Why the North China Craton became active 1~2 million years ago after 2 billion years of quiescence? The newest research suggested that its small size and the intra-plate weak zones make it vulnerable to destruction (internal reason). The subductions of the surrounding plates, also contribute to its destabilization (external factor). The subduction and retreating of the (Paleo-) Pacific plate, 1~2 million years ago, was of critical significance because it triggered the thinning and replacement of the lithospheric mantle coupled with basin-mountain respond in the shallow crust. This should be the innate nature of the cratonic destruction and the Yanshan Movement.
The related research paper titled "Subduction and retreating of the western Pacific plate resulted in lithospheric mantle replacement and coupled basin-mountain respond in the North China Craton" was published in Science China Earth Sciences (doi: org/10.1007/s11430-017-9166-8) by Professor Jianping Zheng (corresponding author) from China University of Geosciences (Wuhan). The researchers found that the subduction and retreating of the (Paleo-) Pacific plate could be responsible for the replacement of the lithospheric mantle and the shallow coupled basin-mountain responds in eastern North China Craton. This decratonization, or the Yanshan Movement, should be the collective result of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust.
Craton is ancient continent with cold, buoyant, rigid and thick lithosphere and thus can keep stable for billions of years. However, the Mesozoic North China Craton witnessed vigorous crustal deformation, ubiquitous magmatism, widespread metallogenesis, large-scale basin formation and the transition in the nature of lithospheric mantle. All these indicate the decratonization of the craton. The mechanism, temporal and spatial range and geodynamics accounting for these geological records have been extensively studied. However, the synergistic effect of these processes, including the dynamics relationship between the inner part and margin of the block, and the deep mantle processes with shallow continental crust within the craton, is rarely discussed.
The research showed that external factors include the subduction of the surrounding plates and the resultant upwelling of asthenosphere along the intra-plate weak zones. Before the Middle Jurassic (170 Million years ago), the northern and southern margins of this craton suffered from the syn-collisional compression and then post-collisional extension as recorded by the latitudinal basins, faults and magmatism. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenospheric upwelling and had the priority for magmatism and deformation. Since the Early Cretaceous (140 million years), the decratonization of the North China Craton was characterized by: (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; and (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating.
This paper revealed the links between the complex geological processes proceeding in the deep lithospheric mantle and the shallow continental crust. It is not only of great importance for the research on the North China Craton and the Yanshan Movement but also of significant implications for study on the decratonization, shallow responds of the deep geological processes and the mineralization effects.
This work was supported by the National Key R&D Program of China (Grant No. 2016YFC0600403) and the National Natural Science Foundation of China (Grant No. 91214204).
More detail can be found in the original paper as following: Zheng J P, Dai H K. 2018. Subduction and retreating of the western Pacific plate resulted in lithospheric mantle replacement and coupled basin-mountain respond in the North China Craton. Science China Earth Sciences, 61(4): 406-424