Research over the last several years has shown that a lower Paleozoic magmatic, metamorphic and deformational event affected the Greater Himalayan Sequence (GHS) in Nepal and India. The purpose of the proposed research is to determine whether this event was sufficiently intense and widespread to significantly metamorphose the main belts of Greater and Lesser Himalayan rocks and affect the retrieval of Cenozoic P-T conditions. Garnets will first be mapped for trace elements via LA-ICP-MS, cores vs rims of garnets will be mechanically separated and, together with matrix and matrix mineral separates, will be dated via MC-ICP-MS. Recently developed Lu-Hf dating methods allow chronology of these garnet separates with high precision (<1%). Sm-Nd isotope data will also be collected as a check on Lu-Hf ages. This work has major broad implications for the evolution of the Himalayan orogen, including the relevance of previously reported P-T conditions as constraints on Miocene tectonics. This work also has broader implications for the reliability of chemical zoning in garnet as a robust recorder of polymetamorphic events. This research will provide training for the PI in new techniques in radiogenic isotope geochemistry that in turn can be disseminated to the metamorphic petrology community as well as to students at USC.
