A Window Into Deep Lithospheric Processes of the Western U.S. From Os Isotope Investigations of Mantle Xenoliths

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RudnickEAR-9909526We propose to investigate the tectonic processes occurring in the deep lithosphere of the SW US through studies of mantle xenoliths erupted along an E-W transect from the Sierra Nevada to the Colorado Plateau. Petrography, mineral and major element chemistry, thermobarometry and Re-Os isotopic compositions will be determined for several suites of mantle xenoliths from the Sierra Nevada mountains (Big Creek and Oak Creek), the Basin and Range (Cima volcanic field) and the Colorado Plateau (the Thumb). This traverse samples Proterozoic crust that has been subjected to diverse tectonic influences: arc magmatism (Sierra Nevada), compressional tectonism (Colorado Plateau) and back-arc extension (basin and range). The goal is to map the lithospheric mantle in these diverse regions in order to determine the present day thickness and age of the lithosphere. These data will then be integrated with surface geology and geophysical remote sensing of lithospheric structure to infer the processes that have shaped the deep lithosphere.