Concordant structural variations from the surface to the base of the upper mantle in the North China Craton and its tectonic implications

This study presents an integrated study of the North China Craton (NCC) based on recent high-resolution seismic images combined with observations on surface geology, regional tectonics and mantle dynamics. Seismic images reveal markedly concordant and rapid variations in crustal and lithospheric structure and thickness, upper mantle anisotropy, and discontinuity structures and thickness of the mantle transition zone near the boundary between the eastern and central parts of the NCC. These rapid variations roughly coincide with the sudden change in both surface topography and gravity field as marked by the North–South Gravity Lineament (NSGL). Such a shallow–deep structural concordance may reflect different lithospheric tectonics and mantle processes in the two domains during the Phanerozoic reactivation of the craton. Sharp structural variations are particularly present to the west of the NSGL, especially between the Archean Ordos Plateau, which retains the characteristics of a typical craton, and the surrounding Cenozoic rift systems which are underlain by a significantly modified and thinned lithosphere. These observations provide deep structural evidence that the Phanerozoic reactivation was not confined to the eastern NCC as previously thought, but also affected areas in the central and western NCC, though to a much lesser degree. On both sides of the NSGL, lithospheric modification and thinning appear to be more pronounced along Paleoproterozoic belts suturing Archean blocks, demonstrating the importance of pre-existing lithosphere-scale structures in controlling the tectonic evolution of the NCC. It further indicates that craton reactivation probably is common given the fact that structural heterogeneities are always present in cratonic regions. The seismic structural images together with geological, petrological, geochemical and mineral physics data suggest that the fundamental destruction of the eastern NCC lithosphere may have been triggered largely by the deep subduction of the Pacific plate, especially during the Late Mesozoic. The complexity of deep structures and lithospheric properties in regions west of the NSGL may represent the relatively weak imprints of the Cenozoic India–Eurasia collision superposed upon that of the earlier tectonic events.