Dynamic model for Pb isotope evolution in the continental crust of China.

A dynamic model of Pb isotope evolution has been established for the continental crust of China in terms of a modification to plumbotectonics with the constraints from the Pb isotopic ratios of feldspars in China Mesozoic Cenozoic granites. Comparing with the evolutionary curves of Pb isotopes for the mean earth,the continental crust in China is characterized by U depletion and Th enrichment and by more compelete differentiation between the upper crust and the lower crust. As a case example,Pb isotopic data for feldspars in the granites of the Dabie Mountains are tested for the dynamic model. The results show that the Pb isotopic data suggest a mixing between the crust and the mantle in different proportions. The Dabie granites could be derived from a mixing between the upper crust and the lower crust,and thus exhibit mantle like Pb isotopic feature on the one hand,and contain higher proportions of the Th rich lower crust component on the other hand.