GEOCHEMICAL SUBDIVISION AND EVOLUTION OF THE LITHOSPHERE IN EAST QINLING AND ADJACENT REGIONS - IMPLICATIONS FOR TECTONICS

The crust and upper mantle in East Qinling and the adjacent North Chin a and Yangtze blocks exhibit systematic heterogeneity in Pb and Nd iso topic compositions, whereby two tectono-isotopic provinces of North Ch ina and Yangtze can be identified. The South Qinling on be assigned to the Yangtze province according to its crustal Pb isotopic composition , crustal growth history and upper mantle evolution. The North Qinling is reasonably considered to be an ancient, independent microcontinent and was formed principally in the Proterozoic over the strongly deple ted upper mantle. Some implications of these results for tectonics are discussed.