SUBDUCTION COMPLEX UPLIFT AND EXHUMATION AND ITS INFLUENCE ON FOREARC STRATIGRAPHY IN THE GREAT VALLEY BASIN, NORTHERN SAN JOAQUIN VALLEY, CALIFORNIA

New seismic-reflection data from the northern San Joaquin Valley (Great Valley forearc basin), California, provide the first evidence of emergence and erosion of the Franciscan subduction complex during the Mesozoic. The degree of Cretaceous-age erosion of the subduction complex is a fundamental parameter necessary to understand the enigmatic process of blueschist exhumation. The concept of erosionally-driven exhumation previously seemed unsupportable due to a lack of documented Franciscan-derived sediment. However, our data document a wedge of sediment derived from the accretionary wedge that was deposited during the same period that Franciscan blueschists were uplifted from 20 to 3 km depth. Syn-tectonic growth strata in the Great Valley forearc basin record an early Maastrichtian phase of deformation, which elevated the subduction complex above sea-level. Once exposed, erosion generated a supply of sediment that prograded eastward (arcward) into bathyal waters of the forearc basin. The thickness and extent of these subduction complex-derived sediments argue for an areally extensive landmass located west of the forearc basin. Regional emergence of the subduction complex suggests that erosion served as a significant driver in the exhumation of Franciscan blueschists. Uplift of the subduction complex affected forearc stratigraphy. This uplift created a ponded forearc trough and shifted the locus of coarse-grained deep-water sediments eastward. The heights of clinoforms built from the margins of this trough indicate middle-bathyal water depths. This trough narrowed as sediments prograded from both the Sierran arc and Franciscan subduction complex. By latest Cretaceous time, a delta-slope-submarine fan system prograded from north to south down the axis of the forearc, filling it to shelfal water depths. Fundamentally, uplift and emergence of the subduction complex resulted in shoaling of the outer forearc, an eastward shift in the basinal depocenter, and a reordering of the sediment dispersal system to include multiple source terranes.