Petrography, geochemistry and isotopic analysis of paleogene volcanism in the Fish Creek Mountains, Great Basin, North-Central Nevada

Abstract

The Fish Creek Mountains, located in north-central Nevada, is a site of multiple igneous events ranging from 3 5 Ma to IMa, 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 87 Sr/ Sr, consistent with an old, metasomatized lithospheric mantle source. Compared to other areas of the Ancestral Cascades and Western Great Basin, elevated 87 Sr/ 86 Sr 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. II

Geochemical Evolution of Eocene Lakes in the Nevada Hinterland of the North American Cordillera

“…Rivers with higher Sr concentrations have lower 87 Sr/ 86 Sr ratios than rivers with low Sr concentrations, reflecting the high Sr content of carbonate strata (cf., Figures 1 and 5). Eocene volcanic rocks in northeastern Nevada also have relatively low 87 Sr/ 86 Sr ratios (Figures 1 and 5; mean = 0.7069; Gans et al., 1989; Stevens, 2013; Wright & Wooden, 1991). Jurassic and Cretaceous backarc plutons in Nevada and Utah have variable 87 Sr/ 86 Sr ratios (Farmer & DePaolo, 1983; Kistler & Lee, 1989), but the highest 87 Sr/ 86 Sr ratios in these plutons significantly exceed all Paleozoic rocks in the region.…”