Thermal evolution and exhumation of deep-level batholithic exposures, southernmost Sierra Nevada, California

The Tehachapi complex lies at the southern end of the Sierra Nevada batholith adjacent to the Neogene-Quaternary Garlock fault. The complex is composed principally of high-pressure (8–10 kbar) Cretaceous batholithic rocks, and it represents the deepest exposed levels of a continuous oblique crustal section through the southern Sierra Nevada batholith. Over the southern ~100 km of this section, structural/petrologic continuity and geochronological data indicate that ≥35 km of felsic to intermediatecomposition crust was generated by copious arc magmatism primarily between 105 and 99 Ma. In the Tehachapi complex, these batholithic rocks intrude and are bounded to the west by similar-composition gneissic-textured high-pressure batholithic rocks emplaced at ca. 115–110 Ma. This lower crustal complex is bounded below by a regional thrust system, which in Late Cretaceous time tectonically eroded the underlying mantle lithosphere, and in series displaced and underplated the Rand Schist subduction assemblage by low-angle slip from the outboard Franciscan trench. Geophysical and mantle xenolith studies indicate that the remnants of this shallow subduction thrust descend northward through the crust and into the mantle, leaving the mantle lithosphere intact beneath the greater Sierra Nevada batholith. This north-dipping regional structure records an infl ection in the Farallon plate, which was segmented into a shallow subduction trajectory to the south and a normal steeper trajectory to the north. We combine new and published data from a broad spectrum of thermochronometers that together form a coherent data array constraining the thermal evolution of the complex. Integration of these data with published thermobarometric and petrogenetic data also constrains the tectonically driven decompression and exhumation history of the complex. The timing of arc magmatic construction of the complex, as denoted above, is resolved by a large body of U/Pb zircon ages. High-confi dence thermochronometric data track a single retrogressing path commencing from widely established solidus conditions at ca. 100 Ma, and traversing through timetemperature space as follows: (1) Sm/Nd garnet ~770–680 °C at ca. 102–95 Ma, (2) U/Pb titanite 40 Saleeby et al. spe 419-02 28 pages