DETRITAL ZIRCON GEOCHRONOLOGY AND GEOCHEMISTRY OF THE SOUTHERN CALIFORNIA CRETACEOUS FOREARC BASIN, SANTA YNEZ MOUNTAINS, CALIFORNIA

Forearc basins form at convergent margins due to subsidence between the subduction complex and the magmatic arc, and studying the provenance of sedimentary rocks within forearc basins can provide greater understanding of how subsidence within forearc basins is related to tectonic events in adjacent lithotectonic belts. In northern California, the evolution and provenance of latest Mesozoic forearc basin strata of the Great Valley Group of California are well documented. In contrast, due to latest Cretaceous convergent margin deformation and recent dextral transform displacement, the Cretaceous southern California forearc basin is not as well understood as its northern counterpart. However, recent detrital zircon data from the Nacimiento block exposed on the central California coast indicates a regional unconformity that ended in the Albian and coincided with the arrival of a unique zircon population with ages and geochemistry suggesting derivation from juvenile Jurassic igneous rocks. We will present new detrital zircon geochronology and geochemistry from samples of the Espada and Jalama formations from the Santa Ynez mountains, and which represent the continuation of the Nacimiento block Cretaceous forearc basin in southern California. We will use detrital zircon ages to estimates the age of the strata, and zircon geochemistry to assess their provenance. This data can be compared to results from the Nacimiento block to assess the regional nature of the middle Cretaceous unconformity and the source of juvenile zircon within the Cretaceous forearc.