HISTORY OF EXHUMATION AND RELATED STRUCTURAL RELIEF GENERATION FOR THE SOUTHERNMOST SIERRA NEVADA BATHOLITH, AND TECTONIC FORCING INTERPRETATIONS

The southernmost Sierra Nevada batholith (SSNB) preserves an oblique crustal section over its ~100 km strike length with southward increasing exposure depths from ~10 km to ~35 km. Cretaceous igneous construction of the deeper southern ~50 km of the section was completed by high-flux additions of tonalitic magma in the west at ca. 100 Ma, and more modest granodioritic input to the east by ca. 90 Ma. Rapid structural ascent of the SSNB occurred in two phases immediately following igneous construction: 1) Oceanic plateau collision-related tectonic uplift and ensuing erosional denudation (ca. 100-90 Ma) from deep- to mid-crustal levels with the flooding of the trench by arc-derived clastic sediments. 2) Large magnitude SW-directed crustal extension (ca. 90-80 Ma) driven by eduction of deeply subducted clastic material following passage of the oceanic plateau. Mid-to-upper crustal detachment sheets constitute much of northern Salinia, and occur as isolated extensional nappes above the deepest level SSNB autochthon with 15-20 km of missing intervening crust. By no later than the K-T boundary the deeply denuded rocks were covered by marine supra-detachment strata of the Big Creek, Uvas, Witnet and Goler formations, nonconformably above both denuded detachment fault and extensional nappe remnants. Marine clastic sedimentation extended through Eocene time, and subsequent erosional re-denudation of much of the underlying basement progressed until the end of the Oligocene. During the early Miocene the SSNB was broken into a series of grabens and horsts with ~1 km-scale of structural relief, with basinal areas receiving up to 2 km of siliciclastic and volcanic strata that grade laterally westwards to marine strata of the San Joaquin basin. These relations resulted from passage of the Mendocino triple junction, with many of the high-angle normal faults reactivating Late Cretaceous basement structures. The lower Miocene strata were eroded off the SSNB basement as a result of complex epeirogenic movements forced by the break-off and tilting of the Sierran microplate and subsequent mantle lithosphere delamination. Long-wavelength topography of the southern Sierra Nevada range reflects the Late Cretaceous large magnitude extension, whereas short-wavelength topography reflects the Miocene high-angle normal faulting.