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

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