Lithosphere Density Modeling Based On Multi-source Gravity: Methods And Applications

Lithosphere density structure is essential for studying geodynamics, geotectonic divisions, tectonic evolution and large-scale gravity; gravity inversion is one of the effective ways for constructing lithosphere density. Therefore this paper studied and applied related methodologies aiming at constructing lithosphere density structure by gravity study.We calculated the marine gravity anomaly field of the South China Sea by taking the vertical deflection method based on the altimetry data from several satellites. The ship gravity datasets which belong to different voyages were collected and processed; the systematic errors were removed through surveying grid adjustment. One kind of multi-source gravity field fusion method based on wavelet analysis was proposed; we designed different fusion strategies for different frequency coefficients and also discussed the differences of the fusion results when based on different wavelet functions. This fusion method was applied in the South China Sea region and application results showed its effectiveness. The multi-source gravity field fusion method based on wavelet analysis is the new way to fuse multi-source gravity field quickly and accurately.One kind of corner-point grid model was designed for providing infrastructural model for density structure and interactive gravity inversion. The methodologies and work flows for interactive gravity inversion: create some 2D profiles according to the 3D geomodel and edit the profiles interactively; forward gravity field in the frequency field in parallel based on the 3D geomodel; revise the initial 3D geomodel according to the edit results of the profiles. It improves the reliability of the forward field when based on 3D model, and it improves the flexibility for interacting with 3D geomodel when by 2D profiles.We studied the relationship between buried depth, porosity and density of the sediment, the methods for calculating temperature field of the lithospheric mantle and the relationship between density and the temperature and pressure of the lithospheric mantle. Basement thickness inversion flow was designed, and the parameter values for sediment density and lithospheric mantle density modeling, basement density and the Moho depth can be derived through this flow.We collected seafloor depth, topography, sediment thickness and interpretation results of some deep seismic lines in the South China Sea region. According to the density modeling methods and the gravity inversion flow, by taking seismic data as restrain, we obtained the best parameter values for density modeling and the density and thickness of basement of the South China Sea. The 3D lithosphere density model of the South China Sea was constructed by the software of this paper based on the interface depth and density structure of each layer; and then the initial 3D model was revised according to the seismic profiles.Restored the original shapes of the conjugate margins of the present South China Sea according to the lithospheric density model and the evolution history of the South China Sea; the rotation pole for moving the southern margin to its original location at late Cretaceous was derived and this rotation pole was used for creating the full-fit plate reconstruction model. At last, this paper analyzed the evolution history of each block, sea basin and the sediment basins in this region by taking this reconstruction model as the initial state.