The Geological Components And Tectonic Evolution Of South Tainshan, Xinjiang

South Tianshan is located in the junction of Tarim and Kazakhstan plates as the east extension in the Chinese territory of the Urals - South Tianshan orogenic belt which is a typical Paleozoic orogenic belt. South Tianshan is a Paleozoic collision zone which was developed from a broad ocean basin between the Tarim and Kazakhstan plates, composed of two ophiolite belts and their surrounding continental rocks and ancient crystalline basement. The tectonics and evolution of South Tianshan have always been the focus of the geological study. The reconstruction of the tectonics and evolution is the key to solving the plate tectonic activity and resource evaluation of South Tianshan Region.Based on the theory of plate tectonics and recent regional geological survey results, the author focused on the studies of geology, chronology and petrology of the ophiolite, intrusive rocks and volcanics in South Tianshan. Coupled with stratigraphy, tectonics and paleomagnetism, the author reconstructed the history of geological evolution and the tectonic features of South Tianshan.South Tianshan is a complicated orogenic belt composed of geological units of various ages, bounded by the fault named Nalati Mountain South in the north, by South Tianshan Fault and Tarim Basin in the south, composed of Eerbin Mountain, Haerke Mountain and Hula Mountains. Many dextral shear zones developed among the three mountains. Each mountain occurs as a normal fan style in profile and the whole South Tianshan forms a large fan tectonic style.The author conducted field geological survey and indoor comprehensive study on the Southern Tianshan ophiolite belt and the regional geology including pretrology, chronology and tectonic environment of South Tianshan and proposed that the south Tianshan ocean basin had already developed into substantial scale in the Late Sinian and closed in late Carboniferous. There exist two ophiolite belts, one in north and one in south, both represent the relics of the oceanic crust. The South ophiolite belt can be divided into two sub-belts in the North and the South, the North Belt starts from Kule lake through Tielimaidaban, Hulagou extending to Yanqi Basin; The south belt starts from Kyrgyzstan and enter China at Aheqi, through Mishibulake, south Hulashan to the east. This sub-belt contains the main ophiolite in the South Tianshan, which can be correlated to the ophiolite belt at south Fergana section in former Russia. The author thinks that may exist Kuergan oceanic island which separate the south and north ophiolite belts. The island arcs and the kinetics both support that the two ophiolite belts are the oceanic crust relics after the south oceanic basin was subducted into north and south.This study presented Silurian acidic intrusions through SHRIMP zircon U-Pb dating (436±Ma) which was thought to be Hercinian intrusions. Petrology and geochemistry studies indicate there were early Silurian intrusive rocks which has the features of syn-collision orogenic granite and there exist calc-alkaline intrusions at ages 370±7Ma and 366±8Ma in the Nalati mountains. Coupled with the calc-alkaline volcanics of late Silurian and Early Conbonniferous, the author proposed that the Nalati Mountain is a active continental margin in later Paleozoic.The author identified syn- and post-collision granites at about 300Ma in the Erben Mountains and proposed that the granites of Carboniferous in south Tianshan are mainly crustal sourced syncollision granite, related to the crust thickening and synchronized to the development of Carboniferous remaining oceanic basin with an age ranging between 300 and 340Ma. The Permian granites are post orogenic K-rich granites a t ages between 250 and 290Ma, related to post orogenic extensional environment.The author identified Nanmuzhaerte-Heiyingshan-Seriyakeyilake-Hulashan and Nalatishan have the same tectonic features and developed early Paleozoic syncollision granites and obtained an age of 387±8Ma using SHRIMP zircon dating for the granodiorite which was thought to be Carboniferous in age. is for a Middle Devonian calc - alkaline intrusion which is related to the plate subduction.Based on rock assemblages, rock chemistry and geochemistry characteristics, the author first presented that the region between Haerkeshan and Ererbinshan was an arc in late Silurian and early Devonian. As the result of the subduction of the south Tianshan oceanic basin to the Haerkeshan and Ererbinshan plate, volcanics and terrestrial clastics were developed at the Kaidu River in Devonian. These volcanics are mainly intermediate and basic volcanics and intermediate and acidic volcanics and are low K sub-alkaline series and calc-alkaline basalt series by rock chemistry and indicate arc volcanics by geochemistry. The intermediate and acidic volcanoclastics and acidic lava in the north Haerkeshan formed a Late Silurian and Early Devonian calc-alkaline volcanic belt.The oceanic crust relics at Heiyingshan and Hulashan are identified to be a volcanic assemblage of oceanic island type with an association of intermediate and basic lava and volcanoclastics, together with the deep sea sediments formed the oceanic crust relics at Heiyingshan and Hulashan. A lot of radiolarian has been found in the silicious rocks at the upper part of oceanic crust and was dated Early Devonian–Early Carboniferous.The author presented that there existed many small continents within the Paleozoic oceanic basin in south Tianshan which resulted into the coexistence of many oceanic basins and subduction and closure at different ages. In Ealrly Paleozoic, there were three parallel arc belts, Nalati, Haerkeshan-Eerbinshan and Seriyakeyilake -Hulashan arc belts from north to south. Nalatishan arc accreted to Middle Tianshan block at Yili in early Paleozoic, while the Seriyakeyilake -Hulashan accreted to the north edge of Tarim Plate. In late Paleozoic, south rim of the Nalatishan and Seriyakeyilake arc entered into stage of active contimental margin.Based on systematic studies of rock components of south Tianshan, the author proposed that the ophiolite complex at Heiyingshan- Seriyakeyilake is the suture zone of Tarim plate and Hasakeshitan plate and classified the tectonic units for middle and south Tianshan and presented the orogenic model for south Tianshan and reconstructed the evolution history. The author proposed that the south Tianshan ocean basin was a part of the ancient Asian ocean, together with other oceanic basins in the north of the ancient Asian ocean, south Tianshan oceanic basin broke up in Sinian into many island arc and accreted to lateral plates and closed in late Carboniferous.