Pb-Sr-Nd-Ar Isotopic Behavior in Deeply Subducted Crustal Rocks

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9316841 Tilton This project will continue parallel isotopic studies of coesite-bearing metamorphic rocks in the Dora Maira massif, Italian West Alps, and the Dabie Mountains, south central China. Recent work in these continental collision zones indicate that continental crustal material has been subducted to depths of at least 100 km, yet has maintained its original crustal character throughout subduction and exhumation. The PI proposes to conduct isotopic studies in these orogenic belts, which are excellent for delineating rates of processes and time and style of petrogenetic settings. The two main purposes of the project are: (1) to develop better understanding of geochronometric systems in ultra high-pressure rocks by resolving differences in the U- Pb and Ar-Ar systems, contrasting Th and U inheritance in monazite, and testing the applicability of the Sm-Nd system; and (2) to provide age and isotopic evidence for geologic and petrogenetic evolution of the collisional and orogenic belts.