Annual meeting, GSA, fall 1996

Synthesis of published mapping and geochronology, combined with reconnaissance bedrock mapping along the Deep Springs Fault Zone (DSFZ), suggests that active extensional faulting in the White-Inyo Mountains will eventually expose a metamorphic core complex.

Two lines of evidence suggest 10-12.6 km of extension directed N10W-N20W with about 2.5 km of vertical separation. Contact metamorphic zones along Birch Creek and east of Deep Springs Lake restore above each other, making preintrusion geometry more closely resemble other local plutons. The Poleta folds (from west to east an anticline, syncline, syncline, and anticline) restore above a similar sequence deeper in the stratigraphic section between Deep Springs Lake and Waucobi Embayment. This reconstruction requires a 10 degree fault dip, with extension paralleling regional strike slip faults.

Footwall rocks along the DSFZ are developing a planar tectonic fabric of closely spaced, polished surfaces and sheared lenses of rock The average fabric planes dip 42 degrees toward N36W (n=84). Overall domal form of the footwall resembles turtlebacks in Death Valley.

Deep Springs Valley is still actively subsiding, with syntectonic deposits not yet exposed. Regional volcanic rocks date from less than 4 Ma, marking a reasonable bound for the onset of extension and a 2.5 mm/yr lower limit for normal fault extension. Extension beginning 2 Ma requires a 5 mm/yr extension rate, similar to models for local strike-slip faults and suggesting integrated extension on normal and transform faults. Our classic concept of high-angle Basin Range faulting may actually apply to surficial faulting during metamorphic core complex formation.

Last Update: 08/25/96