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

[ 1] 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 similar to 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, similar to 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.