资源环境科技发展态势分析平台

How the crust thickens to double the normal continental crust is a key issue in the formation of the Tibetan Plateau. Using data recorded by a new 2-D broadband seismic array, we extracted the crustal thicknesses and average V_P/V_S ratios in central Tibet from receiver functions. In our results, the crustal thicknesses increase southward, while the crustal average V_P/V_S ratios generally decrease southward. The lower V_P/V_S ratios in the crust seem to be produced by higher silica contents. We suggest that upper mantle magmas induced by the subduction of Indian lithospheric and Tethyan oceanic slabs underplating the overriding crust differentiate into felsic melts and mafic residues. Mafic residues delaminate into the mantle due to their high density, while felsic magmas are retained in the crust. As a result, crustal thickening in southern Tibet is accompanied by increasing silica contents.