Diachronous lithospheric thinning of the North China Craton and formation of the Daxin'anling–Taihangshan gravity lineament

Abstract

The Daxin'anling–Taihangshan or North–South Gravity Lineament (NSGL) is an important geologic zone within the North China Craton (NCC). Crustal elevation, morphology, crustal and lithospheric thickness and gravity anomalies all change considerably across the NSGL. However, the timing of formation and the mechanism are poorly understood. Comparison of on-craton Cenozoic basalts and their included xenoliths reveals that the NSGL is not only a physical boundary but also a chemical “discontinuity” that separates two different mantle domains. Mantle xenoliths from the western NCC have a wider range in isotopes than those from eastern China. In particular, they show the lowest ε Nd and 187Os/ 188Os ratios. Such a lateral heterogeneity may have resulted from lithospheric extension within the NCC, that was diachronously taking place in the east in the Mesozoic and that in the west in the Cenozoic. Such processes could have produced differences in lithospheric thickness underneath the western and eastern NCC during the Cretaceous, eventually giving birth to the NSGL. Formation of the NSGL by diachronous lithospheric thinning is supported by paleogeographic data, which indicates the presence of the NSGL in the early Cretaceous, a period of peak magmatism within the NCC. It is proposed that the NSGL might represent the interaction front between two tectonic regimes, with back-arc extension related to Pacific subduction in the east and Indo-Eurasian collisional extension in the west. The location of the NSGL could be controlled by the western boundary of the vigorous convection induced by stagnant oceanic slabs in the mantle transition zone and old major lithospheric weak zones in the region.