Tectonic Evolution And Mineralization Of The Western Kunlun Accretion-type Orogen

Based on the recent data of the regional geological surveying (1:250000) and previous studies in the western Kunlun orogen, the basic and economic geology were studied elaborately from field and geochemical studies. Magmatic arc is the key to study tectonic evolution of the western Kun orogen in this paper, and some tectonic units, such as Sinian-Cambrian rock assemblages of continental breakup, Ordovician-Silurian and late-Paleozoic accretionary wedges, and Mesozoic domes were defined. Geology, tectonic units, tectonic evolution and dynamical processes, and mineralization of the western Kunlun orogen were studied systematically, and the geological and resource map with a scale of 1:1000000 of this belt was compiled and modified, which can reflect the tectonic evolution and mineralization of the western Kunlun orogen objectively.The western Kunlun orogen is a complicated accretionary orogen, which was formed by continuous subduction of the Sinian to Cambrian Qin-Qi-Kun Ocean (proto-Tethys) to the Tarim plate in the Ordovician-Silurian, Devonian-middle Permian, late Permian-Triassic, and Jurassic in different mechanisms. Accretion southward along the southern margin of the Tarim plate took place and lasted more 500 Ma periods. This orogeny took place initially along the Kangxiwa-Subashi areas, paleo-ocean subducted northward and the trench retreated southward in these areas.The mineralization as an essential part of the orogen was controlled by the geological setting fully in the western Kunlun Orogen, and the special ore deposits were developed in different tectonic history. Mineral assemblage and ore deposit types also changed regularly during the orogen.The Rodinia Supper-continent broke-up in the Sinian-Cambrian and began spreading in the late-Sunian to form the proto-Tethys ocean. An archipelago between the Tarim plate and the oceanic plate in the south margin of the Kanxiwa-Subashi areas was developed, which consisted of Kulangnagu, Sangzhutage and Saitula micro-continental blocks, and Kegang, Kudi and Qimanyute small ocean basins and rifted basins or fractured ocean trough. Ore-forming system of the magnetite-hematite was produced, which was related to basic intrusion-volcano and volcano exhalative sedimentation.Ordovician-Silurian, proto-Tethys subducted northward along the southern margin (Kangxiwa-Subashi area) of the transitional type of blocks of the archipelago at a low dip of subduction zone, and the island-arc formed in front of the overriding plate. These island arcs became into island-arc chain slowly and collided with Tarim plate in the Late Ordovician along the Kegang-Kudi-QImanyute areas. Additionally, early Ordovician-early Silurian subduction-related granite belt and late Ordovician collision-related granites with hydrothermal vein- and skam-type Fe-Co deposits and 'Hetian' jade deposits respectively were formed during this subduction-accretion. The granite belt related to subduction became younger southward. Accretionary prism was formed and progressively widened along the trench in the forearc area;mineralization was related to the pelagic sediments of this prism, which consists of Fe- riched mudstone and Fe-Cu-Pb-Zn deposits bearing Mn-Ni-Co. This prism is the source bed of Mesozoic mineralization.In the Devonian-Permian, paleo-Tethys subducted northward continuously, but the dipping angle of downgoing plate became steep and the trench-arc system was formed. Arc-continent collision took place in the mid-Permian, which is the second accretion orogen in the western Kunlun. Late Paleozoic island arc has the characters of continental margin arc but different from the early continental arc. Early Paleozoic accretionary wedge became into the basement of the late Paleozoic island arc. The accretionary prism consists of Flysh and seamount (basalt and limestone) respectively, were formed in the forearc area;back spreading took place between the early-Paleozoic accretionary wedge and island arc to form the Subashi small ocean basin within the Kangxiwa-Subashi tectonic belt. The Kungaishan, KUerliang and Aqiang rifted basins were formed along the suture between early-Paleozoic island arc and Tarim plate. These basins are equal to the three proto-microblocks, and are important Cu and Pb-Zn mineralized belt. Five types of mineralization were formed within them.In the late Permian-Triassic, the extension of the Tethys ended but became into a remnant ocean basin, and the Gondwana continent moved northward. Then, Trissic remnant basin was filled by clastic rocks and folded, and the ocean became into continent. Accretionary orogen ended in the western Kun orogen.In the Jurassic, early to late Paleozoic accretionary wedge and the Bayankalashan Group in the south of the Kangxiwa fault uplifted and were lack of deposits. However, deep tectonic activities were continuous. The downgoing oceanic crust and sediments were melted in the deep and plutoned into the Paleozoic accretionary wedge to form Triassic-Jurassic granitoid belt with huge scale in the western Kunlun orogen. Oceanic crust partly melted to form I-type granitoid, which associated with S-type granitoid formed by deep-water sediments. Porphyry Cu(-Mo)deposits, and rare-earth and related rare metal resources were formed by I- and S-type granitoid respectively. Synchronically, Muji-Tashikuergan, Kangxiwa, and Huangyangling domains and abundant Fe-Cu-Pb-Zn-Au-Ag-Sb mineral resources were formed by regional metamorphism of the early Paleozoic accretionary prism. The mineral deposits show distinctive metallogenic zoning and different metamorphic grade formed its relatively mineral deposit. Mineralization controlled by plutons and domes is the peak metallogenic epoch in the western Kunlun orogen.