The Jinshajiang suture zone: tectono-stratigraphic subdivision and revision of age

Integrated study of rock assemblage, tectonic setting, geochemical feature, fossil contained and isotopic geochronology on the metamorphic mixed bodie s, exposed in the Jinshajiang suture zone, suggests that one informal litho stratigraphic unit, the Eaqing Complex, and three tectono-stratigraphic uni ts, the Jinshajiang ophiolitic melange, the Gajinxueshan Group and the Zhon gxinrong Group, can be recognized there. It is first pointed out that the r edefined Eaqing Complex might represent the Meso- to Neo-Proterozoic remnan t metamorphic basement or microcontinental fragment in the Jinshajiang area . The original rocks of it should be older than (1627 +/-192) Ma based on t he geochronological study. The zircon U-Pb age of plagiogranites within the Jinshajiang ophiolitic assemblage is dated for the first time at (294+/-3) Ma and (340+/-3) Ma respectively. The Jinshajiang ophiolite is approximate ly equivalent to the Ailaoshan ophiolite in the formation age, covering the interval from the Late Devonian to the Carboniferous. Dating of U-Pb age f rom basalt interbeds indicates that the redefined Gajinxueshan Group and Zh ongxinrong Group may be considered Carboniferous to Permian and latest Perm ian to Middle Triassic in age. In geotectonic terms the Jinshajiang suture zone is thought to be a back-are basin in the eastern margin of the Paleo-T ethys. This back-are basin started in the Late Devonian, and formed in the Devonian-Carboniferous. The collision event around the Perrnian/Triassic bo undary to the Middle Triassic led to the closure of the back-are basin and formation of suture.