DISCUSSIONS ON THE LITHOSPHERIC THINNING IN EASTERN CHINA

The lithospheric thinning in eastern China is a warmly discussed topic in the last decade. It is not clear, however, about its time, mechanism and tectonic controlling factor for this kind of geodynamic phenomena. According to the up-dated data, a comprehensive review for these questions is given in this paper. It is suggested that the lithospheric thinning took place in the Late Mesozoic, and maximally thinned in Early Cretaceous (120～130 Ma). It is thought that the lithospheric thinning was related to the subduction of Pacific plate in the east, which resulted in the lithospheric thickening and subsequent delamination. The Os isotopic data from the mantle xenoliths in the Cenozoic basalts suggested that the lithospheric mantle in the Cenozoic is juvenile, much different from that in the Paleozoic, which indicated that the present lithospheric mantle is not the residue after the thinning. Therefore, it is proposed that whole lithospheric mantle with part of the lower crust was delaminated, which resulted in the direct contact between the asthenospheric mantle and crust. The heating from the asthenosphere on the crust subsequently resulted in the intensive magmatism, mineralization, and widespread development of extensional structures in eastern China.