Inversion of the density structure of the lithosphere in the North China Craton from GOCE satellite gravity gradient data

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Lithospheric thinning in the North China Craton (NCC), one of the oldest cratons on Earth, has been a focus of geoscientists across the globe for a long time. In this study, seismic tomographic P-wave velocity variations are converted to density perturbations as the initial constraint values, and the four components of the GOCE Level-2 gravity gradient product are subjected to topographic effect correction, relief correction on the Moho and sedimentary layer boundary, and long-wavelength correction. In addition, the anomalous gravity gradient effect resulting from the uncertainty of the Moho and sedimentary layer depth is considered. Considering the effects of temperature variations in the lithosphere, which leads to the non-uniform density distribution, the anomalous gravity gradient effect resulting from the temperature variations is corrected at the first time in this area. Inverse computation is performed based on the preconditioned conjugate gradient algorithm. Because the Lagrange empirical parameter in the algorithm exhibits uncertainty in data inversion, the regularization parameter, which is typically an empirical parameter, is replaced with the value of the inflection point of the L-curve. The results show the followings. The non-uniform density distribution in the lithosphere is related not only to the composition but also to the internal temperature variations in the lithosphere. The density of the lithosphere in the NCC is significantly non-uniform in both the horizontal and vertical directions and exhibits a notable segment-wise spatial distribution pattern. Two tectonic units, namely the Taihangshan tectonic zone and the Linfen–Weihe graben, constitute a central gravity gradient transition zone. There is a significant difference in the density distribution on the two sides of this central transition zone.