Gravity data inversion for the lithospheric density structure beneath North China Craton from EGM 2008 model

Abstract

The density structures of the crust and upper mantle beneath the North China Craton (NCC) are reconstructed in this paper by using the Bouguer gravity anomaly derived from EGM08 model. The Occam’s inversion method and preconditioned conjugate gradient (PCG) are adopted in our paper for solving the 3D density inversion problems. Then the depth weighted function is incorporated into model parameters to avoid the skin effects in inversion. In our study, the Bouguer gravity anomaly derived from EGM08 model is used to study the crust and upper mantle structures beneath the NCC. For reducing the non-uniqueness of our inversion problem, we use the inverted density distribution from 0.5° × 0.5° P-wave tomographic results as our initial model. Finally, the high-resolution 3D density model is established down to 250 km depth for the first time in this region. The density images at eight representative layers (10, 25, 40, 60, 80, 120, 160, 200 km) and eight vertical cross-sections (linear profiles along latitude 35°, 36°, 37°, 38°, 39°, 40°, longitude 108°, 119°) are displayed and compared with the P-wave velocity tomographic images. The 3D-dimensional density model indicates that lateral heterogeneities are widely distributed in different units within the NCC, while their density patterns and depth extensions are significantly different for three main units of NCC, suggesting different tectonic mechanisms that have dominated the evolution of these regions in the Phanerozoic. In particular, our inverted density images demonstrate that the Phanerozoic lithospheric reactivation and thinning may not have influenced the central and western NCC to the same extent as the eastern NCC, most of which preserves relatively thick cratonic lithosphere today. However, localized lithospheric thinning may exist in the circular-Ordos rift systems, whose ancient tectonic belts around the Ordos plateau may have been affected by multi-phase tectonic events in its long evolution history.