Ultra-high pressure (UHP) metamorphism (at depths >80 km) is a product of continental subduction and collision. Investigation of UHP metamorphic rocks and the processes responsible for their exhumation and exposure at the Earth's surface aids our understanding of continental evolution and crust/mantle geochemical processes. This study will employ zircon U-Pb geochronology, linked to pressure, temperature, and mineral paragenesis by REE geochemistry, mineral inclusion analysis, and thermobarometry, to study the ages of metamorphism in the North Qaidam and South Altun UHP terranes in northwest China, as well as the exhumation rates associated with their eclogite- to granulite- and amphibolite-facies decompression. The results will significantly advance our knowledge of the geologic history of the N. Qaidam and S. Altun terranes, and will evaluate the geochronological correlation proposed between them. In addition, this study will also aid our general understanding of UHP processes, especially those responsible for the preservation of UHP rocks during exhumation and subsequent exposure at the Earth's surface.
The proposed research addresses significant questions both in the field of metamorphic petrology, as well as central Asian tectonics. The PI, graduate student Chris Mattinson, together with collaborators J.L. Wooden, J.S. Yang, and Mattinson's thesis co-advisor J.G. Liou have both the field and laboratory experience necessary to address the questions posed, and the required resources are available at Stanford University. This research is an integral part of graduate student Chris Mattinson's doctoral research, and will result in multiple publications in peer-reviewed journals and presentations at national and international meetings. Central to this research is collaboration with Chinese colleagues, thereby enhancing international scientific exchange and cooperation. The REE analysis routine developed during the preliminary study supports and enhances the state-of-the-art, multi-user Stanford-USGS SHRIMP-RG facility, thereby enhancing the infrastructure for research and education.
