TRANSTENSIONAL FAULT PATTERNS OF THE WALKER LANE-EASTERN CALIFORNIA SHEAR ZONE, EASTERN MARGIN, SIERRA NEVADA MICROPLATE

Transtension is the primary structural mechanism governing active deformation at the eastern margin of the Sierra Nevada Microplate. Analysis of this corridor clarifies the role of transtensional kinematics in the formation of discrete, seemingly heterogeneous, structural provinces within the Walker Lane-Eastern California Shear Zone (WL-ECSZ). Fault types and patterns are determined by the dominance of the coaxial vs. noncoaxial component of strain, derived from the geometry of the deformation zone boundary (zb, eastern Sierra) and transport direction (TD, of the Microplate). Rotation and associated size reduction of fault blocks in transtension explains the observed westward encroachment of deformation in the eastern Sierra.

The map-view instantaneous strain patterns predicted are demonstrated from N-S by the observed active normal and wrench fault arrays. The Honey Lake-Pyramid Lake domain has zb striking 310° to 330°, and TD of ~298°, indicating noncoaxial strain dominance (Honey Lake, Warm Springs Faults), transitioning to coaxial dominance (Pyramid Lake, normal faults to the west). The Lake Tahoe region is coaxially dominated, as indicated by zb ~341° and TD of 303°. Predicted structures correspond to the Genoa, Donner Pass, and other mapped and inferred faults. The Mono Lake-Long Valley province has zb 330° and TD ~308°, indicating a coaxially dominated system that corresponds to numerous normal faults across both basins, at their margins, and along the Sierran rangefront. The Owens Valley-Fish Lake Valley region has zb oriented 344° and TD varies 310° to 314° from N-S, respectively. Faulting north of Bishop is dominantly coaxial, whereas faulting in the central and southern regions is dominantly noncoaxial as indicated by the change in TD. In Coso-China Lake, zb is oriented 344° and TD is 316°, indicating a dominantly coaxial system with predicted structures similar to observed faults (Wild Horse Mesa, Coso Wash, Airport Lake, Little Lake). Active fault patterns in these distinct provinces present a snapshot of instantaneous transtensional strain. Local partitioning, in response to zone boundary variation by the inherent shape of the Sierra Nevada and systematic rotation of its transport direction, explains the variation in dominant structural deformational styles along the length of the WL-ECSZ.