Significant structural variations beneath the central and western North China Craton: evidence for heterogeneous lithospheric modifications

The North China Craton (NCC) is a classical example of ancient destroyed cratons in the world. Available data suggest that the destruction mainly occurred in the eastern NCC, whereas the central and western NCC was only locally modified, akin to many other stable cratons. While many progresses have been made to understand the cratonic destruction in the east, much less focused on the lithospheric reactivation and modification in the west due largely to the paucity of knowledge on the deep structure. Recently a rapid increase of broadband seismic array observations in the NCC provides a large amount of data, which help to gain a deep insight into this issue. In this study, we present an integrated study of the crustal and lithospheric structure in the central and western NCC based on new high-resolution seismic images combined with observations on surface geology and regional tectonics. Seismic images reveal significant structural variations in the region. The Ordos plateau (the major part of the western NCC) retains the characteristics of a typical craton, preserving the crustal fabrics developed during the early evolution of the NCC and a fast and thick lithosphere with little deformation. The surrounding Yinchuan-Hetao rift, northern Fen-Wei rift and adjacent areas in the northern part of the central NCC and the Qilian orogenic belt are underlain by a heterogeneous crust and slow and thin lithosphere which are in fairly sharp contact with the cratonic lithosphere beneath the Ordos region. In contrast, the middle to southern part of the central NCC including the southern Fen-Wei rift is featured by a relatively thick lithosphere with complicated uppermost mantle structure, similar to that of the Ordos plateau. However, the crust structure of this region exhibits a variation pattern that differs from the Ordos but resembles the northern part of the central NCC. These structural features together with geological, petrological and geochemical data suggest that lithospheric reactivation and modification in the central and western NCC are highly heterogeneous, both laterally and vertically. Lithospheric modification and thinning in these regions appear to have mainly taken place along ancient tectonic weak zones, but in various degrees because of the intrinsic complexity of the lithosphere and different effects of later thermo-tectonic events. The cratonic nucleus in the western NCC may have been efficiently protected by surrounding weak zones and retained its stability over long periods of geological time. The combing effects of pre-existing lithosphere-scale structures and later thermo-tectonic events on the evolution of the central and western NCC may also explain the lithospheric modifications observed in many other cratonic regions where structural heterogeneities are always present.