Transtension in the Brittle Field: The Coso Region, Southern California

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.