Testing a kinematic and geometric fault slip transfer model: Geologic and LIDAR mapping and

Transcription

1 Testing a kinematic and geometric fault slip transfer model: Geologic and LIDAR mapping and 40Ar/ 39 Ar Geochronology in the northern Eastern California Shear Zone, California MS Thesis Candidate: Kevin M DeLano, delano@geology.cwu.edu MS Thesis Supervisor: Dr. Jeffrey Lee, jeff@geology.cwu.edu Introduction The spatial and temporal distribution of strain across the Walker Lane Belt (WLB) Eastern California Shear Zone (ECSZ), which accommodates ~20% of Pacific-North America plate motion, is a major tectonic question. To characterize the evolution of fault kinematics and determine the mechanisms of intracontinental deformation, geologists compare geodetic and geologic slip rates. Across the northern ECSZ, at 37.5 N-38 N, the sum of geologically determined fault slip rates is ~33% of the geodetically determined NW dextral shear rate (Frankel et al., 2011). To resolve part of this discrepancy, Nagorsen-Rinke et al. (2013) proposed a kinematic fault slip transfer model whereby NW dextral shear is transferred from the Owens Valley fault (OVF) north-northwest to the Mina deflection via undocumented slip. To test this model, I will accomplish new field geologic mapping and structural, kinematic, and 40 Ar/ 39 Ar geochronology studies to determine the faulting and volcanic histories of the Black Mountain area and LiDAR mapping of faults in the Volcanic Tableland. I will use anticipated Pliocene to Pleistocene fault slip rates for the Black Mountain area and Volcanic Tableland to address regional tectonic questions, including the discrepancy between geodetic and geologic fault slip rates, the spatial and temporal distribution of strain in the northern ECSZ, and the relative contributions of geodynamic forces driving deformation at the northern margin of the ECSZ. Background and Importance Figure 1. Shaded relief map of the northern Eastern California Shear Zone and western Basin and Range Province, showing major Quaternary faults. Solid circles are on the hanging wall of normal faults; arrows indicate relative motion across strike-slip faults. Modified from Lee et al. (2009). Transform motion between the Pacific and North American plates is partitioned between the San Andreas Fault system (~80% of the plate motion) and the WLB-ECSZ (~20% of the plate motion). Fault slip across the

2 DeLano MS Thesis Proposal 2 WLB-ECSZ is characterized by a dominant set of NW-striking dextral faults, which strike sub-parallel to Pacific- North America plate motion, and lesser NS-striking to NE-striking normal faults, and ENE-striking sinistral faults (Fig. 1). Numerous investigations along the WLB-ECSZ have centered on documenting fault slip rates over geologic and geodetic time scales. Across a NEstriking transect of northern ECSZ at latitude 37.5 N-38 N, a discrepancy exists between geologic and geodetic slip rates (Fig. 2). The sum of geologic fault slip rates is ~33% of the geodetic NW dextral shear rate, 10 mm/yr (Frankel et al., 2011; Lifton et al., 2013). To resolve part of the discrepancy, Nagorsen-Rinke et al. (2013) proposed a fault slip kinematic model whereby NW dextral shear along the NNW-striking dextral Owens Valley fault (OVF) is transferred north-northwest to ENEstriking faults in the Mina deflection (Fig. 3). In this kinematic model, NW dextral shear at the northern margin of the OVF is transferred northward via two components: (a) one component to the northeast along the NW-striking dextral White Mountains fault zone (WMFZ), which accommodates ~ mm/yr (Kirby et al., 2006) to 1.1 mm/yr of slip (Lifton et al., 2013) and (b) a second component to the northwest through the Volcanic Tableland, into the Black Mountain area, and onto faults in the Adobe Hills via ~0.6 mm/yr ~EW-extension on NNE-striking normal faults since the Pliocene. Fault slip rates in the Black Mountain area can be constrained because faults offset datable Miocene to Pleistocene volcanic rock units. Slip rates in the Volcanic Tableland can be constrained via LiDAR mapping because faults show measurable offset in the Bishop tuff, a 759 ka pyroclastic flow. Through new geologic field

3 DeLano MS Thesis Proposal 3 mapping, structural geology, and 40 Ar/ 39 Ar geochronology in the Black Mountain area and LiDAR mapping across the Volcanic Tableland, I will document fault slip kinematics, magnitude of fault slip, timing of volcanism, and fault slip rates over time. My results will allow me to test the Nagorsen-Rinke et al. (2013) kinematic model and address regional tectonic questions, including the local discrepancy between geodetic and geologic slip rates, the spatial and temporal distribution of regional strain in the northern ECSZ, and the relative contributions of plate boundary vs. gravitational potential energy forces in driving deformation within this area of the ECSZ. Geologic Setting The northern ECSZ (Fig. 1) is a ~ km wide domain of NW dextral shear that extends from the ENEstriking Garlock fault north to the Mina deflection, a fault slip transfer zone that relays dextral shear from the northern ECSZ, across a ~60 km right-stepover, to the Central Walker Lane Belt. Starting ~12 Ma, intracontinental Pacific-North American dextral shear initiated on NW-striking dextral faults in the northern ECSZ (Faulds and Henry, 2008). The Pliocene delamination of the lithospheric root beneath the Sierra Nevada changed regional lithospheric heat flow dynamics, and is a proposed driver of the westward shift in E-W extension and regional dextral shear (Jones et al., 2004). Fault slip rates decreased on the Fish Lake Valley-Death Valley fault zone and increased on the White Mountains- Owens Valley fault zone (Malservisi et al., 2001; Nagorsen-Rinke et al., 2013; Saleeby et al., 2012). Today, overlapping NW-striking dextral faults, connected by NEstriking normal faults, accommodate NW dextral shear (Lee et al., 2001; Faulds and Henry, 2008). Faulting History of the Owens Valley Exposed within the Owens Valley, a ~175 km long extensional graben, is the White Mountains-Owens Valley fault zone, one of the major NW-striking dextral faults that accommodates shear across the ECSZ (Lee et al.,

4 DeLano MS Thesis Proposal ). The Owens Valley fault is a ~55 km long, NNW-striking, dextral fault system (Fig. 3). Dextral slip along the OVF, or its precursor structure, initiated ~83 Ma and accommodated km of dextral slip during the Late Cretaceous and early Tertiary (Glazner et al., 2005). About 3 Ma, the westward shift in regional dextral shear reactivated the OVF as a complex system of dextral, normal, and oblique faults (Glazner et al., 2005; Stockli et al., 2003). Since reactivation, the OVF has accommodated ~6-9 km of dextral displacement (Glazner et al., 2005) Nagorsen-Rinke et al. (2013) proposed that the OVF transfers slip to the Mina deflection via two components: (a) an eastward step onto the dextral White Mountains fault zone (WMFZ) and (b) a predicted northwestward step onto a set of faults that cut across the Volcanic Tableland (Figs. 2 and 3). The WMFZ is a ~60 km long, NWstriking, dextral-normal oblique fault system (Fig. 1). Slip along the WMFZ initiated ~12 Ma as a normal fault, accommodated 8 km of west-down horizontal displacement, and uplifted the modern White Mountains. Since strike-slip initiated ~3 Ma, the WMFZ has accommodated km of dextral displacement (Stockli et al., 2003). Slip rates on the OVF and WMFZ appear to have varied temporally since the Pleistocene. Late Pleistocene (80-55 ka) dextral slip on the northern OVF was calculated at 2.8 mm/yr ± error (Kirby et al., 2008), wheras the latest Pleistocene (25 ka) dextral slip rate on the southern OVF was calculated at 1.0 ± 0.5 mm/yr (Bacon and Pezzopane, 2007). The discrepancy in slip rates suggests that either slip on the OVF decreased during the late Pleistocene or that slip across the southern Owens Valley is distributed across a broad deformation zone rather than concentrated on a single fault stand. Of the latter is true, then the dextral slip rate estimate of Bacon and Pezzopane (2007) is an underestimate for the total slip rate across the southern Owens Valley. A minimum dextral slip rate of 1.1 ± 0.1 mm/yr since the eruption of the Bishop tuff (~759 ka) was calculated for the WMFZ (Lifton, 2013). An investigation by (Kirby et al., 2006) suggested that dextral slip rates decreased to mm/yr along the WMFZ since the late Pleistocene (90-60 ka). In contrast, a more recent investigation by (Lifton, 2013) yielded late Pleistocene slip rates of /-0.4 to /-0.7 mm/yr, indicating that the slip rate likely remained constant through time. Geodetic measurements yield a modern slip rate of 1.9 mm/yr of slip (Lifton et al., 2013), a rate consistent with the idea that slip rates along the WMFZ have been constant through time. North of Owens Valley and west of the WMFZ, distributed NS-striking normal faults and NW-striking dextral faults across the Volcanic Tableland, NNE-striking normal faults exposed in the Black Mountain area, and NW-striking normal-oblique faults exposed in the southern Adobe Hills area transfer NW dextral shear from the OVF to sinistral faults in the Mina deflection (Fig. 3) (Nagorsen-Rinke et al., 2013). The ± 1.8 ka Bishop tuff, a pyroclastic flow deposit, defines the Volcanic Tableland (Bogaard and Schirnick, 1995; Sarna-Wojcicki et al., 2000). Tectonic geomorphology clearly shows that from south to north across part of the Volcanic Tableland, NS-striking normal faults swing into NW-striking dextral faults and in turn swing back into NS-striking normal faults (Fig. 4). These faults cut the Bishop tuff, which provides an ideal time-datum for documenting Pleistocene fault slip rates. North of the Volcanic Tableland, the distributed faults consolidate onto NNE-striking normal

5 DeLano MS Thesis Proposal 5 faults in the Black Mountain area. Faults in the Black Mountain area cut Jurassic granitic basement and scattered Miocene to Pleistocene volcanic flows and tuffs. Faults are buried under or cut Quaternary deposits. Geologic slip rates on faults in the Volcanic Tableland and Black Mountain area have not been documented.

6 DeLano MS Thesis Proposal 6 Based on the Nagorsen-Rinke et al. (2013) kinematic model (Fig. 3), we predict that NW-striking faults cutting the Volcanic Tableland accommodate ~0.4 mm/yr dextral shear and that NNE-striking normal faults in the Black Mountain area (Fig. 2) accommodate 0.6 mm/yr of ~EW-extension. Research Plan To test the Nagorsen-Rinke et al. (2013) fault slip kinematic model, I will accomplish new field geologic mapping and structural, kinematic, geomorphic and 40 Ar/ 39 Ar geochronology studies to determine the faulting and volcanic histories of the Black Mountain area and LiDAR mapping of faults across the Volcanic Tableland (Fig. 2). The combination of desert exposure, well-preserved fault geometry and geomorphic indicators, and faulting through datable Miocene to Pleistocene volcanic rocks make the Black Mountain area and Volcanic Tableland excellent locations to study fault kinematics within the northern ECSZ. Field geologic mapping in the Black Mountain area will be done on 1:12,000 digital orthophotoquadrangles georeferenced to DEM contours and supported with structural and kinematic field data. My field focus will be to map faults that cut Miocene to Pleistocene volcanic and sedimentary rock units which unconformably overlie Mesozoic granitic rocks (Krauskopf and Bateman, 1977). To constrain fault geometry, kinematics, and offset, I will use use stratigraphy, bedrock orientation, fault plane and striation orientations, cross-cutting relationships, and geomorphic indicators. Field work will be conducted from June 2 to August 3, 2014 with advisor supervision at the beginning, middle, and end of the field season. Two field assistants, Tucker Lance and Peter Duboyski, will accompany me for the duration of fieldwork. I will combine 40 Ar/ 39 Ar geochronology with fault offset measurements to calculate fault slip rates, a key dataset that will allow me to determine the spatial and temporal evolution of faulting in the Black Mountain area and test and refine the Nagorsen-Rinke et al. (2013) fault slip kinematic model. Under the supervision of Dr. Andy Calvert, a collaborator of Dr. Jeffrey Lee, 40 Ar/ 39 Ar geochronology of volcanic rock units cut by and depositionally overlying faults will be conducted at the USGS, Menlo Park, CA. Two 1-week trips are needed: (1) the first week, in late Fall 2014, will be spent crushing samples, separating appropriate minerals for 40 Ar/ 39 Ar geochronology, and packaging the mineral separates for irradiation, and (2) the second week, in late Spring 2015, will be spent assisting with extracting the gas for 40 Ar/ 39 Ar geochronology. To determine the faulting history of the Volcanic Tableland, I will use high-resolution LiDAR topography to map faults and calculate the magnitude of horizontal ~EW-extension across the NS-striking normal faults and horizontal NE-SW extension across the NW-striking faults (Fig. 4). Using simple trigonometry, I can then calculate the magnitude of NW dextral shear across the zone of NW-striking normal-dextral oblique faults (Fig. 5). Geologic slip rates can then be calculated by dividing the magnitude of offsets by the ~759 ka age of the Bishop tuff (Bogaard and Schirnick, 1995; Sarna-Wojcicki et al., 2000). The combination of desert exposure, well-preserved fault geometry, and faulting through a single time datum make the Volcanic Tableland an

7 DeLano MS Thesis Proposal 7 excellent site to document Pleistocene geologic slip rates, and to test and refine the Nagorsen-Rinke et al. (2013) kinematic model. My new geologic mapping, structural geology, and 40 Ar/ 39 Ar geochronology studies of the Black Mountain area and LiDAR mapping of the Volcanic Tableland will also allow me to address regional tectonic questions, including (a) whether the local discrepancy between geodetic and geologic slip rates is real, (b) the spatial and temporal distribution of regional strain in the northern ECSZ, and (c) assessing the relative contributions plate boundary vs. gravitational potential energy forces in driving deformation in this part of the ECSZ (Jones et al., 2004; Saleeby et al., 2012).

8 DeLano MS Thesis Proposal 8 Schedule Spring 2014 o Defend thesis proposal (Friday May 23 at 9am) o Start writing background of thesis? o Investigation of faults in Volcanic Tableland from LiDAR data o Submit GSA meeting abstract for LiDAR project Summer 2014 o June 2 August 3: two month field season in Black Mountain area, Mono County, CA o August: Spend time in California o September: Return to Washington Fall 2014 o Select volcanic rock samples for thin sectioning and 40 Ar/ 39 Ar geochronology o Compile geologic map, cross sections, structural data, and stratigraphic observations, and complete limited petrography on volcanic rocks o October - Present LiDAR mapping research at GSA in Vancouver o Write background, methods, and preliminary results section of thesis o October or November - First trip to USGS Menlo Park to prepare samples for 40 Ar/ 39 Ar geochronology Winter 2015 o Complete analyses o Complete figures o Finish writing background, methods, and available results Spring 2015 o Second trip to USGS Menlo Park to complete geochronology o Finish writing thesis o Defend thesis in early June Summer 2015 o Go boating, travel, celebrate Budget Field Work Large pickup truck rental from Enterprise in Bishop, CA: $ K.DeLano stipend: $6000-$7000 WMRC lodging: $880 - covered T. Lance stipend: $2000 Receieved $1000 from NCGS 40 Ar/ 39 Ar geochronology, $2160

9 DeLano MS Thesis Proposal 9 Item Explanation Single Trip Cost Two Trip Total Airfare Two round trip flights - Seattle to San Jose $400 $800 Ground Two round trip airport shuttles in Washington $70 $140 Transportation - Ellensburg, WA to Seattle, WA Ground Two round Caltrain tickets in California - San $10 $20 Transportation Jose Airport to Menlo Park Inn Hotel 12 nights at Pacific Euro $70/night $420 $840 Food per diem $30/day for 12 days $180 $360 Grand Total $2160 GSA funded -$1500 Remaining $616 Anticipated Support 1) USGS-EDMAP (funded). $17499 awarded to Dr. Jeffrey Lee for fieldwork only. 2) Northern California Geological Society (funded), $1000 awarded to K. DeLano for fieldwork. 3) National Center for Airborne Laser Mapping (funded), awarded to K. DeLano for LiDAR dataset across a portion of the Volcanic Tableland for mapping faults. 4) GSA Graduate Research Grant (funded), $1500 awarded to K. DeLano to support 40 Ar/ 39 Ar geochronology analysis at USGS, Menlo Park, CA. 5) White Mountain Research Station minigrant (funded), awarded $880 to K. DeLano to cover lodging once every 10 days during fieldwork 6) Northwest Federation of Mineralogical Societies - American Federation of Mineralogical Societies Scholarship Foundation (funded), awarded $4000 scholarship to K. DeLano. 7) Two Central Washington University graduate student research fellowships (pending), applied for $700 and $2800 to support 40 Ar/ 39 Ar geochronology and a summer stipend for fieldwork. 8) Central Washington University general scholarship application (pending) for funding to cover tuition expenses. References Bacon, S.N., and Pezzopane, S.K., 2007, A 25,000-year record of earthquakes on the Owens Valley fault near Lone Pine, California: Implications for recurrence intervals, slip rates, and segmentation models: Geological Society of America Bulletin, v. 119, no. 7-8, p , doi: /B Bogaard, P. van den, and Schirnick, C., 1995, 40Ar/39Ar laser probe ages of Bishop Tuff quartz phenocrysts substantiate long-lived silicic magma chamber at Long Valley, United States: Geology, v. 23, no. 8, p. 759, doi: / (1995)023<0759:AALPAO>2.3.CO;2. Dixon, T.H., Miller, M., Farina, F., Wang, H., and Johnson, D., 2000, Present-day motion of the Sierra Nevada block and some tectonic implications for the Basin and Range province, North American Cordillera: Tectonics, v. 19, no. 1, p Faulds, J.E., and Henry, C.D., 2008, Tectonic influences on the spatial and temporal evolution of the Walker Lane: An incipient transform fault along the evolving Pacific North American plate boundary: Ores and orogenesis: Circum-Pacific tectonics, geologic evolution, and ore deposits: Arizona Geological Society Digest, v. 22, p Frankel, K.L., Dolan, J.F., Owen, L.A., Ganev, P., and Finkel, R.C., 2011, Spatial and temporal constancy of seismic strain release along an evolving segment of the Pacific North America plate boundary: Earth and Planetary Science Letters, v. 304, no. 3-4, p , doi: /j.epsl

10 DeLano MS Thesis Proposal 10 Glazner, A.F., Lee, J., Bartley, J.M., Coleman, D.S., Kylander-Clark, A., Greene, D.C., and Le, K., 2005, Large dextral offset across Owens Valley, California from 148 ma to 1872 A.D., in Stevens, C. and Cooper, J. eds., Western Great Basin Geology, 99, The Pacific Section Society of Sedimentary Geology, p Jones, C.H., Farmer, G.L., and Unruh, J., 2004, Tectonics of Pliocene removal of lithosphere of the Sierra Nevada, California: Geological Society of America Bulletin, v. 116, no , p Kirby, E., Anandakrishnan, S., Phillips, F., and Marrero, S., 2008, Late Pleistocene slip rate along the Owens Valley fault, eastern California: Geophysical Research Letters, v. 35, no. 1, doi: /2007GL Kirby, E., Burbank, D.W., Reheis, M., and Phillips, F., 2006, Temporal variations in slip rate of the White Mountain Fault Zone, Eastern California: Earth and Planetary Science Letters, v. 248, no. 1-2, p , doi: /j.epsl Krauskopf, K.B., and Bateman, P.C., 1977, Geologic Quadrangle Map, Glass Mountain Quadrangle, California-Nevada: U.S. Dept. of the Interior, U.S. Geological Survey, Washington DC. Lee, J., Spencer, J., and Owen, L., 2001, Holocene slip rates along the Owens Valley fault, California: Implications for the recent evolution of the eastern California shear zone: Geology, v. 29, no. 9, p Lee, J., Stockli, D.F., Owen, L.A., Finkel, R.C., and Kislitsyn, R., 2009, Exhumation of the Inyo Mountains, California: Implications for the timing of extension along the western boundary of the Basin and Range Province and distribution of dextral fault slip rates across the eastern California shear zone: Tectonics, v. 28, no. 1, doi: /2008TC Lifton, Z.M., 2013, Understanding an evolving diffuse plate boundary with geodesy and geochronology [PhD thesis]: Georgia Institute of Technology, 108 p. Lifton, Z.M., Newman, A.V., Frankel, K.L., Johnson, C.W., and Dixon, T.H., 2013, Insights into distributed plate rates across the Walker Lane from GPS geodesy: Geophysical Research Letters, v. 40, p , doi: /grl Malservisi, R., Furlong, K.P., and Dixon, T.H., 2001, Influence of the earthquake cycle and lithospheric rheology on the dynamics of the eastern California shear zone: Geophysical Research Letters, v. 28, no. 14, p Nagorsen-Rinke, S., Lee, J., and Calvert, A., 2013, Pliocene sinistral slip across the Adobe Hills, eastern California western Nevada: Kinematics of fault slip transfer across the Mina deflection: Geosphere, v. 9, no. 1, p Saleeby, J., Le Pourhiet, L., Saleeby, Z., and Gurnis, M., 2012, Epeirogenic transients related to mantle lithosphere removal in the southern Sierra Nevada region, California, part I: Implications of thermomechanical modeling: Geosphere, v. 8, no. 6, p , doi: /GES Sarna-Wojcicki, A.M., Pringle, M.S., and Wijbrans, J., 2000, New 40Ar/39Ar age of the Bishop Tuff from multiple sites and sediment rate calibration for the Matuyama-Brunhes boundary: Journal of Geophysical Research: Solid Earth ( ), v. 105, no. B9, p Stockli, D.F., Dumitru, T.A., McWilliams, M.O., and Farley, K.A., 2003, Cenozoic tectonic evolution of the White Mountains, California and Nevada: Geological Society of America Bulletin, v. 115, no. 7, p