9725287 Feeley This is a proposal designed to carry out a geological and geochemical transect across the northern part of the Absaroka volcanic field, Wyoming. Because the Absaroka volcanic rocks record one of the most voluminous and compositionally diverse magmatic episodes to affect the Cordillera during the Eocene, the results obtained from this study will significantly improve our knowledge of the ages, compositions, and petrogenesis of Tertiary magmatism in the northern Rocky Mountains. This, in turn, will provide insight into the fundamental problem of how rock suites with potentially arc-like calc-alkaline affinities and across-strike geochemical trends can form in such different tectonic environments, and possibly in the absence of contemporaneous subduction. The analytical work will include analysis of major and trace elements by XRF and ICP-MS, analysis of Sr, Nd, and Pb isotopic ratios by TIMS, and mineral analysis by electron microprobe. Overall, this study represents a realistic first approach towards providing a modern petrologic perspective on one of the outstanding unresolved issues in deciphering the Cenozoic geological history of the northwestern United States: namely, the origin of the Absaroka magmatic rocks.
