TECTONIC AND MAGMATIC EVOLUTION OF THE CENTRAL DEATH VALLEY RHOMBOCHASM, INYO COUNTY, CALIFORNIA

We present a series of palinspastic maps and cross sections illustrating the tectonic and magmatic evolution of the central Death Valley rhombochasm–a pull-apart basin-complex that has formed in the releasing, 65-km (N-S) step-over between two NW-striking right-lateral strike-slip faults: the Furnace Creek and southern Death Valley faults. J.H. Stewart (1983, Geol.; 11; 153-157) first demonstrated the rhombochasm’s existence by proving that the Panamint Range upper-plate block has been extensionally transported ≈80 km northwestward of the Resting Spring Range lower-plate block creating, in between, a supradetachment pull-apart basin underlain by a core complex of 1.7-Ga gneisses and lateTertiary plutons.

We have refined Stewart’s model by detailed analysis of the stratigraphy and structure of the rhombochasm and the surrounding region. The basin-fill consists of four distinct stratigraphic units: (1) Funeral Formation and overlying, syntectonic Quaternary deposits (≈4.5 Ma to present), (2) Furnace Creek Formation (≈7.5 to ≈3.0 Ma), (3) Artists Drive Formation (≈12.5 to ≈7 Ma), and (4) strata of the Billie Mine area (≈14.5 to ≈11.5 Ma). These four units are separated by unconformities that young to the northwest, across which profound abrupt changes are present in lithology, provenance, facies patterns, and distributions. All but the oldest of the four basin-fill units contain abundant clasts derived from the preceding units, and clasts of the core-complex rocks are locally abundant in the two younger units. Thus, tectonic events that occurred during evolution of the rhombochasm resulted in repeated structural disruption of the basin-fill and basin floor. Further, the relationships between faults that are internal to the rhombochasm and features of the basin fill, such as facies patterns, record a complex, multi-stage history. Four tectonic stages of development are each characterized by a distinct strain regime and a distinct style of intrabasin volcanism. Detachment faulting was only involved in the first two stages of evolution, from ≈14.5 to ≈7 Ma. Since then, this rhombochasm has continued to evolve by development of a series of nested basins with first, moderate- and then, high-angle master faults that have cut across and thus dismembered the Amargosa detachment fault—the original basin floor.