Paleozoic structural and geodynamic evolution of eastern Tianshan (NW China): welding of the Tarim and Junggar plates

摘要

Chinese East Tianshan is a key area for understanding the Paleozoic accretion of the southern Central Asian Orogenic Belt. A first accretion-collision stage, before the vlsean, developed the Eo-Tianshan range, which exhibits north-verging structures. The geodynamic evolution included: i) Ordovician-Early Devonian southward subduction of a Central Tianshan ocean beneath a Central Tianshan arc; ii) Devonian oceanic closure and collision between Central Tianshan arc and Yili-North Tianshan block, along the Central Tianshan Suture Zone; iii) Late Devonian-earliest Carboniferous closure of a South Tianshan back-arc basin, and subsequent Central Tianshan-Tarim active margin collision along the South Tianshan Suture Zone. A second stage involved: i) Late Devonian-Carboniferous southward subduction of North Tianshan ocean beneath the Eo-Tianshan active margin (Yili-North Tianshan arc); ii) Late Carboniferous-Early Permian North Tianshan-Junggar collision. The Harlike range, unit of Mongolian Fold Belt, collided with Junggar at Mid-Carboniferous, ending a north-dipping subduction. The last CAOB oceanic suture is likely the North Tianshan Suture Zone, between Yili-North Tianshan and Junggar. During the Permian, all the already welded units suffered from a major wrenching, dextral in Tianshan, sinistral in Mongolian Fold Belt, due to opposite motion of Siberia and Tarim.