The crustal thickness of NE Tibet and its implication for crustal shortening

Abstract

The crustal deformation model for NE Tibet is key to understanding the outward growth of the plateau, especially along its northern front. This study describes receiver function images of the Moho beneath NE Tibet, as calculated from teleseismic data recorded by regional seismic networks. Moho depth from these images, coupled with results from previous wide-angle reflection/refraction studies (WARR), allowed crustal thickness estimates along several profiles. Crustal shortening was estimated by restoring the present day thickened crust to its assumed initial crustal thickness. Our results show a relatively large amount of crustal shortening (250–350km) at an orientation of N30°E in the central part of NE Tibet. This indicates that prior to shortening, the southern edge of Asia lay 300–400km north of the location indicated by previous S-wave receiver function studies. This discrepancy may result from southward subduction of a segment of Asia's lower-crust beneath central Tibet. It could also arise from crustal thickening predominantly caused by upper-crustal shortening, provided that delamination of eclogitized mafic lower-crust and erosion have not significantly reduced crustal volume.