LATE CRETACEOUS COOLING OF THE EAST-CENTRAL PENINSULAR RANGES BATHOLITH (33°N): RELATIONSHIP TO PLUTON EMPLACEMENT, SHALLOW SUBDUCTION, AND FOREARC SEDIMENTATION

Based upon integrated U-Pb and K-Ar data from the basement and forearc of the Peninsular Ranges batholith (PRB) near 33˚N, we have customized numerical models to evaluate competing hypotheses for two distinct phases of Late Cretaceous rapid cooling that affected this segment of the convergent margin. The 2-dimensional finite difference models simulate overlapping intrusion, denudation, and/or subduction effects. Cooling at 91-86 Ma seems clearly related to denudation resulting from emplacement of the voluminous suite of 96 ± 3 Ma La Posta plutons. In contrast, cooling after 78 Ma could be related to either erosional denudation or subduction refrigeration during Laramide shallow subduction beneath the PRB. While our numerical simulations indicate that later cooling phase can be explained by both processes, the final erosion depths predicted by the two models differ significantly (up to 20 km for pure erosional denudation but only to 11 km for subduction refrigeration followed by erosion). Both results are within the range indicated by independent thermobarometry of the eastern batholith. Based upon the similarity of independently determined denudation histories from PRB basement rocks and forearc sediments that onlap the northern PRB, we conclude that erosional denudation was probably the most important process between 78-68 Ma. We speculate that removal of lower crust and lithospheric mantle beneath the east-central during Laramide shallow subduction triggered erosional denudation and localized thrusting until the density balance between the crust and mantle was restored in latest Cretaceous-early Tertiary time.