Petrography, Geochemistry and Isotopic Analysis of Paleogene Volcanism in the Fish Creek Mountains, Great Basin, North-Central Nevada

The Fish Creek Mountains, located in north-central Nevada, is a site of multiple igneous events ranging from 3 5Ma to 1Ma, covering most of the igneous history of the Great Basin where my goal of this project is to investigate the Paleogene volcanism within the FCM. Samples collected from the FCM and surrounding Tobin and Shoshone Ranges are Eocene-Oligocene in age (33-34 Ma), calc-alkaline basaltic andesites through to rhyolites. Incompatible elements and isotopic data suggest continental margin subduction-like trace element signatures with highly radiogenic 87Sr/86Sr, consistent with an old, metasomatized lithospheric mantle source. Compared to other areas of the Ancestral Cascades and Western Great Basin, elevated 87Sr/86Sr found in the FCM lavas are herein interpreted to be the result of a purely lithospheric component, suggesting a thicker crust in the central Great Basin. These intermediate, mantle-derived magmas ascended and mixed with partial melts of the mafic crust to form andesites and dacite.