Superposition of two kinematically distinct extensional phases in southern Death Valley: Implications for extensional tectonics

Geologic mapping in southern Death Valley, California, demonstrates Mesozoic contractional structures overprinted by two phases of Neogene extension and contemporaneous strike-slip deformation. The folding is most evident the middle unit Noonday Formation, these folds are cut a complex array faults. oldest identified faults primarily displace Neoproterozoic units as young Johnnie Formation. However, northernmost portion map area, they rocks Stirling Quartzite. Such seen northern Ibex Hills con­sist currently low- to moderate-angle, E-NE– dipping normal faults, which folded about SW-NE–trending axis. We interpret low-angle product an early, NE-SW related kinematically similar deformation recognized south study area. postdates at least some extension, indicating component syn-exten­sional shortening that probably related. Approximately EW-striking sinistral mapped Saddlepeak Hills. incompatible with suggesting younger, NW-SE Valley region. Other area include NW- NE-striking, high-angle crosscut Also, major N-S–striking, oblique-slip fault bounds eastern flank slickenlines showing rakes <30°, together pattern, suggests dextral-oblique movement along east front range. exact timing faulting hampered lack geochronology based on relationships, we find older extensional phase predates angular unconformity between volcanic and/or sedimentary succession assumed be 12–14 Ma correlations dated Owlshead Mountains overlying rock-avalanche deposits associated correlate Amargosa Chaos north, 11–10 Ma. mechanism behind Hills, including angle not entirely clear. transcurrent systems have been proposed explain extension-parallel many terranes, geometry consistent models. Collectively, field data support old hypothesis Troxel et al. (1992) early period SW-NE prominent younger has well documented just north Black Mountains, but potential role this earlier unknown given complexity In any case, recognition up-dip position detachment system indicates important questions remain how should reconstructed. our observations provide insight into stratigraphy Pass basin its relationship history It also highlights transitioned from transtension.