Material Composition And Determination Of Late Paleozoic Accretion Complex In Karamaili

Karamaili Accretion Complex zone,which is an important accretion complex zone in south margin of East Junggar Basin,locates in the ortheastern margin of Junggar Basin.Based on the detailed field investigation and related data of Karamaili,material composition,structure and evolution of the accretion complex zone will be discussed in this paper.Ophiolite and accretion complex in Karamaili accretion complex zone.This work mainly studies a series of accretion complex consisting of basalt,siliceous rock,andstone and tuff exposed in the form of tectonic slices in the accretion complex belt.The accretion complex in the study area can be divided into four parts: overlying rock sequence,exotic rock block,relic of the ocean crust and matrix.Only exotic rock block and matrix are studied in this paper.According to the characteristics of block assemblage,deformation and contact with each other,the exotic blocks are further divided into four blocks,and the matrix is composed of strong schistosomized sandstones.There are four types of accretive complex blocks in the study area,and asaltandesite blocks mainly show the nature of volcanic arc.The other three types of block provenances are mainly active continental margin rocks.According to the U-Pb zircon age of tuffaceous sandstone in tuffaceous sandstone block(peak age 393.2 Ma,latest age 328.0 Ma),the formation of tuffaceous sandstone block is not later than early Carboniferous.Combined with the characteristics of rock assemblage and age,the exotic rock blocks may be subducted northward by the Karamaili ocean basin,which involved the active continental margin strata in the north.Matrix is a geologic body with strong shear deformation,and its composition is mostly clastic,mainly sandstone.Its provenance area is the active continental margin.Based on the study of the accretion complex zone in the study area,a large number of bedding,structural foliation,lineation occurrence and deformation characteristics have been obtained.According to the cutting relationship between different structural foliations,the tectonic stages can be roughly divided into four stages.The first stage is formed in the early ductile deformation,the second stage is formed in the brittle highangle thrust during the collision and compression period,and the third stage is formed in the ductility during the extensional strike-slip period.Shear,the fourth stage formed in the late brittle low-angle thrust.During the Late Silurian-Early Devonian period,the Karamaili Ocean Basin opened.During the Devonian period,the mid-ocean ridge continued to expand on both sides and the ocean continued to grow.Large-scale subduction subsidence began to occur at the ocean margin.When the subduction subsidence was stronger than the midocean ridge expansion,the ocean entered a recession stage.The Karamaili Ocean ended in the late Early Carboniferous,during which the oceanic-continental transition took place.This paper holds that the controversy over the age of the formation of the Karamaili Ocean Basin is mainly due to the long-term expansion of the ocean basin and the emergence of new oceanic crusts,thus resulting in the diversity of the times.These results are not contradictory and have reference value,indicating that the Karamaili Ocean has been accompanied by the process of oceanic crust regeneration from the Late Silurian to the Early Carboniferous.