When did the large-scale extensional tectonics begin in North China Craton?

Abstract

In response to the craton destruction, the North China Craton (NCC) underwent the Early Cretaceous extensional tectonics. During this period, the eastern NCC has also experienced numerous plutonism, volcanism, and extensional structures. Particularly, half-graben or graben, Early Cretaceous extensional domes, metamorphic core complex, and syn-kinematic plutons are widespread throughout the NCC and its surrounding area, with a peaking age of 125 Ma, pointing to a large-scale severe NW-SE extension. However, it remains unknown when and how the large-scale extension is initiated. To answer this key issue, we choose two plutons (Fengjiayu-Xibailianyu and Gubeikou plutons) with the age of early stage of the Early Cretaceous (130–127 Ma) as the target of this study. The Fengjiayu-Xibailianyu pluton is close to, while the Gubeikou pluton is far away from the Early Cretaceous intensive extensional region. A multidisciplinary study, including structural geology, anisotropy of magnetic susceptibility (AMS), and gravity modeling, has been carried out on these two plutons to reveal the tectonic regime coeval with their emplacement. Both of these two plutons share similar features of concentric magnetic foliations and variable magnetic lineations which are decoupled with the ductile fabric in their country rocks. Accordingly, we considered that they intruded in a permissive way at a weak extension regime during the Early Cretaceous (130–127 Ma), just before the Late Mesozoic peak of the magma flare-up and large-scale extensional tectonics of the NCC. Combined with our previous works, the Early Cretaceous NW-SE trending extension in NCC was further subdivided into the early-stage weak extension during 130–127 Ma and the late-stage intensive extension during 127–110 Ma, namely the large-scale extension initiated after 127 Ma. The early-stage extension could be ascribed to the westward subduction of the Izanagi plate under the Eurasian continent.