RE-EVALUATING THE NEOPROTEROZOIC-CAMBRIAN TECTONIC HISTORY OF SOUTHWEST LAURENTIA

Tectonic models for the timing and nature of the breakup of the Neoproterozoic supercontinent Rodinia remain contentious, with major inconsistencies existing between paleogeographic reconstructions and the geologic records preserved along the southern and western margins of Laurentia. Paleogeographic reconstructions suggest that Laurentia had separated from adjacent conjugate continents by ~635 Ma. Many regional geologic studies, on the other hand, suggest that successful rifting and the development of passive margins along Laurentia’s southern and western margins occurred in the early Cambrian. Evaluating these divergent interpretations for the tectonic histories of Laurentia’s margins requires improvements to age models for Neoproterozoic-Cambrian rift-related tectonism, volcanism, and basin subsidence in southwestern Laurentia, which demand new geochronological constraints and better calibration of unconformities within these successions. To contribute towards addressing this problem, we present Tonian through Cambrian stratigraphic and U-Pb geochronology data from the Death Valley region (CA and NV) and Sonora, Mexico. The results of this work provide some of the first Cryogenian and Cambrian ages from a region that has been notoriously depauperate of radiometric age control. We discuss the tectonic implications of these ages and future directions for resolving the tectonic history of southwestern Laurentia.