Acomplishment Based Renewal (ABR): Trace Element Distribution Within, Between, and Among Metamorphic Minerals

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

Spear EAR-0337413 The distribution of certain trace elements among minerals in metamorphic rocks has been shown by the P.I. and co-workers under prior NSF grants to be a sensitive monitor of metamorphic P-T conditions and reaction history. The strongest trace element signature was found in rocks of low to medium metamorphic grade where estimates of temperature changes during crystallization of garnet of only a few degrees could be discerned. At higher metamorphic grades, trace element concentrations become significantly lower in garnet, requiring more sensitive analytical instruments to make the concentration measurements. This proposal seeks to extend this work to more extreme crustal conditions by examining high-grade rocks from the Adirondack Mountains, New York, the Cordillera Darwin, southern Chile, and the Valhalla Complex, eastern British Columbia using trace-element sensitive analytical techniques (LA-ICP-MS and SIMS). A major goal will be to extend the empirical thermometers developed under the prior grant to these higher conditions. A second goal will be to decipher the paragenesis and stability range of the accessory mineral monazite, so that meaningful interpretations of U-Th-Pb ages of this mineral can be made. The results of this study will be widely applicable to research by petrologists and geochemists that use geochronology on accessory minerals in orogenic terranes worldwide. Ultimately, these results should provide significantly deeper and more detailed insights into the processes that operate during orogenesis. The PI will support a female graduate student in this project.