The role of lithospheric heterogeneities in continental rifting: Implications for rift diversity in the North China Craton

Abstract

Widespread heterogeneities exist in the continental lithosphere, but their role in continental rifting is poorly understood. Here we investigate the influence of lithospheric heterogeneities on the pattern of continental rifting using 2D thermo-mechanical simulations. The heterogeneities are mainly manifest in a laterally inhomogeneous continental lithosphere, which has a cold west (CW) half and a hot east (HE) half. A series of experiments were performed to examine the effects of lithospheric thermal state, weak zones, and extension velocity on continental rifting. The results show that: (1) stretching of a CWHE lithosphere always leads to the formation of a wide rift at the HE side, while the CW side remains largely undeformed; (2) the presence of a weak zone in the CW lithosphere can cause a wide rift to form at the eastern side and a deep narrow rift to form synchronously at the western side; and (3) the lithospheric thermal state strongly affects the style of rifting and the lithospheric deformation mode. When the crust is extremely hot (TMoho = 900 ℃), a wide rift first develops at the HE side, which is followed by the formation of a narrow rift at the CW side. The extension velocity mainly affects the timing of rift formation but has no significant effect on the style of rifting. A number of rift basins have developed in the North China Craton (NCC) since the early Cenozoic in response to the retreat of the Pacific plate subduction. The eastern NCC is dominated by wide rifts, whereas the western NCC is dominated by narrow rifts. We suggest that the coexistence of these two types of rift in the NCC is the result of lateral lithospheric heterogeneities, which include pre-existing lithospheric weaknesses. The differences in the thermal and rheological states between the Eastern Block and Western Block of the NCC prior to extension were likely to cause the wide rifts at the east and the narrow rifts at the west.