Late Pleistocene slip on a low-angle normal fault, Searles Valley, California

Abstract

The mechanical feasibility of normal-sense slip on low-angle faults remains a conundrum in extensional tectonics. The rarity of demonstrably active low-angle normal faults may imply that very specifi c criteria must be satisfi ed for signifi cant fault displacement. We present new geologic observations, geomorphic mapping, and structural analysis for a low-angle fault zone along the eastern margin of Searles Valley, California. Our observations indicate thatPleistocene displacement along the range-front fault scarps is the near-surface expression of slip on a bedrock-rooted low-angle normal fault. Along the central portion of the range front in Searles Valley, high-angle faults offset late Pleistocene alluvial and lacustrine surfaces. These faults merge downward into a westdipping, low-angle fault, but do not displace the low-angle surface. These geometric relations are satisfi ed only when displacement on the high-angle faults is accommodated by slip on the basal low-angle fault. We use displaced alluvial fan surfaces to determine slip rates across the fault system over late Pleistocene to Holocene time. Combining radiocarbon ages of lacustrine tufa deposits with high-precision topographic surveys of fault scarps yields average slip rates of 0.21-0.35 m/k.y. Additional mapping of faults within the Slate Range at the northern end of Searles Valley suggests that slip is transferred northward to the Manly Pass fault, a bedrock normal fault that trends northeast into Panamint Valley. Thus, although displacement along the range-front fault system dies out northward, we infer that active deformation occurs within the range and likely links extension in Searles Valley with deformation in Panamint Valley.

Middle Miocene to recent exhumation of the Slate Range, eastern California, and implications for the timing of extension and the transition to transtension

“…2) parallels Layton Canyon. This work complements studies of late Cenozoic deformation in the southern and northern Slate Range (Walker et al, 2005;Numelin et al, 2007;Andrew and Walker, 2009). …”

“…2; Moore, 1976;Smith et al, 1968;Walker et al, 2005;Numelin et al, 2007). Pre-Cenozoic rocks along the northern transect consist of 100 Ma Stockwell diorite, 159 Ma Copper Queen alaskite, and 166 Ma Isham Canyon granite (Moore, 1976;Dunne and Walker, 2004) containing pendants of Paleozoic and Mesozoic metasedimentary rocks.…”

Strain transfer and partitioning between the Panamint Valley, Searles Valley, and Ash Hill fault zones, California

“…Thus, scarp formation is interpreted to reflect slip on the normal fault zone within the past 25-10 ka. Motion on this zone appears to be primarily dip-slip (with the horizontal component of slip trending ϳ270Њ); channels and debris-flow levees are not offset laterally by any significant amount across the graben and the fault trace is very sinuous as followed across topography (Numelin and Kirby, 2004). The low-angle normal fault is continuous northward with the Sand Canyon ''thrust'' mapped by Smith et al (1968).…”

“…1), the scarps form a graben in alluvial fan deposits with a moderately well developed pavement. Stratigraphic observations indicate that alluvial fan gravel overlies carbonate-cemented beach gravel along most of the range front (Numelin and Kirby, 2004). These fans are overlapped along their distal margins by distinct shoreline features, including wave-cut platforms, tufa mounds, and beach deposits.…”

Temporal variations in Holocene slip rate along the central Garlock fault, Pilot Knob Valley, California

“…Fault systems of the Eastern California shear zone terminate both north and south of the Garlock (Oskin and Iriondo, 2004;Numelin et al, 2007) and do not appear to signifi cantly disrupt the western and central segments of the fault zone (e.g., McGill and Sieh, 1991).…”