Lithospheric Shear Wave Tomography Of Continental China By Joint Inversion Of Surface-wave And Satellite Gravity Data

Continental China and its surrounding regions are located in a unique tectonic setting where the Paleo-Asian Ocean Domain,the Tethyan Domain,and Western Pacific Domain met in a triangular framework,forming one of the most geologically complex and tectonically active regions on Earth.The Mesozoic-Cenozoic destruction of the north China craton(NCC)and the Cenozoic rise of the Tibetan Plateau(TP)are the two most significant tectonic events in relatively recent geological times.Detailed knowledge about the structural heterogeneities of the lithosphere beneath the continental China is the key for better understanding of these intensive geodynamic processes.A simultaneous inversion of multiple,consistent,and complementary datasets is an effective way to reduce the non-uniqueness and improve the reliability of geophysical inversion.In this study,we obtain a self-consistent three-dimensional shear-wave velocity and density model beneath the continental China from joint inversion of surface-wave dispersion and gravity observations.It is well known that surface wave dispersion measurements are sensitive to seismic shear wave velocities,and the gravity measurements supply constraints on rock density variations.To combine surface wave dispersion and gravity observations into a single inversion framework,we use an empirical relationship between seismic velocity and density constructed through the combination of two empirical relations.One is determined by Nafe and Drake that is mostly appropriate for sedimentary rocks,and the other is the linear Birch's law that is more applicable to denser rocks.We have applied the method to investigate the structure of the crust and upper mantle beneath the continental region.The Vs model obtained from joint inversion fits the surface-wave dispersion data at least as well as separate surface wave inversion while the gravity anomalies are much better fitted when included in the inversion.We also explained the results in some regions,such as crustal footprint of the Hainan plume beneath southeast China.Our results show that a linear corridor of high seismic velocity anomalies at the base of the crust is located northeast of Hainan Island beneath southeast China.Geodynamic modeling further demonstrates that this corridor could have been formed by the interactions between a mantle plume and the continental lithosphere with a weak lower crust.Our result provides a novel explanation for the crustal thickness variations,related Vs anomalies and observed OIBs in this area.In summary,our new joint inversion model shows more detailed structures than separate inversions and could provide a better reference model for other studies in China.