Forearc-basin sedimentary response to rapid Late Cretaceous batholith emplacement in the Peninsular Ranges of southern and Baja California

Abstract

The eastern Peninsular Ranges batholith is dominated by voluminous La Posta–type tonalite-granodiorite intrusions that compose half of the magmatic arc at present erosion level. Zircon U-Pb and hornblende 40 Ar/ 39 Ar results from these intrusions indicate that they were emplaced in a remarkably narrow interval (99–92 Ma) that closely followed cessation of west-directed compression of the arc system. Emplacement of the La Posta suite coincided with a major pulse of coarse-grained sediment into the adjacent forearc basin in early Cenomanian to middle Turonian time. Paleontologic control, and plutonic age and detrital zircon U-Pb data demonstrate the virtual absence of a time lag between magma emplacement and sedimentary response. The tight linkage between magmatism, arc exhumation, and sediment delivery to the forearc indicates that development of major erosional topography in the arc was driven by thermal and mechanical effects associated with large-volume batholith emplacement.