Gravitational gradients derived from GOCE and density structures beneath the North China Craton

Abstract

In this study, the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) gravitational gradients in the North China Craton (NCC) are processed. The normal gravitational gradient correction, the downward continuation from the mean orbit altitude to the geoid, and the gravitational gradient corrections for the topography, sediment, Moho undulations and the deep-source field are taken into account. After processing, the residual gravitational gradient anomalies corresponding to density heterogeneities are acquired. The preconditioned conjugate gradient method is introduced to invert the density structures using the roughness matrix to constrain the density distribution and the depth-weighting function to prevent the density distribution from migrating to the top of the model due to the decay of the gravitational gradient kernel with depth. The density structure derived from the seismic tomography is used as the initial model, and the GOCE gravitational gradient anomalies are used to invert the density structures in the NCC using the preconditioned conjugate gradient method. The results show that the density structures of the NCC lithosphere reflect obvious lateral and vertical heterogeneities. The density structure in the eastern part of the NCC is different from that in the western part of the NCC. The distribution of the density anomalies corresponds to the tectonic characteristics. The density structures in Taihang Mountain exhibit segmentation features. The thinning of the lithosphere observed in the NCC may extend into the northern part of Taihang Mountain. The density changes significantly within the area between the Ordos Block and the Qilian Block, which corresponds with the different lithospheric features in these two blocks.