The Indosinian Metamorphism, Magmatism And Formation Age Of Bunlunkuole Rock Group In Taxkorgan-Kangxiwar Tectonic Belt,Western Kunlun

The formation and evolution of West Kunlun orogenic belt is a quite complex process. The Kangxiwar tectonic belt is an important tectonic boundary of West Kunlun orogenic belt. Different types of high-pressure metamorphic rocks, great amount of granites and dedimentary stratums of different ages are distributed in this area, and function as the evolutionary product of West Kunlun orogenic belt. They preserve wealth information of Kangxiwar tectonic belt and can be used to interpret the evolution of West Kunlun orogenic belt, especially for the study of the evolution of Indosinian. This dissertation discusses the formation age, the properties and the evolution characteristics of Kangxiwar tectonic belt from three aspects, namely, Ta Xian (Taxkorgan, Tajik Autonomous County)-Kangxiwar tectonic belt, Indosinian granite and the major dedimentary stratum.The granulite exposed from the Ta Xian-Kangxiwar are selected to study. Based on the petrographic and mineral composition analysis, the phases of the metamorphic mineral are divided. Also, focusing on high-pressure politic granulite, high-pressure mafic and garnet pyroxenite, these three types of high-pressure metamorphic are phase diagram simulated by using Thermocale (3.3) program to construct the P-T pseudosection. By dividing the mineral phases and the P-T conditions of different phases of mineral defined from two aspects, and combined with geochronology, the P-T-t path is got. The P-T-t paths of the three types of rock are all clockwise metamorphic evolution path. In early retrograde metamorphism stage, P-T paths reveal isothermal decompression which reflected rock had overwent rapid exhumation process. In late retrograde metamorphism stage, temperature and pressure decrease P-T paths suggested three types of rock overwent amphibolite facies metamorphism and lifting once again.Based on zircon dating data of HP granulite, peak metamorphism age was between220-250Ma. The early retrograde metamorphism age was about220Ma and the late retrograde metamorphism age was about180-190Ma. The study of Ta Xian-Kangxiwar granite is mainly focusing on the exposed Indosinian granites from Shengli Bridge-Mazar-Thirty Miles Barracks-Kangxiwar line. Based on petrography, geochronology and geochemistry study, the nature of source rocks of these granites, forming conditions of these granites and the coupling relationship between these granites and the Kangxiwar tectonic belt are emphasized.Combined with previous studies, tectonic evolution process of Indosinian Granites along the Kangxiwar tectonic belt can be subdivided into four stages:The first stage may correspond to the subduction of oceanic crust stage and the corresponding age was about251Ma. The second stage may correspond to crustal thickening stage caused by the continent-continent collision and the corresponding age was about242Ma. The third stage may correspond to crust exhumation stage caused by subducting slab break-off and the corresponding age was during223-231Ma. The third stage may be dominated by post-collisional extension and corresponding time about during185-215Ma.The study of Ta Xian-Kangxiwar dedimentary stratum selects Bulunkuole rock group as the object which is the more contentious, more economic beneficial and also the most widely distributed in this area. From north to south, four profiles are chosen, namely, Tongchang ditch profile in Bulunkou, Ziluoyi iron ore profile, Ta Xian-Bandier iron profile and Zankan iron ore profile. The four sections are separated by hundreds of kilometers, covering most distributing area of Bulunkuole rock group. By measuring the profiles, identifying the material composition, selecting typical dating samples, limiting the forming ages of the profile strata and combined with the previous studies, the formation and evolution characteristics of Bulunkuole rock group are discussed. Combined with existing study, Proterozoic strata doesn’t exist in Bulunkuole rock group. The original divided Bulunkuole rock group contains Neoproterozoic, early Paleozoic and Permian strata. Neoproterozoic strata and early Paleozoic strata are exposed in the Zankan iron ore, Laobing iron ore, Ziluoyi iron ore profiles. Permian strata are exposed in the east of Ta County profile. Permian strata are exposed in the east of Ta County profile. Permian strata associated with high-pressure metamorphic rocks together may constitute the subduction collision complex. Based on material composition, stratigraphic sequence, Metamorphism and deformation characteristics, evolution and formation age of strata in Bulunkuole rock group, the. The original divided Bulunkuole rock group could be divide into two parts:Neoproterozoic-early Paleozoic stara and subduction collision complex.Combined study on High pressure granulite and Indosinian Granites in Kangxiwar tectonic belt, the evolution of Kangxiwa tectonic belt can be preliminary subdivided into four stages:The first stage was oceanic crust stage and corresponding age was about250Ma. The second stage was crustal thickening stage caused by continent subduction or continent continent collision and the corresponding age was about240Ma. The third stage was crust exhumation caused by subducting slab break-off and the corresponding age was during223-231Ma. The third stage was post-collisional extension and corresponding time about during185-215Ma.