GEOCHRONOLOGIC, THERMOBAROMETRIC, AND ISOTOPIC CONSTRAINTS ON THE ORIGIN OF THE SALINIAN BLOCK

Granitic and metamorphic basement rocks of the Salinian block (central coastal California) are widely regarded to have originated from southern California, prior to displacement ~310 km northward along the San Andreas fault system since ca. 28 Ma. Less clear are the original positions of individual components of the Salinian block prior to a major Late Cretaceous extensional episode that affected the Mojave Desert, the southern Sierra Nevada, and Salinia. We compile new and existing lithologic, U-Pb geochronologic, thermobarometric, and isotopic data with the goal of constraining the native site of the Santa Lucia Range (central Salinia). Aluminum-in- hornblende and garnet-aluminosilicate (sillimanite)-silica- plagioclase geobarometry indicate that emplacement and metamorphic pressures do not vary significantly across the range, with values diminishing slightly from ~7.5 kbar in the Coast Ridge belt to ~6 kbar in the Central block. These results indicate that the entire Santa Lucia Range represents a mid-to- deep crustal (~20-25 km paleodepths) exposure through the Salinian arc. Pluton emplacement ages and zircon Hf isotopic values vary from west to east in the Salinian arc from ca. 102 to 82 Ma and +1 to -9, respectively. Pre-intrusive “Sur Series” metamorphic framework assemblages show a similar range of lithologies (including chiefly metasandstone, metapelite, and marble) and U-Pb detrital zircon age spectra (peaks at ca. 0.25, 1.1, 1.4, and 1.8 Ga) to Paleozoic to Mesozoic inner shelf miogeoclinal rocks in Death Valley, the Mojave Desert, and the Snow Lake terrane. In aggregate, the data presented here are most compatible with basement rocks of the Santa Lucia Range originating from the modern-day location of Tehachapi Valley. In each location, inner shelf miogeoclinal rocks host ~6-7 kbar intermediate plutons with overlapping ages and isotopic values. After forming, the Santa Lucia Range must have detached from footwall rocks of the southern Sierra Nevada and been displaced ~75 km to the SSW. This magnitude of displacement and the scale of the dismembered southern Sierra- Mojave-Salinia regional core complex rival those of the largest metamorphic core complexes exposed in the North American Cordillera.