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

9902788雅各布森晚中生代至古近纪方济会杂岩、大山谷群/海岸山脉蛇绿岩和加利福尼亚州内华达山脉岩基构成了古老的安第斯风格会聚板块边缘的经典例子。在加利福尼亚州中部，这些单位定义了一个简单的模式，但在南加州却被打乱了。此外，在加利福尼亚州南部，弧形杂岩位于一块神秘的片岩上，根据一个明显横贯的火成岩的年龄，太老了，不可能是方济各会或大山谷序列的变质对应物，然而，片岩应该与这些岩石中的一组相关联是合乎逻辑的。最近对片岩中碎屑锆石的测年结果与白垩纪岩石的对比结果相吻合，这导致了古老的火成岩可能是片岩中的包裹体或构造卵石，而不是横切片岩。该项目将对该系统的片岩碎片进行更多的碎屑锆石研究，以确定其年龄并将其归属于正确的原岩序列。这个长期存在的谜团的解开将极大地澄清和简化这一经典领域的汇聚历史。

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.