STRATIGRAPHIC AND TEMPORAL ARCHITECTURE OF A SUPRADETACHMENT BASIN: CENTRAL MOJAVE METAMORPHIC CORE COMPLEX

The coarse-grained Pickhandle Fm. and overlying fine-grained Barstow Fm. in the central Mojave Desert comprise a >2 km thick section of intercalated volcanic, volcaniclastic, and epiclastic rocks. This section had previously been interpreted to represent syn- and post-kinematic, respectively, hangingwall basin fill that accumulated in the hangingwall of the Central Mojave Metamorphic Core Complex. They characterize a fundamental assumption in past basin analyses of supradetachment basins; grain-size is reflective of tectonic environment. Yet, no studies have clearly established definitive links in space and time between a basin's sedimentation history and the tectonic slip of its bounding fault. Our ongoing 40Ar/39Ar geochronology and thermochronology, and geologic mapping investigation documents, in detail, the lateral and vertical variation in the distribution of lithofacies in time and how it relates directly to the timing and magnitude of slip on the bounding fault.

New age dates from the Pickhandle Fm. suggests the onset of deposition youngs from north to south beginning ~21.5 Ma in the Gravel Hills to ~19.3 Ma in the northern Calico Mts. In the Gravel Hills the Pickhandle Fm. is dominantly volcanic and volcaniclastic, strikes E-W and dips 45° south and is unconformably overlain by 17.7 Ma basalt flow, which is intern overlain by a thick plutoniclastic boulder conglomerate section that strikes N20W and dip 15° SW. While in the southern Calico Mts., and southern Mitchel Range lacustrine deposition dominated from ~19-17 Ma (Singleton and Gans, 2005; Van Pelt and Gans, this volume).

Preliminary age constraints on the timing of footwall uplift suggest slip on the detachment began ~20 Ma and continued until at least 17.5 Ma (Gans et al., 2005), broadly coeval with lacustrine deposition in the southern hanging wall region and tectonic tilting and erosion to the north. We anticipate additional thermochronology from the footwall and geochronology from upper plate basins will illuminate the links between the tectonic history of the basal detachment fault and the stratigraphic and temporal architecture of the hangingwall basin.