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

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The high pressure polymorph of quartz, coesite, has been reported from metamorphic rocks in three mountain belts, and indicates subduction to depths in excess of 100km followed by return to the earth's surface. This project will focus on the occurrence of coesite in the Dabie Mountains of east central China, within a presumed suture zone between the Yangtze and Sino-Korean cratons. Major aims are to date the parent rock, the age of high pressure metamorphism and the time of collision of the cratons. The work also includes additional study of coesite-bearing eclogitic rocks within the Dora Maira massif in Italy and comparisons to the China occurrence. Results will provide the basis for a better understanding of the relationship between subduction processes and the timing of ultra-high pressure meta- morphism.