DATING THE FORMATION AND EXHUMATION OF THE COAST RANGE OPHIOLITE AT POINT SAL

Models for the formation of the Coast Range Ophiolite include near-shore east-dipping subduction initiation, supra-subduction zone initiation well off-board the margin, and a far-traveled mid-ocean ridge origin. These models make predictions for the age and early exhumation history of the Coast Range Ophiolite, which we test with new geochronologic and thermochronologic constraints. We report new zircon U-Pb geochronology, and zircon and apatite (U-Th)/He thermochronology on gabbro from the Coast Range Ophiolite and ashes in the overlying chert-dominated cover sequence at Point Sal, along the Central California coast. Ashes within the cover sequence bracket conglomeratic horizons with clasts of gabbro, suggesting that they date an episode of local exhumation. By comparing U-Pb zircon dates from these ashes to those from the underlying gabbro, we can better constrain the timing between formation and obduction of the Point Sal Ophiolite. We will then compare these data with the first evidence for detritus derived from continental North America in the cover sequence, to further constrain the regional tectonic history. Additionally, gabbro clasts are present in the Eocene to Miocene Sespe and Lospe Formations. Thermochronology can be used to refine the age of later exhumation of the ophiolite, potentially associated with ridge-trench interaction in the Neogene.