ABSTRACT: Origin of the Late Cretaceous Salinian Basin by Partitioning of the California Batholith
GROVE, KAREN, San Francisco State University, San Francisco, CA
A thick succession of Upper Cretaceous bathyal marine to nonmarine strata exposed on the Salinian terrane, located west of the San Andreas fault in central California, records basin formation within an uplifted magmatic arc complex. Campanian crystallization ages for Salinian plutonic rocks show that uplift was rapid prior to deposition of overlying Maastrichtian sedimentary strata. The Salinian basin may have formed as an east-west-trending intra-arc graben that partitioned the California batholith into a northern Sierran section where subduction was oblique, and a southern Peninsular section where subduction was more orthogonal. A modern analog is the Sunda Strait, a zone of extension between the islands of Sumatra and Java, that accommodates the transition from oblique to orthogona subduction. The Salinian basin formed following a period of plate reorganization, when the Kula plate was born, and the subducting Farallon plate accelerated and shoaled to produce eastward migration of the magmatic arc and compression across the western margin of North America. Westward thrusting and clockwise rotation of the southern Sierran batholith also may have been involved in basin formation. The intra-arc model explains deposition of forearc deposits on Salinian batholithic rocks similar to eastern Sierran plutons, and differences between Upper Cretaceous Salinian fore-arc-type deposits and Sierran (Great Valley) and Peninsular forearc deposits. Subsidence continued within the Salinian basin until the Paleogene, when deposition was disrupted by uplift and erosion.