Late Cretaceous extensional unroofing in the Funeral Mountains metamorphic core complex, California

New field and geochronologic data document the existence of Late Cretaceous extensional structures in the Death Valley region, California-Nevada. Two major, low-angle, ductile shear zones have been mapped that omit stratigraphy in the footwall of the Funeral Mountains metamorphic core complex. Intervening strata have been strongly attenuated. Although stratigraphic offset across the shear zones is only 1.5km, the presence of a large metamorphic discontinuity suggests that the amount of unroofing must be much greater. The timing of shear-zone formation, attenuation, and subsequent northwest-vergent folding is constrained by U-Pb geochronology on 1) prekinematic or synkinematic, and 2) postkinematic pegmatites. Deformation was taking place by 72 Ma and had ended by 70 Ma. These results support earlier petrologic and geochronologic data that suggested substantial unroofing of the Funeral Mountains in Late Cretaceous time and add to a growing body of evidence for widespread Mesozoic extension in the hinterland of the Sevier thrust belt. -Authors