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

晚中生代至古近纪的方济各杂岩、大峡谷群/海岸山脉蛇绿岩和加利福尼亚的内华达山脉岩基构成了古代安第斯式会聚板块边缘的经典例子。在加州中部，这些单元形成了一个简单的模式，但在南加州则被打乱了。此外，在南加州，弧复合体坐落在一个神秘的片岩上，根据一个明显的交叉火成岩体的年龄，它太老了，不可能是方济会或大峡谷序列的变质物，但从逻辑上讲，片岩应该与这些岩石中的一组有关。最近对片岩碎屑锆石的年代测定结果与白垩纪岩石的年代对比一致，表明该古老火成岩体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分配到正确的原岩序列中。解决这个长期存在的谜题将大大澄清和简化这一经典地区的收敛历史。

9902960BarthThe 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.