High‐temperature geochronology constraints on the tectonic history and architecture of the ultrahigh‐pressure Dabie‐Sulu Orogen

Abstract

New U/Pb zircon and Th/Pb monazite ages are presented from the giant Sulu ultrahigh‐pressure (UHP) terrane. Combined with Sm/Nd ages, Rb/Sr ages, inclusion relationships, and geologic relationships, they help define the timing of peak recrystallization, the timing of subsequent amphibolite‐facies metamorphism, and the architecture of the Dabie‐Sulu suture zone between the collided Sino‐Korean and Yangtze cratons. The data indicate a ∼15 Myr record of UHP recrystallization, the first clearly documented for a giant UHP terrane; this requires that continental subduction in the Dabie‐Sulu orogen involved multiple UHP tectonic or recrystallization events. A 244–236 Ma “precursor” UHP event, seen only in the Dabie Shan, was followed by a second, ∼230–220 Ma “main” UHP event, which was itself terminated by a 220–205 Ma amphibolite‐facies overprint. Older eclogite‐facies events seen in the Qinling segment of this orogenic belt raise the possibility that these rocks have undergone (U)HP metamorphism three or four times, but at present, there is no geochronological evidence in the Dabie‐Sulu area to support this. The subduction of the lower, Yangtze plate did not proceed in a simple fashion: The ages of inherited zircon cores demonstrate that a ribbon continent of Yangtze affinity escaped subduction and became wedged against the Sino‐Korean plate hanging wall.