Transtensional analyses of fault patterns and strain provinces of the Eastern California shear zone–Walker Lane on the eastern margin of the Sierra Nevada microplate, California and Nevada

Abstract

Obliquity of the strain velocity field to the deformation zone boundary requires strain to be triaxial. At the plate boundary scale, fault geometries predicted by transtensional theory better explain observed fault patterns in the northern Eastern California shear zone–Walker Lane area than do 2D plane strain predictions. Structural provinces in the Eastern California shear zone–Walker Lane are defined by variations in the orientation of the eastern margin of the Sierra Nevada microplate, and include the Honey Lake–Pyramid Lake, Lake Tahoe, Mono Lake–Long Valley, Owens Valley, and Coso subprovinces. The local geometry of the transtensional zone boundary and the microplate transport direction determines orientations of the instantaneous strain axes for each province. Fault orientations predicted with respect to these axes are consistent with those observed in each structural province. The variation of zone geometry among predominantly coaxially dominated strain provinces over a consistent period of deformation does not result in dramatic changes in shape or orientation among finite strain ellipsoids. Although Quaternary faulting strongly reflects transtensional kinematics, the magnitude of estimated finite strain for each province suggests that present-day transtensional deformation has not accommodated large amounts of extension, vertical thinning, or strike-slip offset. K-values for all structural provinces plot in the k>1 constrictional field on the logarithmic Flinn (Ramsay) diagram, indicating non-plane, transtensional strain. Collectively, these theoretical applications and structural–tectonic observations have implications for evaluating kinematics and faulting during brittle non-plane strain deformation, and for the overall evolution of the transtensional Sierra Nevada–North America plate boundary.