Palaeozoic tectonic evolution of the Tianshan belt,NW China

The Chinese Tianshan belt is a major part of the southern Central Asian Orogenic Belt,extending westward to Kyrgyzstan and Kazakhstan.Its Paleozoic tectonic evolution,crucial for understanding the amalgamation of Central Asia,comprises two stages of subduction-collision.The first collisional stage built the Eo-Tianshan Mountains,before a Visean unconformity,in which all structures are verging north.It implied a southward subduction of the Central Tianshan Ocean beneath the Tarim active margin,that induced the Ordovician-Early Devonian Central Tianshan arc,to the south of which the South Tianshan back-arc basin opened.During the Late Devonian,the closure of this ocean led to a collision between Central Tianshan arc and the Kazakhstan-Yili-North Tianshan Block,and subsequently closure of the South Tianhan back-arc basin,producing two suture zones,namely the Central Tianshan and South Tianshan suture zones where ophiolitic mélanges and HP metamorphic rocks were emplaced northward.The second stage included the Late Devonian-Carboniferous southward subduction of North Tianshan Ocean beneath the Eo-Tianshan active margin,underlined by the Yili-North Tianshan arc,leading to the collision between the Kazakhstan-Yili-NTS plate and an inferred Junggar Block at Late Carboniferous-Early Permian time.The North Tianshan Suture Zone underlines likely the last oceanic closure of Central Asia Orogenic Belt;all the oceanic domains were consumed before the Middle Permian.The amalgamated units were affected by a Permian major wrenching,dextral in the Tianshan.The correlation with the Kazakh and Kyrgyz Tianshan is clarified.The Kyrgyz South Tianshan is equivalent to the whole part of Chinese Tianshan(CTS and STS) located to the south of Narat Fault and Main Tianshan Shear Zone;the so-called Middle Tianshan thins out toward the east.The South Tianshan Suture of Kyrgyzstan correlates with the Central Tianshan Suture of Chinese Tianshan.The evolution of this southern domain remains similar from east(Gangou area) to west until the Talas-Ferghana Fault,which reflects the convergence history between the Kazakhstan and Tarim blocks.