In-situ central Qiangtang metamorphic belt in western Tibet as a typical suture zone: Evidence of crust-mantle structural footprints from P-wave receiver function analyses

Abstract

Whether the central metamorphic belt of the Qiangtang terrane in the Qinghai-Tibet Plateau should be attributed to a suture zone, is still heavily debated, due to inadequate deep structure constraints. Using the data collected from 16 stations in the northern part of the Hi-Climb profile and 16 broadband seismic stations recently arranged in the northern part of Gaize County, this study developed a broadband seismic profile running through the in-situ Central Qiangtang Metamorphic Belt (CQMB) roughly along 84.5°E. Significantly characteristics of the crust and mantle structure beneath the profile were obtained through P-wave receiver function analyses: (i) The south Qiangtang terrane has a complex Moho structure at depth 56–82 km, while the north Qiangtang terrane has a nearly horizontal Moho at depth approximately 62 km. Moreover, the northward-inclining Moho is noticeably dislocated with a maximum offset of approximately 18 km under the CQMB. (ii) The crustal low-velocity zones on both sides of the CQMB are transversely discontinuous and are also distinct from each other. (iii) A northward-subducting interface occurs beneath the in-situ CQMB (34.0°N–34.5° N). Based on the geological outcrops and their petrological analysis, the structural characteristics beneath the CQMB are interpreted as the traces of the Longmucuo-Shuanghu suture zone, which was formed by the northward subduction-collision of the south Qiangtang terrane left after the closure of the Paleo-Tethys Ocean at the end of the Triassic.