Post‐Collisional Ductile Extensional Tectonic Framework in the UHP and HP Metamorphic Belts in the Dabie‐Sulu Region, China

AbstractThe present‐day observable tectonic framework of the ultrahigh‐pressure (UHP) and high‐pressure (HP) metamorphic belts in the Dabie‐Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino‐Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran‐type metamorphic core complex, in which at least four regional‐scale, shallow‐dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P‐T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie‐Sulu region was achieved, at least in part, by non‐coaxial ductile flow in the multi‐layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite‐ to greenschist‐facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.