Crust And Upper Mantle Structure Beneath Southeastern China From Joint Analysis Of Receiver Functions And Rayleigh Wave Dispersion

Eastern China is located at the junction of multiple major tectonic regimes,such as the Central Asia orogenic belt to the north,the Pacific and the Philippine plates to the east,and the Tibetan Plateau to the west.The tectonic environment and geological background are very complex in this area.During the Mesozoic,the SE China experienced extensive compression and extension,leading to multiple periods of magmatic activities and the formation of several big ore-concentrated districts.To further understand the Mesozoic magmatic and tectonic activities in SE China,we obtain the crustal thicknesses and the Vp/Vs ratios of the region by H-(?) stacking of receiver functions,and construct a new 3-D shear-wave velocity models of the crust and upper mantle by joint inversion of receiver functions and Rayleigh wave dispersion curves.The crustal thicknesses in the study area vary from ?30 km to ?35 km,and the distribution of the Vp/Vs ratios is complicated.The southeastern coast magmatic belt(SCMB)shows high Vp/Vs ratio(>1.79),indicating that the average composition of the crust in this region contains more mafic components than the west Cathaysia block(WCB).Combined with the relatively high-velocity anomaly in the lower crust of the SCMB,it indicates that there was underplating of mafic material beneath the SCMB.At asthenospheric depths,the shear-wave velocity of the SCMB is lower than that of the WCB,suggesting more intensive asthenospheric partial melting beneath the SCMB during the rollback of the Pacific Plate in the Mesozoic.The magmatism of the WCB mainly occurred in the Jurassic(153-164 Ma),whilst that of the SCMB was mainly in the Cretaceous(87-146 Ma)and was feature by more mafic components.Therefore,the asthenospheric melting is more recent and intense beneath the SCMB than that of the WCB,generally consistent with our model.Previous studies showed that the crustal basements of the WCB and the SCMB are quite different,likely resulting in contrasting rheological strength.In addition,the water content of the subducting Paleo-Pacific slab is likely higher beneath the SCMB than beneath the WCB due to its proximity to the plate boundary,causing more intensive asthenospheric partial melting beneath the SCMB due to the rollback of the Paleo-Pacific Plate.We speculate that the more intensive Mesozoic magmatism and crustal extension in the SCMB likely results from the two mechanisms mentioned above.