Collaborative Research: Age and Correlation of the Protolith of the Pelona-Orocopia-Rand Schist: Implications for Cordilleran Late Mesozoic-Early Tertiary Tectonics

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9902788Jacobson The late Mesozoic to Paleogene Franciscan Complex, Great Valley Group/Coast Ranges ophiolite, and the Sierra Nevada batholith of California comprise on of the classic examples of an ancient, Andean-style convergent plate margin. In central California these units define a simple pattern, but are disrupted in southern California. Additionally, in southern California, the arc complex sits on an enigmatic schist that, based on the age of an apparently cross-cutting igneous body, is too old to be the metamorphosed equivalent of either the Franciscan or the Great Valley sequence, yet it is logical that the schist should correlate with one of these sets of rocks. Recent dating of detrital zircons from the schist has produced ages compatible with correlation to the Cretaceous rocks, leading to the possibility that the old igneous body is an inclusion or tectonic pebble in the schist rather than crosscutting the schist. This project will persue additional detrital zircon studies of the schist fragments of this system in order to confirm its age and to assign it to the correct protolith sequence. Resolution of this long-standing enigma will greatly clarify and simplify the convergent history of this classic area.