Structural and Geochronological Investigations of Neoproterozoic Rifting in Southwestern Laurentia

California Institute Of Technology, Pasadena CA

Investigators

Abstract

EAR-0107123 Wernicke The Cambrian explosion and its Neoproterozoic precursors occurred in a context of extraordinary environmental perturbations, including extreme fluctuations between warm and cold climate, possible True Polar Wander, at least one significant impact event, and the reorganization and eventual breakup of a supercontinent. The tectonic events may have been a primary cause of both climatic and polar wander events. Despite significant progress over the last decade, the lack of absolute age control on key successions has severely limited developing reliable global correlations and a chronology of rifting and continental plate motions on a par with the Phanerozoic. For this project, the investigators are obtaining U/Pb ages of authigenic xenotime overgrowths on detrital zircons, as well as standard U/Pb dating on detrital zircons, on sandstones from the relatively complete Neoproterozoic succession in southwestern Laurentia (Kingston and Panamint Ranges, southern California). This succession contains a rich record of multiple rifting events and subsequent passive margin subsidence, interspersed with a record of glaciations and subsequent warming events, incisions, and a possible impact event. The investigators have sampled key areas that contain a number of structural and stratigraphic constraints on the relative timing of rifting and glaciation, and are testing a recent hypothesis that a particular sandstone horizon in the passive margin sequence contains detritus derived from the Acraman impact structure, which would provide a key time-correlative horizon between East Gondwana and Laurentia, and suggest proximity of southern Australia and southwestern Laurentia during subsidence.