Multiscale geophysical characterization of the continental crust of the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is a Paleozoic accretionary-collisional orogen located at the eastern Pangea in between the Siberian Craton to the north and the North China and Tarim cratons to the south. Several contradictory geodynamic models were proposed to explain the tectonic assemblage: oroclinal bending and strike-slip duplication of a giant intraoceanic arc or a progressive lateral accretion of linear continental and oceanic terranes towards the Siberian Craton. However, none is generally accepted. A multidisciplinary and multiscale approach integrating potential field analysis and modelling provides new insights into understanding the crustal structures beneath the CAOB.

First, we present a synthesis of the previous geophysical studies, which constitute the constraints for the modelling. Second, based on global gravity and magnetic anomaly grids, the large-scale statistical analysis of their lineaments reveals the distribution of the contrasting tectonic zones. Then, the topography of the Moho is determined by 3D forward modelling of the GOCE gravity gradients, which is then integrated into 2D and 3D crustal scale models of southern and central Mongolia. A geodynamic model is derived from the resulting crustal architectures. Thus, the combination of these methods allows us to: (1) unravel the existence and distribution of suspect terranes in accretionary systems; (2) correlate the contrasting tectonic zones with the gravity and magnetic signals and the thickness of the crust, thereby revealing the inheritance of Paleozoic and Mesozoic orogenic history; and (3) determine the significance and possible origin of the major anomalies, which are related to tectonic processes such as lower crustal relamination, presence of deep-seated fault zones and sutures, or delimitation of main tectonomagmatic domains. Finally, with the case study of Central Mongolia, we demonstrate the real benefit and the significant progress, which can be achieved by using potential field analysis combined with seismic receiver function and geological analyses.