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Abstract

The continental collision between the Indian and Eurasian plates in the Cenozoic not only produced the Tibetan Plateau (TP) but also pushed a large volume of continental lithosphere out of the plateau southeastwards. It has been strongly debated for many years how to transport mass from the central plateau to the southeastern TP. In the neck area between the central plateau and its southeastern margin, we deployed a SW‒NE-trending dense seismic nodal array to record teleseismic waveforms. Receiver function methods were used to estimate the crustal bulk properties and to image the crustal structure. Our results show that the crustal thickness is approximately 60 km and the crustal average Vp/Vs ratios are approximately 1.78, which are less than the predicted values of the crustal channel flow model. In the crustal structure image, the Moho beneath the southwestern part of the profile dips northeast and extends below the Moho beneath the northeastern part of the profile. Beneath the southwestern part of the profile, a lower crustal northeast-dipping interface is also imaged, which is likely linked with the Jinsha River suture. Our results suggest that the most significant crustal thickening in the southeastern TP was produced by the northwards or northeastwards subduction of the Qiangtang block, which occurred in the late Oligocene to early Miocene, as indicated by palaeo-altimetric studies. Our results imply that the modern landform in the southeastern TP resulted from southeastwards block extrusion along strike-slip faults and more monsoonal precipitation and seasonal climate variation since the late Miocene.