High pressure metamorphic belt in central Qiangtang, Tibetan Plateau: Progress and unsolved problems

A 500km-long high-pressure metamorphic belt has been documented in the central Qiangtang Block of northern Tibet, which is thought to have constituted the crucial geological archives of subduction and exhumation of Paleo-Tethys oceanic lithosphere. The high-pressure metamorphic rocks are mostly exposed along the Longmu Co-Shuanghu suture zone, and are composed of eclogites, blueschists, garnet-phengite-schists (Grt-Phn schists), and minor high-pressure mafic granulites. The eclogites in central Qiangtang are reported from Gemu, Guoganjianian Mt., Gangma Co, Baqing, and Mengku area, and occur mainly as blocks or small lenses in Grt-Phn schists. Apart from newly discovered Baqing eclogites, most eclogites from central Qiangtang Block are characterized by low peak temperatures and presence of lawsonite or pseudomorphs of epidote + paragonite, and their peak P-T results lie mainly in the lawsonite-eclogite field. The ages of most eclogites and blueschists from central Qiangtang block have been constrained as Late Triassic which are regarded as the results of closure of the Paleo-Tethys Ocean and following continental collision. Furthermore, the Permian high-pressure metamorphic rocks were also identified and their P-T-t paths revealed a complete evolutional history for the subduction erosion in response to the subduction of seamounts (or oceanic islands). Moreover, the discovery of Silurian high-pressure granulites in the central Qiangtang block indicates the existence of a previous collisional event on the northern margin of the Indo-Australian Gondwana. Hence, further comprehensive studies of the high-pressure metamorphic belt in central Qiangtang will provide valuable insights into the tectonic evolution of the north margin of Gondwana during the early Paleozoic and the opening and closure of the Paleo-Tethys Ocean.