Isostatic state and crustal structure of North China Craton derived from GOCE gravity data

Abstract

The crustal structure between different subregions of the North China craton (NCC) plays an important role in improving our understanding on the craton evolution. Here we present a flexural Moho map and isostatic residual gravity field of the NCC derived from the GO_CONS_GCF_2_TIM_R3 model.We first investigate the influence of additional sources on the forward flexure calculation, especially the distinct thinning of the lithospheric thickness from west to east. After removing the gravity effects of the LAB undulations, the flexural Moho and isostatic residual gravity field of the NCC are calculated using the Vening-Meinesz regional isostasy models. There are high to medium positive residual anomalies beneath the Eastern block and Trans-North China Orogen, while negative residual anomalies delineate the Yinshan block, Ordos plateau and Khondalite belt. This obvious disparity is consistent well with the decreasing depth of the flexural Moho from west to the east. A profile across the Eastern block, Trans-North China orogen and the Western block was employed to construct a density structure of the crust and uppermost mantle. By comparing the surface topography, Bouguer gravity, isostatic Moho and seismological Moho undulations, we find that the flexural Moho is much shallower than the seismic Moho beneath the northern margin of the Ordos block, possibly indicating the over-compensated isostatic state caused by the dominant NW–SE oriented compressional deformation in the lithospheric processes. Density modeling results further predicted that a high density body may exist in the lower crust beneath the northern margin of the Ordos block, which could be a westward-dipping upper-middle crust remnant stagnating in the lower crust beneath the Western block. Medium to high pressure metamorphism of granulite facies or eclogite facies, resulting from subsequent continental thickening during the continental collision may be responsible for modifying the remaining subduction remnant.