The Material Composition,Structural Deformation And Geological Significance Of Kobita Bea J Bai Bass Tao Paleozoic Accretionary Wedge,Qinghe County,Xinjiang,China

The study area is located in Kobita Bea J Bai Bass Tao area of Qinghe County ofXinjiang Altai, tectonic location is in the Siberia plate and Kazakhstan-Junggar plateconvergence zone, which belongs to Ertix subduction accretionary complex belt. According tothe development stage of this work and regional geological survey and comprehensive study,since the Ertix Eastern Mayinebo ophiolite belt to Caramaili ophiolitic melange belt, the maindevelopment of a geological body composed of Paleozoic accretionary complex. The researchobject of Kobita Bea J Bai Bass Tao accretionary wedge exposed in the Mayinebo faultbelt,which is a typical small accretionary complex of the most northern accretionary complex.According to the composition and characteristics of deformation of the accretionarywedge， which can be divided into five rock sheet. The first sheet is flysch and clastic rocksmetamorphosed; the second sheet is shallow metamorphic ocean deep-water sedimentary rock;the third sheet is the accretionary melange which containing ophiolite fragments; the fourthsheet is abyssal sediment; the fifth sheet is accretionary melange containing island arc rocks.Accretionary wedge material happened weak metamorphism and strong deformation, thetectonic deformation is mainly thrust imbricate structure, with the characteristics of rockwedge hyperplasia.In the accretionary wedge, through the study of rock, petrology, petrography, shows thatthe tectonic setting is active continental margin environment. At the same time the basaltblocks and metamorphic basalt blocks are distributed in the accretionary wedge, geochemicalanalysis showed that the volcanic rock had the feature of ophiolites, oceanic island volcanicrock, island arc volcanic rock, formed in the back-arc basin, oceanic intraplate environment aswell as the old block edge. Using the LA-ICP-MS method to obtain the U-Pb age of404.6±2.9Ma in the zircon of gabbro of ophiolitic melange, indicated that the area exist back arcbasin expansion effect in the early Devonian. Combined with previous research results in thebelt, Regional subduction-collision orogenic activity should be mainly occurred in the early-middle Devonian, then the region into post-collision stage in the late Devonian, therefore theaccretionary wedge should be formed in early middle Devonian.By observing the relation of contact in the field, outcrop geological body, deformationand metamorphic characteristics, Internal components of accretionary wedge like networknode distribution, tectonic deformation is strong and complex, formed a series imbricatethrust nappe structure from north to South, with features of the accretionary wedge. The early formation of accretionary wedge include inclined fold, overturned fold, homoclinal fold withsubduction tectonic deformation, shaft side leans to the north, from north to south, thedevelopment degree and close degree of fold decline, reflecting the accretionary wedgeformed by hyperplasic process from the north to the South and the deformation of differentlevels. Analysis of macro and micro structural deformation and the petrofabric analysis showthat the region experienced a strong shear sinistral ductile deformation later, formed theductile shear belt with mylonite developed extensively in accretionary wedge. Combining theresults of previous studies, the peak period of the occurrence of the regional large-scaleactivities should be290~270Ma.Based on the comprehensive analysis of regional data and the results of study area, theaccretionary wedge of study area is part of Altai-Junggar typical type of orogenic beltin thesouthern margin of the Altai orogenic belt, shown by the characteristics form the north to theSouth hyperplasia. According to the characteristics of the accretionary wedge material, showthat the accretionary wedge formed in an environment of Paleozoic back-arc basin, ceaselesshyperplasia in the southern margin of the Altai block, and the formation of subductionaccretionary complex in the middle-late Devonian.