Footwall structural evolution of the Tucki Mountain detachment system, Death Valley region, southeastern California

Tucki Mountain lies within the central portion of the Death Valley extended terrain. Its structure is dominated by the Cenozoic Tucki Mountain detachment system, a complex and long-lived extensional feature which places weakly metamorphosed-unmetamorphosed strata on middle to upper greenschist facies metamorphic rocks. Detailed analysis of tectonites in the footwall of the detachment system has led to the identification of seven phases of ductile structures. The earliest are latest Mesozoic-earliest Tertiary(?) isoclinal folds and associated schistosity which may have been related to compressional deformation. All subsequent generations of structures developed during Cenozoic extension at intermediate-upper crustal levels. Structures of D ₃ and D ₅ age are markedly asymmetric and record simple-shear deformation along the detachment system. Kinematic analysis of these structures indicates consistent NNW movement of the hanging wall relative to the footwall throughout the history of the fault zone. This extension direction is inconsistent with the overall N45W-S45E direction indicated for the Death Valley region by the orientation of major transfer faults like the Death Valley and Furnace Creek fault zones. The discrepancy may reflect late-stage changes in the regional extension direction from N-S to NW-SE, or a partitioning of overall NW-SE extension into domains of variably orientated local extension.