Early Cretaceous extensional reworking of the Triassic HP–UHP metamorphic orogen in Eastern China

Abstract

Corresponding to the Early Mesozoic continental subduction between the North China Block (NCB) and the South China Block (SCB), the Tongbaishan–Hong'an–Dabieshan–Sulu massifs are famous for their HP–UHP metamorphism. More than 50% of the HP–UHP Orogenic Belt was significantly reworked by Early Cretaceous extensional tectonics. This Early Cretaceous event with a fast cooling period, at 130–120Ma, superimposed on the Early Mesozoic HP–UHP orogenic belt and intensively changed the architecture of this orogen. Each individual segment documents different Early Cretaceous extensional structures, namely the central Tongbaishan domain is a metamorphic core complex (MCC) represented by an A-type non-cylindrical antiform; the central Dabieshan domain is a typical Cordilleran-type migmatite-cored MCC; the Southern Sulu UHP domain is a “wedge-shaped” structure exhumed by a simple detachment fault. These late stage extensional structures expose the previous HP–UHP orogenic belt as fragments along the NCB–SCB boundary. The geodynamic setting of this Early Cretaceous extensional tectonics along the HP–UHP orogen is a part of a 1000km-scale crustal extension belt that is widespread in eastern Eurasia continent from Trans-Baikal to the central part of SCB. Convective erosion or delamination of the mantle lithosphere might be considered as a possible mechanism for mantle removal.