Crustal Deformation in the Sierra Nevada and Walker Lane Region Inferred From P‐Wave Azimuthal Anisotropy

Abstract

The Sierra Nevada and Walker Lane region is located in the transition zone between the Pacific and North American plates (Figure 1). The long-term Mesozoic-Cenozoic subduction and subsequent right-lateral transform motion of the plate boundary have jointly contributed to the formation of its major tectonic units, including a volcanic arc (Sierra Nevada Batholith, SNB), an island arc complex (Sierra Nevada Metamorphic Belt, SNMB), and the Walker Lane shear zone (Atwater & Stock, 1998;Benz et al., 1992;Thurber et al., 2009). The Sierra Nevada mountain range mainly comprises metamorphic sedimentary and volcanic rocks in the SNMB and intrusive granitic rocks in the SNB (Irwin & Wallace, 1990), both of which were formed during past subduction processes. The Walker Lane is a relatively young transform/transtensional fault system as compared to the San Andreas Fault (SAF) to the west and is marked by NW-striking dextral strike-slip faults, Sierran range front normal faults, and a few left-lateral faults between the NW moving Sierra Nevada and E-W extending Basin and Range (Wesnousky, 2005). It has been suggested that the foundering of the eastern Sierran lithospheric mantle and/or crustal root in the Neogene period leads to convective mantle upwelling which is responsible for the crustal thinning, uplift of the Sierran range, and formation of young volcanism such as the Long Valley Caldera (LVC)