CONSTRAINING THE NEOGENE DISPLACEMENT OF THE DEATH VALLEY EXTENSIONAL SYSTEM, CALIFORNIA, USING THE MESOZOIC TECTONIC HISTORY OF THE HANGING WALL BLOCK

The Death Valley extensional system (DVES) is considered to be a world-class example of a modern extensional system but there is no consensus of the amount of extension, with estimates from 20 to 100 km. New mapping, structural, and geochronological data on the Mesozoic tectonic history for the immediate hanging wall of the DVES yields features that constrain the displacement of the DVES.

Linking the hanging wall (Panamint Range) to the footwall (Black Mountains) of the DVES requires detailed knowledge of geologic features to use as restoration markers. Data from the Panamint Range provide a unified tectonic polyphase history with distinct spatial relationships: (1) Jurassic contractional and extensional deformations and dike swarm, volcanic rocks, and large plutons in the south with higher-grade deformation along the western edge; (2) a steep rim syncline to a large plutonic body in the south; (3) middle Cretaceous normal and strike slip fault system in the south; and (4) Late Cretaceous contractional and extensional deformation with relatively small plutons along the western and northern sides.

There are no known Miocene age piercing points to palinspastically restore 16—0 Ma slip of the DVES, so the next best feature to would be from the next older event, which was NNW-directed extension at ~70 Ma. Late Cretaceous dikes and fabrics they crosscut are known in the footwall of the DVES and along the western edge of the Panamint Range. This deformation zone yields a linear restoration marker instead of a point. The total displacement vector of the DVES consists of two extension events, earlier top-to-the-WSW followed by a more rapid NNW-directed. The total displacement vector is NW-trending, because the largest pulse of extension and exhumation occurs during NNW-directed extension, resulting in a longer NNW-directed hanging wall displacement vector. Using the Pavlis and Trullenque (2021) slip vector for the Southern Death Valley fault as the NNW-vector and an inferred 10—20 km of WSW directed slip of the earlier extension places the western Black Mountains underneath the Wildrose area of the northwestern Panamint Range for a total displacement of ~50 km. This hypothesis needs further testing and refinement by looking for and examining many other features.