ORIGIN OF CHINESE TIANSHAN BY ARC-ARC COLLISIONS

Four tectonic units are recognized in Chinese Tianshan: (1) North Tian shan Melange, (2) Middle Tianshan Arc, (3) South Tianshan Melange, and (4) Kelpin/Kuruktag Fold Belt. The Middle Tianshan and Kelpin/Kurukta g were early Paleozoic relic arcs, when the basement of Kunlun was the foundation of an outer volcanic arc on the ''southern underbelly'' of Asia. South Tianshan was a back-arc basin between the two relic arcs, and North Tianshan was a part of the Junggar Basin. Collapse of the S outh Tianshan Back-Arc Basin started in Ordovician, and its consumptio n led to the Devonian collision of the Middle Tianshan and Keipin/Kuru ktag Arcs. The basement and sedimentary cover of Middle Tianshan were thrust southward during late Paleozoic above the South Tianshan Melang e and the Kelpin/Kuruktag Fold Belt. The North Tianshan Melange is a l ate Paleozoic accretionary wedge on the northern margin of the Middle Tianshan Arc, when the ocean lithosphere of the Junggar Basin was subd ucted southward down the Benioff Zone of that active margin.