No abstract

Transtension in the upper crustal brittle field, at the lithospheric scale, involves some difficult kinematic problems that result from the non-coaxial component of bulk strain, which generates rotation about vertical axes and the internal deformation of rotating blocks. Plate boundary zone deformation in the non-plane-strain brittle field cannot involve the rotation of a mosaic of very large rigid crustal blocks. In transtension, constriction is achieved by simultaneous arrays of rotating normal faults and wrench faults, partitioned spatially and temporally, producing very complex polyphase brittle deformation. The Coso transtensional region at the southeastern margin of the Sierra Nevada-Great Valley block illustrates the complex synchroneity and polyphase superposition of rotating normal and wrench fault arrays in a constrictional strain field in the brittle regime, which generates a "continuum rubble" of small blocks.

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 LakePyramid 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.