Detection of southward intracontinental subduction of Tibetan lithosphere along the Bangong-Nujiang suture by P-to-S converted waves

Abstract

Teleseismic primary (P) to secondary (S) converted waves recorded on the INDEPTH III seismic array have been used to detect lithospheric-scale deformation structures of the central Tibetan Plateau from the central Lhasa terrane to the central Qiangtang terrane. A south-dipping crustal converter is seen from the upper crust near the 500-km-long metamorphic core complex exposures in the Qiangtang terrane to the lower crust near the Bangong-Nujiang suture. At deeper depths, a southeast-dipping mantle converter is seen extending from ∼50 km north of the Bangong- Nujiang suture at the depth of the Moho, to a depth of ∼180 km, ∼100 km south of the Bangong-Nujiang suture. We found the observations to be most consistent with a model of lithospheric deformation involving (1) southward subduction of the Tibetan lithospheric mantle along the Bangong-Nujiang suture and (2) thickening of the central Tibetan crust through a thick-skinned, crustal accretionary thrust-wedge structure in response to the India9s collision with Asia.