EXHUMATION AND ACTIVE TRANSTENSIONAL DISPLACEMENT TRANSFER IN THE CENTRAL WALKER LANE STRIKE-SLIP FAULT SYSTEM, WESTERN GREAT BASIN

Displacement between the Sierra Nevada and western Great Basin is accommodated by a belt of transtensional deformation constituting the northern Eastern California Shear Zone and Walker Lane. The internal architecture of the belt is controlled by pre-Cenozoic structures reactivated during northwesterly migration of the Sierra Nevada in the late Tertiary and Quaternary. Displacements within the north-northeast trending Eastern California Shear Zone and northwest-trending Walker Lane are connected by a 100 km wide, east-northeast trending structural stepover characterized by kinematically linked extensional and strike-slip faults. During the late Miocene and Pliocene, at least 50 km of dextral displacement was transferred across the stepover from the Furnace Creek fault system in California to transcurrent faults of the Walker Lane. Displacement transfer was accomplished by motion on a shallowly northwest-dipping basal decollement underlying the stepover. Upper greenschist to amphibolite facies metamorphic tectonites were exhumed in the cores of northwest-trending turtleback structures formed as the lower-plate was extracted from beneath an upper-plate composed of lower Paleozoic sedimentary rocks and upper Cenozoic pre-extensional and syn-extensional volcanic and volcaniclastic rocks. In the late Pliocene, the metamorphic turtlebacks were abandoned as displacement migrated to the northwest and as the stepover broadened to include the Owens Valley fault system bordering the southeastern Sierra Nevada. Today, upper-plate deformation is accommodated by a kinematically coordinated system of curvilinear faults and transtensional basins. The faults are underlain by a northwest-dipping decollement inferred from the progressive increase of earthquake hypocenter depths northwesterly across the active stepover. Fault-slip inversion and earthquake focal mechanisms record sinistral-, dextral-, and dip-slip motion on the curved fault array and together with a regional GPS velocity field indicate a complex pattern of constrictional strain. Strain associated with motion between tectonic blocks formed within the boundary zone separating the Sierra Nevada and western Great Basin as the northwesterly increasing regional velocity field interacted with pre-existing crustal structures.