Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada

The South Virgin Mountains and Grand Wash trough comprise a mid-Miocene nor mal fault system that defines the boundary between the unextended Colorado Plateau to the east and highly extended crust of the central Basin and Rang e province to the west, In the upper 3 km of the crust, the system develope d in subhorizontal cratonic strata in the foreland of the Cordilleran fold and thrust system. The rugged topography and lack of vegetation of the area afford exceptional three-dimensional exposures. Compact stratigraphy and w ell-defined prefaulting configuration of the rocks permitted a detailed rec onstruction of the system. Reconstruction of cross sections based on more t han 300 km(2) of detailed mapping at a scale of 1:12000 shows that the faul t system accommodated more than 15 km of roughly east-west-directed Miocene extension. Extension was initially accommodated on moderately to steeply d ipping listric normal faults. As the early faults and fault blocks tilted, steeply to moderately dipping faults initiated within the fault blocks, sol ing into the early faults. Some of the early faults were active at dips of <20 degrees, Isostatically driven tilting is superimposed on tilting due to active slip and domino-style rotation of the fault blocks. Collectively th ese processes rotated originally steeply dipping faults to horizontal orien tations. The kinematics are inconsistent with the widely accepted view that many near-horizontal normal faults were rotated to their present orientati ons by later, crosscutting normal faults. However, re-examination of other areas suggests that the evolutionary sequence seen in the South Virgin Moun tains may, in fact, be widely applicable.