Crustal structure and composition beneath the northeastern Tibetan plateau from receiver function analysis

Abstract

We analyzed hundreds of P-wave receiver function data recorded by 53 portable seismic stations to investigate the crustal structure beneath the NE Tibetan plateau. The Moho depths identified by this study reveal that the crustal thickness decreases laterally from the Qilian Orogen (∼63km) to east Kunlun fault (EKLF) area (∼44km). The Moho depth becomes obviously deeper northeast of Songpan–Ganzi terrane and beneath the Qilian Orogen. A remarkable contrast is observed in the measured Poisson’s ratio between the Qilian Orogen and EKLF area. The Qilian Orogen is characterized by lower Poisson’s ratio. In general, the higher Poisson’s ratios (υ>0.30) in the EKLF area can be considered as the evidence for dominantly mafic rocks in the crust. The measured low Poisson’s ratio and the negative correlations between VP/VS and the crustal thickness beneath the Qilian Orogen suggest dominantly felsic crust beneath the Qilian Orogen, which is in contrast with the mid-to-lower low-velocity crustal model beneath the NE margin of the Tibetan plateau indicating that the low velocity zone terminates beneath the east Kunlun area. The seismic evidence suggests that the thickened crust is probably resulted from superposition of the successive intracrustal thrusts. Our results reveal the lateral inhomogeneity of crustal structure in this area and are inconsistent with the scenario of an inflated crust due to extrusion of lower crust material from the central Tibetan plateau.