Tectonic Framework and Evolution of South Tianshan,NW China

Chinese South Tianshan(South Tianshan for short)orogen between Tarim and Chinese Middle Tianshan(Middle Tianshan for short)has undergone complicate tectonic evolution,especially,the fore-arc accretion during the oceanic crust subduction of the ancient South Tianshan ocean under the Middle Tianshan volcanic arc.Traditionally,South Tianshan has been considered as a Hercynian fold belt,and mostly as the passive margin of Tarim.We summarize and discuss the data of radiolarian fossil,ophiolite(melange),high-pressure metamorphic belt,stratigraphy,deposits in the peripheral foreland basin and deformation in South Tianshan.The results indicate that:(1)The major part of South Tianshan is a large(ophiolite)melange with over 100km in width,which comprises dominantly of the accretionary wedge and also some collision complex;(2)South Tianshan is an Indo-Sinian orogen derived from the collision between Tarim and Middle Tianshan in the late Permian-Early Triassic;(3)Middle Tianshan overthrusted onto the northern margin of Trim and formed Kuqia peripheral foreland basin during the collision;(4)The ancient South Tianshan Ocean is a vast oceanic basin;(5)Middle Tianshan is the front volcanic arc of South Siberian archipelago;(6)Northern Tarim crust subducted intra-continently under Middle Tianshan in the N-Q,and formed the Northern Tarim neo-foreland basin;(7)Kuqia peripheral foreland basin and Northern Tarim Neo-foreland basin constitute a dual foreland basin of a continental collision orogen.