Exhumation history of the southern Black Mountains, California, with implications for extreme extension in the Death Valley area

Byrdie Renik

Department of Earth and Environmental Sciences, Columbia University, NY

[email protected]

The Death Valley area of California and Nevada has received particular attention in the effort to understand large-scale continental extension. The Black Mountains, located on the eastern edge of Death Valley, provide critical evidence for the amount and timing of tectonic exhumation, and at present are widely thought to have an extensional origin. Although extension in the area has undoubtedly been considerable and deeply influential on the modern Black Mountains, certain Neogene sediments predating significant extension lie in depositional contact with Cambrian rocks, suggesting substantial pre-extensional denudation. Existing thermochronological data do not cover much of the southern Black Mountains, an area featuring especially extensive exposure of the 1.7 Ga crystalline basement. The present study proposes to date the unroofing of that basement and the Proterozoic metasedimentary rocks overlying it via fission track, (U-Th)/He, and ⁴⁰Ar/ ³⁹Ar analysis, supported by mapping of associated structure. If the thermal history of the rocks shows cooling to low temperatures prior to Neogene time, it would indicate that the Black Mountains had begun exhumation before the main phase of extension, probably during Mesozoic shortening. This would imply that the amount of extensional unroofing is more moderate than generally thought.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid