TECTONIC RECONSTRUCTION OF THE LAST CHANCE THRUST SYSTEM, DEATH VALLEY NATIONAL PARK, CALIFORNIA

The Last Chance thrust system of east-central California represents a period of Late Paleozoic deformation immediately preceding Triassic initiation of North American Cordilleran subduction. Contractional deformation along this margin was sporadic between the Late Devonian and Early Triassic, and the nature of individual events remains poorly constrained. Characterization of the Last Chance thrust and distinction from other Permian-Triassic structures is critical in refining the tectonic evolution of the southwestern margin of Laurentia. The Permian Last Chance thrust system is best exposed in the Last Chance Range of Death Valley National Park, California. The thrust has been heavily dissected by Cenozoic Basin and Range extension, and its current exposure is limited.

Determining the extent to which Cenozoic deformation has modified the original geometry of the Last Chance thrust is crucial in accurately reconstructing the thrust system. New geological mapping and balanced cross-section construction within the Last Chance Range reveal a greater contribution by late Cenozoic transtensional structures to thrust dissection than was previously recognized. Restoration of Basin and Range extension within the Last Chance Range, as well as across the White-Inyo Mountains-Death Valley Region, provide a view of the Last Chance system following thrust emplacement. The thrust cuts up-section in the Last Chance range, and with north-trending east-vergent folds and east-trending lineations, we interpret eastward transport of the thrust sheet. This geometry is consistent with secondary shortening structures within a southeast-trending sinistral strike-slip shear zone. The Last Chance thrust system formed as a transpressional feature along the southeast trending California-Coahuila transform. Continued transpression along this margin possibly led to subduction initiation during the late Permian-early Triassic.