Evolution Characteristics Of Bogda-balkun Intracontinental Rift In Carboniferous-early Permian

East tianshan mountain occupies an important position in the study of tianshan orogenicbelt, Bogda-Balikun-Harlik mountain which located in the north of Tuha basin in Easttianshan has the vital significance in the study for solid mineral, oil and gas, basin coupling,the earth dynamics research. In this paper, based on several research projects, combiningprevious research material, through a comprehensive analysis of the ancient sedimentaryenvironment, the geochemistry characteristics of volcanic rock, in detail discussed the riftevolution characteristics in Carboniferous-early Permian, specific content as follows:Preliminary confirmed that the structure attribute of Bogda–Balikun mountain inCarboniferous-early Permian is Intracontinental rift, different from the Harlik-Dananhu arcin the south and Yilinhabierga Residual ocean basin in the west, it was a collision-induced riftcoused by the closing of Kelamaili-Maiqinwula ancient oceanic basin in the northeast part ofreasch area which was in stretching stage after the collision.Through contrastive geochemical analysis towards bimodal volcanic rocks that widelydeveloped in Bogda–Balikun mountain, basalt and rhyolite has the comparable major andtrace element characteristics, Sr-Nd-Pb isotope characteristics, the basalts were derived from adepleted mantle,while the associated rhyolites were formed by fractional crystallization of thebasaltic magma in early stage,and resulted obviously from partial melting of lower crustalmaterials by underplating of basaltic magma or mantle diapirism in the late stage. In thisprocess, was contaminated by Early Paleozoic arc.The basalts belonging to tholeiitics seriesmostly, alkali basalts series only found in the late stage, REE distribution pattern was flat orslightly enriched in LREE, no Eu anormalies, slightly enriched in incompatible elements,relatively depleted in Nb-Ta-Ti. And have great change in Sr-Nd-Pb isotopecharacteristics,with positive εNd(t), Rhyolite were alkaline series, and change to calc alkalineseries, High in potassium calc-alkaline series, REE distribution pattern was typically enrichedin LREE, Eu anomaly is not obvious in early stage, yet great in the late stage, primitivemantle standardization of trace element distribution pattern were strong enrichment ofincompatible elements, with a consistent negative anomaly of Sr, P, Ti and active elements(Rb, Ba, K) abundance of intense change, the Sr-Nb-Pb isotope changes greatly, but havesimilarity with basalt, epsilon Nd (t) values between+5.0~+6.92, bigger than the basalt; Hasthe characteristics of continental intraplate acidic lava. Preliminary thought, since theCarboniferous-early Permian, the study area geochemical properties between different sections, different time is mainly due to the difference of crust thickness, as a result of thelithosphere, hyperplasia of early Paleozoic arc is caused by the contamination degree ofdifferent.The stage and Segmentation evolution characteristics of Bogda–Balikun rift wereanalyzed, and tried to recover the ancient rift environment pattern.