PLUTON PINNING OF AN ACTIVE MIOCENE DETACHMENT FAULT SYSTEM, EASTERN MOJAVE DESERT, CALIFORNIA

The Miocene Kingston Range-Halloran Hills detachment fault system of t he eastern Mojave Desert, California, delineates part of the eastern b reakaway zone for a profoundly extended area between the Sierra Nevada and the Spring Mountains structural blocks. The shallow-dipping, west -rooting detachment fault cuts discordantly across Paleozoic and Preca mbrian units in the Mesozoic foreland fold-and-thrust belt, exhibits w est- to southwest-trending corrugations with structural relief of up t o 1.5 km, and underlies the terrestrial Shadow Valley basin. Middle Mi ocene fault displacement and syntectonic sedimentation in the northern basin were terminated at approximately 12.4 Ma by intrusion of the la rge (approximately 130 km2), shallow-level (less-than-or-equal-to 4 km depth) Kingston Peak pluton across the detachment fault soon after fa ulting began. Basin sedimentation and fault displacement southeast of the pluton were not, however, disrupted by its emplacement and continu ed to evolve. Northern ''pluton-pinned'' and southern ''pluton-free'' domains were separated by the Blacksmith Hills fault, a northeast-stri king, right-slip lateral ramp that accommodated more than 3 km of post pluton differential extension between pinned and nonpinned domains. In more western regions, late phases of detachment-fault-related extensi on beneath formerly pinned areas (including western and central parts of the pluton itself) are believed to have led to the development of t wo generations of east-striking left-slip faults. Collectively, these dextral and sinistral transfer faults illustrate the complex patterns of differential extension and accommodation that can characterize deta chment-fault systems as adjacent areal domains of extension are genera ted and die.