DECIPHERING THE POLYPHASE TECTONIC EVOLUTION OF THE JURASSIC-CRETACEOUS ARC IN THE DEATH VALLEY REGION BY REVISITING THE ENIGMATIC BUTTE VALLEY FAULT, PANAMINT RANGE, CALIFORNIA

The Butte Valley fault is an anomalous Mesozoic structure in the Death Valley region of California. Numerous aspects of this structure are odd: a different transport direction than other Jurassic thrusts, a paucity of subsidiary structures, not exposed anywhere, and strike-trace that has been bent over 135˚.

A new study via detailed geologic mapping, structural analysis, and CA-TIMS U-Pb zircon geochronology reinvestigates this structure to test alternative interpretations and to match to other regional structures. The apparent uniqueness of this fault may make it an important marker for restoration of subsequent tectonic displacements allowing paleoreconstruction of the Mesozoic arc and Neoproterozoic glacial-tectonic strata and insight on Miocene to Recent displacement of the Death Valley transtensional system.

Mapping and structural analysis data reveal important differences from previous interpretations, most importantly is that the fault is well exposed. A previously interpreted intrusive contact of Paleozoic rock with quartz diorite in Warm Spring Canyon is a fault contact and in Butte Valley the fault is exposed cutting the Manly Peak quartz monzonite. These two segments have different kinematics but similar timing, style and paleostress axes. The Warm Spring Canyon segment is a left-lateral fault and the Butte Valley segment is a normal fault. Abundant small-scale structures and textures in the rocks adjacent to the Butte Valley fault record two other earlier deformations with hanging wall transport to the NE and to the west. The entire intrusive contact rim of the Manly Peak quartz monzonite has steep inward dipping bedding. The southern continuation of the Butte Valley fault has a deflection of strike and dip along a zone of Cretaceous top-to-the-east thrusting.

Geochronology data combined with relative timing observations show that the Butte Valley fault was active between 144 and 90 Ma, overprinted Jurassic thrust faulting and latest Jurassic top-westward extensional faulting, and is overprinted by Late Cretaceous thrust faulting. The style, timing and kinematics of this fault system match with the Kokoweef-South fault system exposed >100 km away at Mountain Pass, California. This location also has similar age Mesozoic plutonic rocks along with Jurassic and Late Cretaceous thrust faults.