern California shear zone, Fish Lake Valley fault, normal fault, geochronology ABSTRACT 25 majority of Pacific-North America plate boundary deformation east of the San Andreas fault in 26 the northern part of eastern California shear zone (ECSZ). New slip rates for the extensional 27 component of the fault determined with LiDAR topographic data and 10Be geochronology of 28 offset alluvial fans at Furnace Creek, Wildhorse Creek, Perry Aiken Creek, and Indian Creek 29 indicate a northward increase in extension rate along the FLVF. Previous studies report 30 cosmogenic 10Be ages of ~94 ka of the Furnace Creek alluvial fan and ~71 ka of the Indian 31 Creek fan. New 10Be dates on from boulders at Wildhorse Creek and Perry Aiken Creek provide 32 surface exposure ages of ~121 ka and ~71 ka, respectively. Assuming a 60º dip for the faults, the 33 cumulative horizontal components of slip measured from the LiDAR data are 8.3 ± 0.4 m at 34 Furnace Creek, 21.5 ± 1.1 m at Wildhorse Creek, 49.1 ± 2.5 m at Perry Aiken Creek, and 43.7 ± Ganev et al., 2009 Page 1 35 2.1 m at Indian Creek. These yield calculated late Pleistocene-Holocene horizontal extension 36 rates of 0.1, 0.2, 0.7, and 0.6 mm/yr, respectively. Comparison of these rates with geodetic 37 measurements of ~1 mm/yr of east-west extension across the northern ECSZ indicates that 38 approximately half of the regional extension is accommodated by the FLVF. When summed with 39 rates of extension on the White Mountains fault and Sierra Nevada frontal fault system, these 40 data suggest that long-term geologic rates of deformation are commensurate with the short-term 41 geodetic extension rate. The northward increase in Pleistocene extension rates is opposite the 42 trend of the dextral slip rate along the FLVF, likey reflecting an extensional transfer zone in 43 northern Fish Lake Valley that relays strain to the northeast across the Mina Deflection and into 44 the Walker Lane. 45 46 47 INTRODUCTION The eastern California shear zone (ECSZ)- Walker Lane is an evolving fault system east 48 of the San Andreas fault that accommodates ~20-25% (9-10 mm/yr) of Pacific-North America 49 plate boundary deformation (e.g., Bennett et al., 2003; Dixon et al., 2000, 2003; Dokka and 50 Travis, 1990; Faulds et al., 2005; Hearn and Humphreys, 1998; Humphreys and Weldon, 1994; 51 McClusky et al., 2001; Miller et al., 2001; Thatcher et al., 1999; Wesnousky, 2005; Frankel et 52 al., 2007a). The ECSZ is ~500 km long and extends northward from the San Andreas fault 53 through the Mojave Desert, and along the east side of the Sierra Nevada. In the Mojave section 54 of the ECSZ, fault motion is almost entirely right-lateral and slip is localized along several major 55 north-northwest-striking faults (Oskin et al., 2008). North of the active left-lateral Garlock fault, 56 motion is accommodated on four major fault systems: the Owens Valley, Panamint Valley- 57 Saline Valley-Hunter Mountain, Death Valley-Fish Lake Valley, and Stateline fault zones (Fig. Ganev et al., 2009 Page 2 58 1; e.g., Frankel et al., 2008). In the northern part of the ECSZ, between latitude 37ºN and 38ºN, 59 dextral motion between the stable Sierra Nevada block and North America is distributed from 60 Long Valley Caldera in the west to the Silver Peak-Lone Mountain extensional complex in the 61 east, with ~35% of the dextral shear being accommodated by the White Mountains and Fish 62 Lake Valley faults (Kirby et al., 2006; Frankel et al., 2007a, b). Multiple northeast-striking, 63 down-to-the-northwest normal faults transfer slip between the right-lateral Owens, Panamint 64 Valley-Saline Valley-Hunter Mountain, and Death Valley-Fish Lake Valley fault systems (e.g., 65 Reheis and Dixon , 1996). North of the Mina deflection, strain is accommodated by a series of 66 right-lateral faults as part of the Walker Lane belt (Wesnousky, 2005a, b). 67 Although dextral shear accommodates most slip on the northwest-striking faults in Fish 68 Lake Valley, fault segments that strike approximately north exhibit a relatively large extensional 69 component of slip. Space-based geodetic studies demonstrate that the current strain field is 70 consistent with transtensional deformation and indicate an extension rate of ~1 mm/yr measured 71 normal to the predominant ~ N25ºW strike of the ECSZ at this latitude (e.g., Bennett et al. 2003; 72 Savage et al., 2001; Wesnousky, 2005a). This geodetically-derived extension rate in the northern 73 ECSZ is most likely distributed among the Sierra Nevada frontal fault, the Volcanic Tablelands, 74 the White Mountains fault, and the Fish Lake Valley fault system (Fig. 1). The geologically- 75 derived extension rates on the Sierra Nevada frontal fault (Le et al., 2006) and the White 76 Mountains fault (Kirby et al., 2006) are both ~0.2 mm/yr. Therefore, if the geodetic and geologic 77 rates of deformation are equal and the extensional component of the strain can be accounted for 78 on recognizable faults, the FLVF must accommodate as much as half of the extensional 79 deformation within the northern ECSZ. Ganev et al., 2009 Page 3 80 In this paper, we report new observations from our analysis of light detection and ranging 81 (LiDAR) data, as well as terrestrial cosmogenic nuclide (TCN) dating of faulted land forms 82 along the Fish Lake Valley fault. Our results provide new, geochronologically- determined, late 83 Pleistocene-Holocene extension rates on this fault system that bear on how motion in the ECSZ 84 is accommodated, and ultimately transferred northward to the Walker Lane. 85 86 DEATH VALLEY-FISH LAKE VALLEY FAULT ZONE 87 The Fish Lake Valley fault, which forms the northern 80 km of the Death Valley-Fish 88 Lake Valley fault system, is marked by steep, east-facing fault scarps, ponded drainages, and 89 shutter ridges indicative of recent fault activity (Brogan et al., 1991; Reheis, 1992; Reheis et al., 90 1993; Reheis et al., 1995; Frankel et al., 2007a, b). The southern and central sections of the 91 FLVF strike predominantly northwest, whereas the northern part of the fault is characterized by 92 numerous north-striking strands that splay out into Fish Lake Valley from the main range- 93 bounding fault (Fig. 2; Sawyer, 1991; Reheis and Sawyer, 1997) . 94 Based on differences in fault strike and fault scarp morphology, Brogan et al. (1991) and 95 Sawyer (1990, 1991) separated the FLVF into four sections. From south to north these are the 96 Cucomongo Canyon, Oasis, Dyer, and Chiatovitch Creek sectons. Right-lateral motion on the 97 Fish Lake Valley fault is thought to have begun ~10 Ma ago (Reheis and Sawyer, 1997), and the 98 strike-slip rate averaged over late Pleistocene-Holocene time is 2.5 to 3 mm/yr (Frankel et al., 99 2007b). The extensional component of oblique normal-dextral motion, responsible for the 100 opening of Fish Lake Valley, most likely began ~ 5 Ma ago, as suggested by the observations 101 that the bounding faults in the northern section of the valley cut across sedimentary rocks of the 102 Miocene Esmeralda basin (Reheis and Sawyer, 1997). On the west side of the White Mountains, Ganev et al., 2009 Page 4 103 the right-lateral White Mountains fault originated later, at ~3 Ma (Stockli et al., 2003); the late 104 Pleistocene-Holocene White Mountains fault oblique-slip rate is ~0.9 mm/yr parallel to a net 105 slip vector plunging ~20° toward 340°-350° (Kirby et al., 2006). 106 The focus areas of our study are normal fault scarps formed in four alluvial fans along 107 the Chiatovich Creek, Dyer, and Oasis sections of the fault, which have been extensively mapped 108 by a number of researchers (Fig. 2; Brogan et al., 1991; Reheis, 1992; Reheis et al., 1993 and 109 1995). These four alluvial fans are deposited along the eastern White Mountains piedmont at the 110 mouths of (from south to north) Furnace Creek, Wildhorse Creek, Perry Aiken Creek, and Indian 111 Creek. We refer to each of our study sites relative to the respective creek that formed them. At 112 two of the sites, Furnace Creek and Indian Creek, the fault zone exhibits predominantly right- 113 lateral strike slip, with large (180-290 m) dextral offsets. Using cosmogenic 10Be surface 114 exposure geochronology, Frankel et al. (2007b) determined the ages of the offset surfaces (unit 115 Qfi of Reheis et al., 19XX) to be ~94 ka for Furnace Creek and ~71 ka for Indian Creek; the 116 resulting right-lateral strike-slip rates at these two locations are 3.1 ± 0.4 mm and 2.5 ± 0.4 117 mm/yr, respectively. Multiple normal-fault scarps are also present in both of these alluvial fans, 118 as we discuss below. 119 Our other two study sites, Wildhorse Creek and Perry Aiken Creek, are located between 120 the Furnace Creek and Indian Creek fans (Fig. 1). Both the Wildhorse Creek and Perry Aiken 121 Creek sites have numerous fault scarps cutting the alluvium with a predominantly normal 122 component of slip. The highest single normal-fault scarp (minimum vertical displacement of ~85 123 m) along the entire Death Valley-Fish Lake Valley fault zone is found just north of Perry Aiken 124 Creek (Reheis and Sawyer, 1997). Reheis (1993) used tephrochronology to suggest that alluvial Ganev et al., 2009 Page 5 125 fans at Wildhorse Creek and Perry Aiken Creek were deposited during middle to late Pleistocene 126 time. 127 GEOMORPHIC ANALYSIS OF NORMAL FAULT SCARPS 128 The analysis of LiDAR digital topographic data is an integral component of our study. 129 The LiDAR data were collected in the Fall of 2005 by the National Center for Airborne Laser 130 Mapping (NCALM) using an Optech Inc. Model ALTM 2033 laser mapping system. The laser 131 was installed on a Cessna 337 twin engine aircraft, which flew over the fault trace at an average 132 elevation of 600 m above ground level and an average speed of 60 m/s. The pulse rate frequency 133 of the Optech ALTM 2033 was set at 33 KHz and it recorded the first and last returns of each 134 pulse, plus the relative intensity of each return. The average shot density for the LiDAR data was 135 ~3 points/m2. The aircraft was equipped with a dual-frequency GPS receiver and a real-time 136 display of the flight path and area coverage. High-resolution digital elevation models (DEMs) 137 with 5-10 cm vertical accuracy and 1 m horizontal resolution were produced using a kriging 138 algorithm in SURFER software (Version 8.04; Carter et al., 2007; Sartori, 2005). 139 ArcGIS (Version 9.2) was used to produce hill-shaded relief maps to aid in the 140 identification and mapping of all normal fault scarps at each site. We analyzed a total of 27 141 profiles perpendicular to the strike of each set of scarps and measured the mean vertical 142 component of displacement (Figs. 3-7, Table 1; please also see Data Repository item 1). The 143 profiles were collected across fault scarps formed in unconsolidated alluvium where material is 144 transported down-scarp by rain splash and gravity-driven soil creep; it is assumed that material is 145 not transported in or out of the profile (e.g., Hanks et al., 1984; McCalpin, 1996; Arrowsmith et 146 al., 1998). Maximum vertical components of displacement of the alluvial surfaces were 147 calculated geometrically using the middle of the fault scarp (Fig. 8; Hanks et al., 1984). The Ganev et al., 2009 Page 6 148 horizontal component of each displacement was subsequently calculated using simple 149 trigonometric relationships by assuming a 60º dip of the fault plane for each scarp (e.g., Kirby et 150 al., 2006; Le et al., 2007; Lee et al., 2009). Uncertainties associated with measurements of the 151 vertical components of each displacement include surface roughness (~20 cm) and the vertical 152 accuracy (~10 cm) of the LiDAR data (e.g., Le et al., 2006). Combined, these two uncertainties 153 are <5% of the total mean vertical component of displacement at each site and thus we report a 154 conservative displacement error of 5%. We report the horizontal (extensional) component of 155 displacement across the fault zone at each of the four sites, rather than the total vertical 156 separation, due to the presence of multiple scarps associated with antithetic faults, which would 157 lead to a reduction in the net vertical displacement across the fault zone; we feel that the total 158 extension represents a more robust measure of the net fault slip. 159 160 161 Furnace Creek Two fault sets are prominent at the Furnace Creek site: north-northwest trending faults of 162 the main, predominantly right-lateral strand of the FLVF, and a northeast-trending set of 163 distributed normal faults to the east (Fig. 3A). The northeast-trending set of distributed faults 164 accommodate slip that is not directly related to the extension on the FLVF, and we therefore 165 analyzed eight profiles across the scarps of the main, predominantly right-lateral fault strand at 166 the Furnace Creek site (Figs. 3A and 4). Transects PP’-P1P1’ and QQ’-Q1Q1’ are superimposed in 167 order to capture the vertical component of displacement across the right-laterally offset alluvial 168 fan. Inasmuch as right-lateral offset of the alluvial fan at this location will result in an apparently 169 smaller scarp height, these profiles provide us with the minimum vertical displacement. Profiles 170 RR’ through WW’ also record the vertical component of fault offset across a strand with Ganev et al., 2009 Page 7 171 predominantly right-lateral slip, and therefore the cumulative mean horizontal displacement 172 measured at Furnace Creek is 8.3 ± 0.4 m (Fig. X). 173 174 175 Wildhorse Creek The two profiles (NN’ and OO’) we analyzed at Wild Horse Creek were oriented to most 176 effectively capture all five of the main identifiable fault scarps (Figs. 3B and 5). Although some 177 of the scarps face east and others face west, which would lead to a reduction in the net vertical 178 displacement across the fault zone, it does not affect our calculations in terms of horizontal 179 displacement. Although there is evidence for right-lateral slip at this site (e.g., the shutter ridge to 180 the south of the active channel) no measurable offset markers are present. The cumulative mean 181 horizontal displacement at Wildhorse Creek is 19.9 ± 1.0 m (Fig. X). 182 183 184 Perry Aiken Creek We used four transects, JJ’ through MM’, to measure the cumulative displacement at the 185 Perry Aiken Creek site (Figs. 3C and 6). The vertical component of total displacement (85m) at 186 this site is in agreement with previous measurements by Reheis and Sawyer (1997), who 187 suggested ~85 m. Similar to the Wildhorse Creek site, although evidence for right-lateral 188 component of slip is recognizable (e.g., the deflected canyon and abandoned channel at alluvial 189 fan head), no measurable dextral offset markers are present. The cumulative mean horizontal 190 component of displacement at Perry Aiken Creek is 49.1 ± 2.5 m. 191 192 Indian Creek Ganev et al., 2009 Page 8 193 At the Indian Creek site we analyzed nine topographic profiles across three different sets 194 of fault scarps (Figs. 3D and 7). Profile AA’ extends across the two normal-fault scarps, one 195 facing east and one facing west, to the west of the range-front dextral fault strand. We used 196 profile BB’ to capture the horizontal displacement across the main right-lateral strand of the 197 fault. Profiles CC’ through II’ were used to measure the displacement across a set of distributed, 198 north-northeast-trending normal faults to the east. The vertical displacement (~75 m) at this site 199 is larger than the previously reported preferred vertical component of displacement of 40 m by 200 Reheis and Sawyer (1997). Our preferred cumulative mean horizontal displacement at Indian 201 Creek is 43.7 ± 2.1 m. 202 203 TERRESTRIAL COSMOGENIC NUCLIDE GEOCHRONOLOGY We used terrestrial cosmogenic nuclide geochronology (TCN) to date the offset alluvial 204 fans along the FLVF. TCN geochronology allows for the determination of the age of 205 abandonment of an alluvial surface (e.g., Gosse and Phillips, 2001). When combined with 206 measured displacements across normal fault scarps, ages of the offset landforms can yield rates 207 of deformation. TCN geochronolgy measures the concentration of nuclides produced in a rock by 208 the interaction between cosmic rays and minerals at the Earth’s surface (e.g., Lal, 1991; Gosse 209 and Phillips, 2001). In order to obtain plausible results, several criteria must be satisfied: (1) the 210 sampled boulder must be in the same geometry as it was at the time of deposition; (2) the 211 sampled boulder should not have prior exposure history (inheritance); and (3) boulders with 212 evidence of erosion should not be sampled since they will provide an attenuated concentration of 213 cosmogenic isotopes and hence, an apparently young age (Gosse and Phillips, 2001). 214 215 The isotope of interest for this study is 10Be, which is produced through spallation and muon-induced reactions with Si and O in quartz. Beryllium-10 is well-retained in quartz minerals Ganev et al., 2009 Page 9 216 which we collected from granitic boulders embedded in the surface of the offset alluvial fans. 217 Fifteen samples were collected from the top 1 to 5 cm of large granitic boulders (Table 1). These 218 boulders came from the stable parts of fan surfaces mapped by Reheis et al. (1993, 1995) as Qfm 219 at Wildhorse Creek and Qfi at Perry Aiken Creek (Fig. 9). We carefully selected well-varnished 220 boulders that lack evidence of erosion (e.g., “sombrero–shaped” boulders). 221 Quartz was purified by standard techniques and Be was extracted using ion-exchange 222 chromatography, precipitated as BeOH, and converted to BeO at the Georgia Institute of 223 Technology cosmogenic nuclide geochronology laboratory (e.g., Kohl and Nishiizumi, 1992; 224 Bierman et al., 2002). The 10Be/9Be ratio for each sample was measured at the Center for 225 Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory and model 10Be 226 ages were calculated using the CRONUS-Earth 10Be-26Al exposure age calculator (version 2.0; 227 http://hess.washington.edu/math) and constant 10Be production rates (Lal, 1991; Stone, 2000; 228 Balco et al., 2008). 229 230 231 Wildhorse Creek Fan Age We analyzed six TCN samples collected from the Qfm alluvial fan surface at Wildhorse 232 Creek. The Qfm surface is characterized by subdued to moderately-incised channels, well- 233 developed desert pavement, and a continuous, thick desert varnish on clasts. Furthermore, Qfm 234 exhibits a thick silty vesicular A horizon, strong argillic B horizon, and stage IV laminar 235 carbonate development (e.g., Reheis and Sawyer, 1997). Samples from this surface range in age 236 from 100 ± 9 ka to 139 ± 13 ka, forming a tight cluster at ~120 ka (Fig. 10A). The mean age and 237 standard deviation of these dates is 121 ± 14 ka. We take the clustered distribution of these Ganev et al., 2009 Page 10 238 samples as evidence that the Qfm surface has remained relatively stable since the time of 239 deposition and that inheritance is minimal. 240 241 242 Perry Aiken Creek Fan Age Nine TCN samples were analyzed from the Qfi alluvial fan surface at Perry Aiken Creek. 243 The Qfi surface is characterized by subdued to moderately-incised channels, well-developed 244 desert pavement, and a continuous, thick desert varnish on clasts. In addition, Qfi is 245 distinguished by a well-developed soil with a 5-to-10-cm-thick silty vesicular A horizon, a weak 246 argillic B horizon with thin clay films and a stage II to III carbonate development (e.g., Reheis 247 and Sawyer, 1997). Our Qfi ages, like the ages from Wildhorse Creek, exhibit a pronounced, 248 single peak distribution with a mean age and standard deviation of 71± 8 ka (Fig. 10B). The 249 range of ages varies from 54 ± 5 ka to 79 ± 7 ka. As with the Wildhorse Creek samples, we take 250 the tight cluster of ages as an indication that the Qfi surface has remained relatively stable and 251 that there is negligible inheritance. The age we obtained for Qfi at Perry Aiken Creek is in close 252 agreement with the previously determined 10Be age of 71 ± 8 ka for the Qfi deposit at Indian 253 Creek by Frankel et al. (2007b), and the 50-130 ka age estimated by Reheis and Sawyer (1997) 254 on the basis of soil development and surface morphology. 255 256 257 Furnace Creek and Indian Creek Fan Ages The ages of the alluvial fans at Furnace Creek and Indian Creek were recently determined 258 by Frankel et al. (2007b) using cosmogenic 10Be geochronology, and we utilize their results to 259 determine the extension rates at these two locations. At Furnace Creek, Frankel et al. (2007b) 260 report an age for surface Qfio (modified from Qfi of Reheis and Sawyer, 1997) of 94 ± 11 ka, Ganev et al., 2009 Page 11 261 while at Indian Creek they determined the age of surface Qfiy (modified from Qfi of Reheis and 262 Sawyer, 1997) to be 71 ± 8 ka. Both of these ages are in agreement with previously reported soil 263 and fan morphology data from those sites by Reheis and Sawyer (1997). 264 265 Summary of Rate Data Along the Fish Lake Valley Fault 266 We calculate extension rates at each of our four study sites by combing vertical 267 components of displacement, fan surface ages, and an assumed 60° fault dip. Specifically, our 268 extension rates are computed by combining probability density functions of the measured 269 displacements and TCN ages and employing a Gaussian uncertainty model (e.g., Bird, 2007; 270 McGill et al., 2009; Zechar and Frankel, in review). Uncertainties in the extension rates are 271 reported at the 2σ confidence interval. The resulting east-west extension rates from south to north 272 are: Furnace Creek = 0.1 ± 0.1 mm/yr, Wildhorse Creek = 0.2 ± 0.1 mm/yr, Perry Aiken Creek = 273 0.7 +0.3/-0.1 mm/yr, and Indian Creek = 0.6 +0.2/-0.1 mm/yr. The 10Be dates from all four of 274 our sites should be considered maximum ages for calculating the extension rates because the 275 normal fault scarps must have developed after the deposition and abandonment of the Qfi and 276 Qfm alluvial fan deposits. Moreover, although we are confident that we have captured all of the 277 main fault strands that exhibit a normal component of slip, some distributed deformation that 278 does not manifest itself as generally recognizable fault scarps could be present. Furthermore,, 279 decreasing the assumed dip angle of 60º for the fault planes would also increase the calculated 280 rates of extension. Thus, the combination of the maximum TCN ages, minimum displacements, 281 and the assumed fault dip yield minimum extension rates. 282 283 DISCUSSION Ganev et al., 2009 Page 12 284 The new rate data described above allow us to place constraints on the style and location 285 of strain transfer from faults of the ECSZ to structures in the Walker Lane through the Mina 286 Deflection. The extension rates we obtain on the FLVF increase northward from 0.1 +/- 0.1 287 mm/yr and 0.2 +/- 0.1 mm/yr at Furnace Creek and Wildhorse Creek,, to 0.7 +0.3/-0.1 m/yr and 288 0.6 +0.2/-0.1 mm/yr at the Perry Aiken Creek and Indian Creek. These extension rates are 289 similar to those estimated by Reheis and Sawyer (1997), who reported a preferred late- 290 Pleistocene vertical component of oblique slip at Furnace Creek of 0.3 mm/yr and 0.8 mm/yr at 291 Indian Creek, on the basis of tephrochronology. If we assume a 60º dip for the fault plane, their 292 preferred extension rates at Furnace Creek and Indian Creek are 0.2 mm/yr and 0.5 mm/yr, 293 respectively. No preferred vertical component of total slip rate was reported by Reheis and 294 Sawyer (1997) for Wildhorse Creek and Perry Aiken Creek. 295 296 297 Geodetic vs. Geologic Rates of Extension If the present-day extension rate of ~1 mm/yr determined by GPS (Bennett et al., 2003; 298 Wesnousky, 2005a) has remained constant over Holocene to late Pleistocene timescales at the 299 latitude of Fish Lake Valley, then approximately half of this regional extension must be 300 accommodated by the northern FLVF. The remaining extensional deformation appears to be 301 taken up by faults to the west, including the White Mountains fault (Kirby et al., 2006), 302 distributed normal faulting in the Volcanic Tablelands (Kirby et al., 2006; Greene et al., 2007; 303 data of Greene and Kirby in Frankel et al., 2008a), and the Sierra Nevada frontal fault system (Le 304 et al., 2006), including the Round Valley and Hilton Creek faults north of Owens Valley (Fig. 305 11; Berry et al., 1997) . The oblique-normal-dextral White Mountains fault exhibits a late 306 Pleistocene extension rate at the latitude of our Furnace Creek site of ~0.2 mm/yr (Kirby et al., Ganev et al., 2009 Page 13 307 2006), while at approximately the same latitude there is clear evidence for distributed normal 308 faulting across the Volcanic Tablelands (e.g., Sheehanand Dawers, 2005; Pinter and Keller, 309 1995). Further west at the same latitude Berry (1997) reports a 0.5-0.6 mm/yr late Pleistocene 310 vertical component of slip on the Round Valley fault. This is equivalent to an extension rate on a 311 60° dipping fault of ~0.3 mm/yr. Therefore, by combining all known extension rate data from 312 these faults of the northern ECSZ we can account for nearly all of the geodetically-determined 313 extension deformation at the latitude of central/northern Fish Lake Valley. 314 315 316 Strain Transfer at the ECSZ-Walker Lane Transition Recent work by Frankel et al. (2007b) at Furnace Creek and Indian Creek determined the 317 late-Pleistocene right-lateral slip rate of the FLVF oblique system. The reported slip rates of 3.1 318 ± 0.4 mm/yr at Furnace Creek and 2.5 ± 0.4 mm/yr at Indian Creek, suggest an apparent 319 northward decrease in dextral motion along the FLVF. The northward decrease in right-lateral 320 slip rate is even more pronounced in the northern-most part of Fish Lake Valley, where the 321 surface expression of the fault zone ends abruptly less than ~15 km north of Indian Creek. 322 The observation that extension rates increase northward along the FLVF while dextral 323 rates decrease has important implications for the distribution of strain along this section of the 324 Pacific-North America plate boundary and, more generally, for mechanisms of slip transfer along 325 evolving, structurally complex fault systems (Fig. 11). The FLVF system ends just north of 326 Indian Creek and slip is transferred northeastward across the Mina Deflection onto oblique 327 normal-right-lateral faults of the Walker Lane belt. Thus, the Mina Deflection can be thought of 328 as a major right step (~80 km wide) in a dominant right-lateral fault system (e.g., Oldow et al., 329 1994, 2001; Wesnousky, 2005a; Petronis et al., 2002; Petronis, 2005). Within the Mina Ganev et al., 2009 Page 14 330 Deflection deformation is accommodated by left-lateral faults and clockwise block rotations 331 (Wesnousky, 2005a).In general, both the northward increase in extension that we document, and 332 the northward decrease in dextral slip documented by Frankel et al. (2007b) reflect transfer of 333 slip off the predominantly right-lateral FLVF onto north- and northeast-trending normal faults as 334 part of a distributed zone of slip transfer between the Emigrant Peak fault and the east-west- 335 trending left-lateral faults of the Mina Deflection. For example, the north-northeast-trending 336 normal faults that cut the fan to the east of the main range front fault strands at the Furnace 337 Creek site appear to “pull” slip off the FLVF system and transfer it northeastward onto the 338 Emigrant Peak fault system (Figure ?). Similarly, the north-northeast-trending normal faults at 339 Indian Creek serve to transfer slip off the FLVF and into the zone of distributed normal faulting 340 in this corner of Fish Lake Valley, leaving only 2.5 mm/yr of right-lateral strike-slip motion on 341 the FLVF at this site (Fig. X; Frankel et al., 2007b). This diffuse normal faulting, together with 342 normal displacements on the prominent Emigrant Peak fault system, account for the 343 development of the deep basin that defines the northeast-trending part of northern Fish Lake 344 Valley (including the dry ‘Fish Lake”, proper). However, the most pronounced decrease in right- 345 lateral strike-slip rate along the FLVF occurs just north of the Indian Creek site, where the 346 geomorphic expression of the fault system dies out completely within a zone of extensive recent 347 lava flows inthe Volcanic Hills (Fig. 11). Thus, between the north end of the geomorphically 348 well-defined FLVF at Indian Creek, and the left-lateral faults of the Mina deflection to the north, 349 it appears that distributed down-to-the-northwest normal faulting may accommodate as much as 350 2.5 mm/yr of dextral motion (e.g., Frankel et al., 2007b). The coincidence of this zone of 351 apparent distributed normal faulting and the extensive volcanism in the Volcanic Hills suggests 352 that the volcanism may be localized by this slip transfer zone. Ganev et al., 2009 Page 15 353 Ultimately, at least some of this motion is must be accommodated along the east-west- 354 trending left-lateral faults of the Mina Deflection (Fig. 1; the Coaldale, Excelsior Mountains, and 355 Rattlesnake Flat faults). For example, the Coaldale fault, which has a minimum late Pliocene 356 sinistral slip rate of ~0.3-0.4 mm/yr (Lee et al., 2006) could potentially accommodate some of 357 the east-west extension that we observe in the northern part of Fish Lake Valley. But, the manner 358 in which this slip transfers northward onto the left-lateral faults remains unclear, as the there are 359 no geomorphically well-expressed faults in the 15-km-wide zone between the northern end of the 360 FLVF and the Coaldale fault (Fig. X). If, as we suspect, this slip is transferred northward into the 361 Mina Deflection along a diffuse set of highly distributed normal faults beneath the Volcanic 362 Hills, then this would imply that either clockwise rotations and/or left-lateral slip rates on the 363 Mina Deflection faults would increase to the east. 364 One possibility that we consider is that the northeast-trending normal faults that 365 characterize the northern part of Fish Lake Valley represent an early stage in the evolution of 366 faults similar to the Coaldale fault. In such a scenario, these faults would develop as northeast- 367 trending normal faults that act to transfer strain across the major right step of the Mina 368 Deflection. In response to ongoing right-lateral shear, these northeast-trending normal faults 369 would gradually rotate clockwise into a more east-west orientation, switching to left-lateral 370 strike-slip structures as a result of this reorientation. However, the well-established nature of the 371 northeast-trending basin along the north side of the Silver Peak Range, and long-term activity of 372 the north- to northeast-trending Emigrant Peak fault system (Petronis et al., 2002; Petronis, 2005) 373 argue that these are well-established, long-lived features that do not appear to be actively 374 rotating. In either case , slip transfer across the northern end of Fish Lake Valley into and across 375 the Mina Deflection appears to involve a large component of distributed normal faulting, as well Ganev et al., 2009 Page 16 376 as left-lateral strike-slip faulting, perhaps quite distributed at the northwest corner of the valley, 377 and clockwise rotations (Fig. 12). 378 379 380 CONCLUSIONS New LiDAR topographic data and cosmogenic 10Be geochronology of offset alluvial fan 381 deposits on the dextral-oblique Fish Lake Valley fault yield well-determined late Pleistocene- 382 Holocene extension rates on this major oblique normal-dextral fault system. The surface 383 exposure ages of four sites, Furnace Creek, Wildhorse Creek, Perry Aiken Creek, and Indian 384 Creek (from south to north) range from ~71 ka to ~121 ka, and the mean horizontal extensional 385 components of displacement at these sites range from ~8 m to ~49 m. By combining probability 386 density functions of these displacements and ages, we find that extension rates averaged over late 387 Pleistocene-Holocene time vary from 0.1 mm/yr at Furnace Creek and 0.2 mm/yr at Wildhorse 388 Creek in the south, to 0.7 and 0.6 mm/yr at Perry Aiken Creek and Indian Creek, respectively, to 389 the north. 390 These rate suggest that the FLVF accommodates approximately half of the region-wide 391 geodetic rate of extension. When summed with extension rates along the western White 392 Mountains piedmont, the Sierra Nevada frontal fault, and distributed deformation across the 393 Volcanic Tablelands, the long-term geologic rates of extension are commensurate with the short- 394 term rates determined from GPS data. 395 The increase in the east-west extensional component of slip towards the northern end of 396 the ECSZ reflects a gradual northeastward transfer of slip off the predominantly right-lateral 397 FLVF and across the Mina Deflection as part of a distributed zone of north-east-trending normal 398 faulting. Further north, in the Mina Deflection proper, deformation is accommodated Ganev et al., 2009 Page 17 399 predominantly by the presence of east-west oriented left-lateral faults. Collectively, the 400 distributed normal faulting in northern Fish Lake Valley, together clockwise rotations and 401 motion on the east-west left-lateral faults of the Mina Deflection, serve to transfer deformation 402 through this major right-step in the eastern California shear-zone-Walker Lane belt. 403 404 405 ACKNOWLEDGEMENTS We thank Dylan Rood and Alicia Nobles for assistance with sample preparation and 406 analysis, and Trevor Thomas for his assistance in the field. XXXXXXXXX and XXXXXXXXX 407 provided thoughtful reviews that significantly improved the manuscript. The LiDAR data were 408 collected by the National Center for Airborne Laser Mapping, and we are indebted to Michael 409 Sartori and Ionut Iordache for help with data processing. 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Sartori, M., 2005, ALSM acquisition in Death Valley National Park, Report on Data Processing, National Center for Airborne Laser Mapping, University of Florida, Gainesville, 13 pp. Savage, J.C., Gan, W., and Svarc, J.L., 2001, Strain accumulation and rotation in the eastern California shear zone, Journal of Geophysical Research, 106(B10), 21,995-22,007. Sawyer, T.L., 1990, Quaternary geology and neotectonic activity along the Fish Lake Valley fault zone, Nevada and California, [M.S. Thesis], Reno, University of Nevada, 379 p. Sawyer, T.L., 1991, Late Pleistocene and Holocene paleoseismicity and slip rates of the northern Fish Lake Valley fault zone, Nevada and California, in, Reheis, M.C., ed., Guidebook for field trip to Fish Lake Valley, California-Nevada: Golden, Colorado, Pacific Cell, Friends of the Pleistocene, 114-138. Stockli, D.F., Dumitru, T.A., McWilliams, M.O., and Farley, K.A., 2003, Cenozoic tectonic evolution of the White Mountains, California and Nevada, GSA Bulletin, 115, 788-816, doi: 10.1130/0016-7606(2003)115<0788:CTEOTW>2.0.CO;2. Stone, J.O., 2000, Air pressure and cosmogenic isotope production, Journal of Geophysical Research, 105, 23,753-23,759. Ganev et al., 2009 Page 22 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 Thatcher, W., Foulger, G.R., Julian, B.R., Svarc, J., Quilty, E., and Bawden, G.W., 1999, Present day deformation across the Basin and Range province, western United States, Science, 283, 1714-1718, doi: 10.1126/science.283.5408.1714. Wesnousky, S.G., 2005a, Active Faulting in the Walker Lane, Tectonics, 24, TC3009, doi:10.1029/2004TC001645. Wesnousky, S.G., 2005b, The San Andreas and Walker Lane fault systems, western North America: transpression, transtension, cumulative slip and the structural evolution of a major transform plate boundary, Journal of Structural Geology, 27, 1505-1512. Zechar, J.D., and Frankel, K.L., in review, Incorporating and reporting uncertainties in fault slip rates, Journal of Geophysical Research - Solid Earth.. Figure captions 623 Figure 1: Hillshaded relief map and Quaternary faults in the northern ECSZ. Fish Lake Valley 624 fault is shown in white. The corners of Figure 2 are shown in black. Faults are from the USGS 625 Quaternary fault and fold database. AHF- Ash Hill fault, ALF- Airport Lake fault, BSF- Benton 626 Springs fault, CF- Coaldale fault, EF- Excelsior Mountains fault, EPF- Emigrant Peak fault, 627 EVF- Eureka Valley fault, DSF- Deep Springs fault, FLVF- Fish Lake Valley fault, GF- Garlock 628 fault, HCF- Hilton Creek fault, HMSVF- Hunter Mountain-Saline Valley fault, LMF- Lone 629 Mountain fault, MLF- Mono Lake fault, NDVF- northern Death Valley fault, OVF- Owens 630 Valley fault, PSF- Petrified Springs fault, PVF- Panamint Valley fault, QVF- Queen Valley fault, 631 RF- Rattlesnake Flat fault, RVF- Round Valley fault, SLF-Silver Lake fault, SNF- Sierra Nevada 632 frontal fault, SVF- Saline Valley fault, TMF- Tin Mountain fault, TPF- Towne Pass fault, WF- 633 Warm Springs fault, WMF- White Mountains fault. GPS strain accumulation rates from Bennett 634 et al. (2003). 635 Ganev et al., 2009 Page 23 636 Figure 2: Detailed index map of the study area. The locations of study sites are labeled 1 through 637 4 from south to north: 1- Furnace Creek; 2- Wildhorse Creek; 3- Perry Aiken Creek; 4- Indian 638 Creek. DSF- Deep Springs fault, EPF- Emigrant Peak fault, FLVF- Fish Lake Valley fault, OVF- 639 Owens Valley fault, QVF- Queen Valley fault; WMF- White Mountains fault. 640 641 Figure 3: Selected topographic profiles across alluvial fan surfaces and calculated vertical 642 components of displacement from the four study sites: (a) Furnace Creek; (b) Wildhorse Creek; 643 (c) Perry Aiken Creek; (d) Indian Creek. See Figures 4-7 for profile locations. 644 645 Figure 4: Hillshaded LiDAR-derived DEM of the Furnace Creek site showing the topographic 646 profiles analyzed. The number by each fault scarp corresponds to the fault number in Table 1. 647 The mapped Quaternary surfaces are modified from Reheis et al. (1993). See Table 1 for the 648 detailed measurements of scarp heights. 649 650 Figure 5: Hillshaded LiDAR-derived DEM of the Wildhorse Creek site showing the topographic 651 profiles analyzed. The green dots indicate the locations of the dated samples. The number by 652 each fault scarp corresponds to the fault number in Table 1. The mapped Quaternary surfaces are 653 modified from Reheis et al. (1993). See Table 1 for the detailed measurements of scarp heights. 654 655 Figure 6: Hillshaded LiDAR-derived DEM of the Perry Aiken Creek site showing the 656 topographic profiles analyzed. The green dots indicate the locations of the dated samples. The 657 number by each fault scarp corresponds to the fault number in Table 1. The mapped Quaternary Ganev et al., 2009 Page 24 658 surfaces are modified from Reheis et al. (1993). See Table 1 for the detailed measurements of 659 scarp heights. 660 661 Figure 7: Hillshaded LiDAR-derived DEM of the Indian Creek site showing the topographic 662 profiles analyzed. The number by each fault scarp corresponds to the fault number in Table 1. 663 The mapped Quaternary surfaces are modified from Reheis et al. (1995). See Table 1 for the 664 detailed measurements of scarp heights. 665 666 Figure 8: Geometry of an ideal fault scarp, after Hanks et al. (1984). S- surface offset or scarp 667 offset; 2H- scarp height; θf- far-field slope angle; θs- scarp slope angle. 668 669 Figure 9: Representative examples of sampled boulders from (a) the Qfm deposit at Wildhorse 670 Creek, and (b) the Qfi deposit at Perry Aiken Creek. 671 672 Figure 10: Probability density functions of the 10Be ages from surface boulders. (a) Probability 673 density function of the six samples used to determine the age of Qfm at Wildhorse Creek. (b) 674 Probability density function of the nine samples used to determine the age of Qfi at Perry Aiken 675 Creek. The uncertainties are reported as the mean and standard deviation. 676 677 Figure 11: Rates of extension on faults in the ECSZ between 37° N and 38° N latitude. The rates 678 on the Round Valley fault (RVF) and Hilton Creek fault (HCF) are from Berry (1997), the rate 679 in the Volcanic Tablelands is determined by Sheehan, T. and Dawers, N. (2005), the rate on the 680 White Mountains fault (WMF) is from Kirby et al. (2006), and the rates on the FLVF are from Ganev et al., 2009 Page 25 681 this study. In some of the aforementioned publications the authors report only the vertical 682 component of slip; therefore, we resolve the extension rates by assuming a 60° fault dip on the 683 faults. DSF- Deep Springs fault, EPF- Emigrant Peak fault, FLVF- Fish Lake Valley fault, HCF- 684 Hill Creek fault, OVF- Owens Valley fault, QVF- Queen Valley fault, RVF- Round Valley fault. 685 686 Figure 12: Fault model showing the development of northeast-striking normal faults transferring 687 strain in a right stepover between two northwest-striking zones of right-lateral shear. Clockwise 688 rotation of the normal faults is necessary to achieve the highest efficiency in slip transfer. Along 689 the FLVF the right-lateral slip rate decreases northward near the Mina Deflection where there is 690 an increase in the extension rate of the fault zone. These observations suggest the possible 691 development of a nascent strain transfer system between the northern ECSZ and Walker Lane. 692 693 Tables 694 Table 1: Measured vertical and calculated horizontal offsets from profiles. 695 696 Table 2: Analytical results of terrestrial cosmogenic nuclide 10Be geochronology for the 697 Wildhorse Creek and Perry Aiken Creek alluvial fans in Fish Lake Valley. 698 699 Data Repository Figure Caption 700 Figure DR1: Complete list of the analyzed topographic profiles across alluvial fan surfaces and 701 calculated vertical components of displacement from the four study sites: (a) Furnace Creek; (b) 702 Wildhorse Creek; (c) Perry Aiken Creek; (d) Indian Creek. See Figures 4-7 for locations of the 703 profiles. Ganev et al., 2009 Page 26 704 705 Figures 706 Figure 1: Topographic map and Quaternary faults in the northern ECSZ. Fish Lake Valley fault 707 is shown in white. The corners of Figure 2 are shown in black. Faults are from the USGS 708 Quaternary fault and fold database. AHF- Ash Hill fault, ALF- Airport Lake fault, BSF- Benton 709 Springs fault, CF- Coaldale fault, EF- Excelsior Mountains fault, EPF- Emigrant Peak fault, 710 EVF- Eureka Valley fault, DSF- Deep Springs fault, FLVF- Fish Lake Valley fault, GF- Garlock 711 fault, HCF- Hilton Creek fault, HMSVF- Hunter Mountain-Saline Valley fault, LMF- Lone 712 Mountain fault, MLF- Mono Lake fault, NDVF- northern Death Valley fault, OVF- Owens 713 Valley fault, PSF- Petrified Springs fault, PVF- Panamint Valley fault, QVF- Queen Valley fault, 714 RF- Rattlesnake Flat fault, RVF- Round Valley fault, SLF-Silver Lake fault, SNF- Sierra Nevada 715 frontal fault, SVF- Saline Valley fault, TMF- Tin Mountain fault, TPF- Towne Pass fault, WF- 716 Warm Springs fault, WMF- White Mountains fault. GPS strain accumulation rates from Bennett 717 et al. [2003]. Ganev et al., 2009 Page 27 718 Ganev et al., 2009 Page 28 719 Figure 2: Detailed index map of the study area. The locations of our study sites are labeled 1 720 through 4 from south to north: 1- Furnace Creek; 2- Wildhorse Creek; 3- Perry Aiken Creek; 4- 721 Indian Creek. DSF- Deep Springs fault, EPF- Emigrant Peak fault, FLVF- Fish Lake Valley 722 fault, OVF- Owens Valley fault, QVF- Queen Valley fault; WMF- White Mountains fault. 723 724 Ganev et al., 2009 Page 29 725 Figure 3: Selected topographic profiles across alluvial fan surfaces and calculated vertical 726 components of displacement from the four study sites: (a) Furnace Creek; (b) Wildhorse Creek; 727 (c) Perry Aiken Creek; (d) Indian Creek. See Figures 4-7 for locations of the profiles. 728 Ganev et al., 2009 Page 30 729 Figure 4: Hillshaded LiDAR-derived DEM of the Furnace Creek site showing the topographic 730 profiles analyzed. The number by each fault scarp corresponds to the fault number in Table 1. 731 The mapped Quaternary surfaces are modified from Reheis et al. (1993). See Table 1 for the 732 detailed measurements of scarp heights. 733 734 735 736 737 Ganev et al., 2009 Page 31 738 Figure 5: Hillshaded LiDAR-derived DEM of the Wildhorse Creek site showing the topographic 739 profiles analyzed. The green dots indicate the locations of the dated samples. The number by 740 each fault scarp corresponds to the fault number in Table 1. The mapped Quaternary surfaces are 741 modified from Reheis et al. (1993). See Table 1 for the detailed measurements of scarp heights. 742 743 744 745 Ganev et al., 2009 Page 32 746 Figure 6: Hillshaded LiDAR-derived DEM of the Perry Aiken Creek site showing the 747 topographic profiles analyzed. The green dots indicate the locations of the dated samples. The 748 number by each fault scarp corresponds to the fault number in Table 1. The mapped Quaternary 749 surfaces are modified from Reheis et al. (1993). See Table 1 for the detailed measurements of 750 scarp heights. 751 752 753 754 Ganev et al., 2009 Page 33 755 Figure 7: Hillshaded LiDAR-derived DEM of the Indian Creek site showing the topographic 756 profiles analyzed. The number by each fault scarp corresponds to the fault number in Table 1. 757 The mapped Quaternary surfaces are modified from Reheis et al. (1995). See Table 1 for the 758 detailed measurements of scarp heights. 759 760 761 762 763 764 Ganev et al., 2009 Page 34 765 766 Figure 8: Geometry of an ideal fault scarp, after Hanks et al. (1984). S- surface offset or scarp 767 offset; 2H- scarp height; θf- far-field slope angle; θs- scarp slope angle. 768 769 770 771 772 Figure 9: Representative examples of sampled boulders from (a) the Qfm deposit at Wildhorse 773 Creek, and (b) the Qfi deposit at Perry Aiken Creek. 774 775 776 777 778 Ganev et al., 2009 Page 35 779 780 781 782 Figure 10: Probability density functions of the 10Be ages from surface boulders. (a) Probability 783 density function of the six samples used to determine the age of Qfm at Wildhorse Creek. (b) 784 Probability density function of the nine samples used to determine the age of Qfi at Perry Aiken 785 Creek. The uncertainties are reported as the mean and standard deviation. 786 787 788 789 790 791 792 793 Ganev et al., 2009 Page 36 794 795 796 797 Figure 11: Known rates of extension on faults in the ECSZ between 37° N and 38° N latitude. 798 The rates on the RVF and HCF are by Berry (1997), the rate in the Volcanic Tablelands is 799 determined by Sheehan, T. and Dawers, N. (2005), the rate on the WMF is published by Kirby et 800 al. (2006), and the rates on the FLVF are from this study. In some of the aforementioned 801 publications the authors report only the vertical component of slip; therefore, we resolve the 802 extension rates by assuming a 60° fault dip on the faults. DSF- Deep Springs fault, EPF- 803 Emigrant Peak fault, FLVF- Fish Lake Valley fault, HCF- Hill Creek fault, OVF- Owens Valley 804 fault, QVF- Queen Valley fault, RVF- Round Valley fault. Ganev et al., 2009 Page 37 805 806 807 Figure 12: Fault model showing the development of northeast-striking normal faults transferring 808 strain in a right stepover between two northwest-striking zones of right-lateral shear. Clockwise 809 rotation of the normal faults is necessary to achieve the highest efficiency in slip transfer. Along 810 the FLVF the right-lateral slip rate decreases northward near the Mina Deflection where there is 811 an increase in the extension rate of the fault zone. These observations suggest the possible 812 development of a nascent strain transfer system between the northern ECSZ and Walker Lane. Ganev et al., 2009 Page 38 813 814 815 816 817 818 819 Ganev et al., 2009 Page 39 820 TABLES 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 Ganev et al., 2009 Page 40 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 Ganev et al., 2009 Page 41 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 Ganev et al., 2009 Page 42 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 Data Repository Figure 911 Figure DR1: Complete list of the analyzed topographic profiles across alluvial fan surfaces and 912 calculated vertical components of displacement from the four study sites: (a) Furnace Creek; (b) 913 Wildhorse Creek; (c) Perry Aiken Creek; (d) Indian Creek. See Figures 4-7 for locations of the 914 profiles. Ganev et al., 2009 Page 43 915 Ganev et al., 2009 Page 44 916 Ganev et al., 2009 Page 45 917 Ganev et al., 2009 Page 46 918 Ganev et al., 2009 Page 47 919 Ganev et al., 2009 Page 48