Two‐phase westward encroachment of Basin and Range extension into the northern Sierra Nevada

Abstract

[1] Structural, geophysical, and thermochronological data from the transition zone between the Sierra Nevada and the Basin and Range province at latitude $39°N suggest $100 km westward encroachment of Basin and Range extensional deformation since the middle Miocene. Extension, accommodated primarily by east dipping normal faults that bound west tilted, range-forming fault blocks, varies in magnitude from <2% in the interior of the Sierra Nevada crustal block to >150% in the Wassuk and Singatse Ranges to the east. Geological and apatite fission track data from exhumed upper crustal sections in the Wassuk and Singatse Ranges point to rapid footwall cooling related to large magnitude extension starting at $14 -15 Ma. Farther to the west, geological and thermochronological data indicate a younger period of extension in the previously unextended Pine Nut Mountains, the Carson Range, and the Tahoe-Truckee depression initiated between 10 Ma and 3 Ma, and incipient post-0.5 Ma faulting to the west of the Tahoe-Truckee area. These data imply the presence of an extensional breakaway zone between the Singatse Range and the Pine Nut Mountains at $14 -15 Ma, forming the boundary between the Sierra Nevada and Basin and Range at that time. In addition, fission track data imply a Miocene preextensional geothermal gradient of 27 ± 5°C km À1 in the central Wassuk Range and 20 ± 5°C km À1 in the Singatse Range, much higher than the estimated early Tertiary gradient of 10 ± 5°C km À1 for the Sierra Nevada batholith. This might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting. Apatite fission track, geophysical, and geological constraints across the Sierra Nevada-Basin and Range transition zone indicate a twostage, coupled structural and thermal westward encroachment of the Basin and Range province into the Sierra Nevada since the middle Miocene.

The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

“…We suggest that the Wassuk Range has played and continues to play a significant role in the accommodation of extension across the Walker Lane at the latitude of Lake Tahoe, consistent with previous studies of the central Walker Lane and the Wassuk Range (e.g., Stewart, 1988;Surpless et al, 2002;Oldow, 2003;Wesnousky, 2005;Surpless, 2008;Wesnousky et al, 2012;Dong et al, 2014). The long-term rate of vertical displacement along the Wassuk fault is comparable to the most active fault systems in the western Basin and Range, including faults along the western margin of the Lake Tahoe basin (0.85 -1.7 mm/yr; Fig.…”

“…13a). Interestingly, this would suggest that most of the present-day relief of the Wassuk Range has been produced since ∼4 Ma, consistent with the results of structural reconstructions and thermochronologic data that suggest a renewed pulse of normal fault motion starting at that time Surpless et al, 2002;Surpless, 2011). Importantly, we suggest that our new slip rate estimate for the 10 5 -yr timescale spans sufficient time that the effects of earthquake clustering, on the ∼10 4 -yr timescale (e.g., Friedrich et al, 2003), are negligible in time-averaged displacement rate calculations (Fig.…”

“…The impressive topographic relief along the fault zone and previous geologic studies have established that displacement along the fault zone has been characterized by significant normal displacement across all time scales during Tertiary and Quaternary time (e.g., Dilles, 1993;Stockli et al, 2002;Surpless et al, 2002;Wesnousky, 2005;Surpless, 2011;Bormann et al, 2012;Wesnousky et al, 2012;Dong et al, 2014).…”

Cenozoic tectonic evolution of the central Wassuk Range, western Nevada, USA

“…During this period, extensional deformation migrated to the west, affecting the Pine Nut Mountains, the Carson Range, and the area to the west of Lake Tahoe ( Fig. 2; e.g., Dilles and Gans, 1995;Surpless et al, 2002;Cashman et al, 2009), potentially related to changes in the thermal structure of the crust (e.g., Surpless et al, 2002). Although the timing of the initiation of the second generation of normal faults is poorly constrained in the study area, these faults were clearly active during Wassuk Group sedimentation from ~9.5 -7 Ma.…”

“…2; e.g., Proffett, 1977;Dilles and Gans, 1995;Schweickert et al, 2000;Stockli et al, 2002;Surpless et al, 2002). Thus, the Wassuk Range is considered the approximate boundary between active dextral motion associated with the Walker Lane and Basin and Range extension (e.g., Oldow et al, 1994;2003;Wesnousky, 2005;Surpless, 2008).…”