Overview of regional gravity field computation models and application of a novel method in imaging the lithospheric architecture and destruction of the North China Craton

Abstract

Abstract The separation of regional and residual gravity fields, arising from deeper and shallower geological structures, has remained a major challenge. In this study, we provide an overview of the various methods, and present the details of a recently developed methodology, based on Finite Element Approach, which does not require a priori assumptions to resolve the regional and residual gravity components. We take the North China Craton (NCC) as a case-study, where previous geological and geophysical studies have demonstrated extensive lithospheric thinning and craton destruction. The residual gravity anomaly map that we computed based on this novel method clearly demarcates the geotectonic boundaries and compare with those from other methods. We identify three prominent gravity high zones located over the Central Asian Orogenic Belt and the Inner Mongolia Suture Zone (Khondalite Belt) in the west, and over the Jizhong depression in the east. The nearly circular anomaly obtained over the Jizhong depression covers an area of ~200,000\xa0km2, which may represent extensive magmatism generated by the hot asthenospheric upwelling. This anomaly cannot be explained by only subduction related melting phenomenon. The 2½D residual gravity modeling across an E-W profile covering the entire North China Craton reveals shallow depth to the Moho and lithosphere-asthenosphere boundary (LAB) at 35\xa0km and 70\xa0km respectively below the Eastern Block, and 50\xa0km and 140\xa0km respectively, below the Western Block. This would suggest almost 100–150\xa0km removal of the lithospheric keel of the NCC. Consequently, a 15\xa0km thick layer of lower crustal and upper-mantle magma, which may be differentiated, is considered to have been emplaced below the Jizhong depression, which is well reflected by the presence of a highly positive residual gravity anomaly (+ 90 mGal) over this region. The average crustal density computed from the present gravity model is found to be relatively higher (2.87\xa0g/cm3) in the Western Block, compared to that in the Eastern Block (2.80\xa0g/cm3) of the NCC. Our study provides further insights into the lithospheric architecture of the North China Craton and the extensive cratonic destruction.