Collaborative Research: Cenozoic Tectonic and Magmatic Evolution of the Mojave Desert: Constraints from Isotopic and Trace-Element Compositions of Volcanic Rocks

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This is a collaborative study between the University of Colorado and the University of North Carolina on the Nd, Sr, and Pb isotopic, and trace element compositions of Cenozoic mafic-to- silicic volcanic rocks in the Mojave Desert region of southeastern California. The study will use temporal and spatial variations in the geochemical characteristics of the volcanic rocks to constrain models of the tectonic evolution of this region, and to study aspects of the magmatic evolution of the Cenozoic volcanic rocks. Geochemical data from 5Ma basalts will be used to evaluate the age, structure, and composition of the mantle currently underlying this area. The results of this study will be used to test whether pre-Cenozoic mantle lithosphere has been tectonically removed from beneath the continental crust, as suggested by available isotopic data and as proposed in some tectonic models for this region. Geochemical data from older Cenozoic basalts will be used to assess the tectonic setting in which lithosphere removal took place. A similar geochemical data set will be obtained for Miocene intermediate-to-silicic volcanics and will be used to constrain models for the genesis of these rocks. The isotopic compositions of these rocks will also be used to infer aspects of the geochemistry of the lower continental crust, and to define any subsurface boundaries between Precambrian basement terraines with different Nd isotopic characteristics. Overall this study will represent the first comprehensive characterization of the isotope and trace element compositions of Mojave volcanic rocks, and one of the first attempts to apply such data towards constraining tectonic models of the continental lithosphere. The study represents an outgrowth from previous NSF supported research by both of the PIs. Glazner (UNC) will be responsible for sample selection, petrography and trace-element chemistry, and Farmer (UC) will carry out all isotopic determinations.