The discovery of Dazaohuogou-Wanbaogou Late Permian epicontinen-tal arc volcanic rocks in Eastern Kunlun Mountains and its significance

The material composition in Eastern Kunlun area is complex with long tectonic evolution history. The building materials have been preserved to record geological events that have occurred since the Paleoproterozoic. The orogenetic phase from Middle Devonian to Middle Triassic was particularly important in many ocean-land transformations, thus being a major period of magmatism and mineralization in the Eastern Kunlun area. For a long time, records of Permian volcanic rocks in the Eastern Kunlun area were lacking. 1:250000 regional geological survey was carried out recently in Dazaohuo area and, as a result, a volcanic rock group of inter-mediate-acid, high potassium, calc-alkaline series was discovered, and U-Pb age of zircon in the subrhyolite-dacite was obtained through LA-ICP-MS, which is 254.7±0.6Ma. The eruption of volcanic rocks under the continental margin arc environment was newly named Late Permian Dazaohuogou Formation to accord with section research and regional correlation. The Dazaohuogou For-mation mainly located in the Dazaohuogou-Wanbaogou area is strictly controlled by southern Kunlun fracture, with the outcropping area more than 74km². This discovery not only provides definite evidence for the existence or nonexistence of Permian volcanic rocks in the Eastern Kunlun magmatic arc but also fills the gaps in Late Permian volcanic strata. The northward subduction of Kunnan Ocean started from Permian in Eastern Kunlun area, and formed huge collision-type granites. Volcanic rocks of the Dazaohuogou Formation imply that East Kunlun area was still in the regional extrusion phase in Late Permian.