TECTONIC EVOLUTION OF THE CENTRAL DEATH VALLEY RHOMBOCHASM, SOUTHEASTERN CALIFORNIA

The central Death Valley rhombochasm, of southeastern California, is a 65-by-80-km rhombic pull-apart basin-complex which formed in the releasing step-over between two major northwest-striking right-lateral strike-slip faults: The northern Death Valley—Furnace Creek and southern Death Valley faults. Stewart (1983) demonstrated this feature by correlating a disjointed array of thrust fault segments, facies, and isopachs, which were offset by basin-range transtension, and which palinspastically restore in unison when the rhombochasm closes. Only the westernmost part of the rhombochasm is still tectonically active and is a basin that corresponds to the central part of Death Valley—Badwater basin. Whereas the geometry of the rhombochasm has changed greatly during its evolution, the current active structure is still a rhombic pull-apart basin in the same releasing step-over between the same two strike-slip faults.

The basin-fill of the rhombochasm consists of four distinct allostratigraphic units formed in four successive regional stages of basin-range tectonism. Each of these four tectonic stages is distinct in its characteristic strain regime and pattern of extension-related magmatism. In the first two stages, from ≈14.5 to ≈12 and from ≈12 to ≈7 Ma, the rhombochasm was a supradetachment basin, floored by a metamorphic-intrusive core complex. In the two remaining stages, from ≈7 to ≈4 Ma and from ≈4 Ma to present, progressively higher-angle faults have cut across the abandoned detachment fault, forming numerous smaller basins that are nested within the original detachment-floored area of the rhombochasm, including Badwater basin. Tectonic dissection related to these younger crosscutting basins provides unparalleled exposures of both the upper and lower plates of the early supradetachment basin.

The tectonic evolution of the rhombochasm is presented in a series of sequential palinspastic reconstructions, in both map view and cross sections. It is particularly notable that detachment faulting, although very important in the evolution of the rhombochasm, has been neither a defining nor an enduring feature of it. Moreover, the initial formation of the detachment fault was evidently a separate, larger-scale event that at least slightly predated the formation of the rhombochasm along it.