The Geochemical Characteristics And Significance Of Basic Rocks In Karamay Ophiolitic Mélange Rock In West Junggar,xinjiang

West Junggar is located in the southwest hinterland of the Central Asian orogenic belt and is a hot spot for studying the structural pattern of the Central Asian orogenic belt.This paper focuses on the Karamay Ophiolitic mélange as the main object,based on the petrology,geochemistry and Sr-Nd isotope to discuss the petrogenesis and tectonic environment of the ophiolite,combined with previous data,aimed at providing constraints on the tectonic evolutionary history in the Late Paleozoic in West Junggar.Karamay Ophiolitic mélanges are mainly distributed in the Baijiantan and Baikouquan areas in the Eastern Karamay from northeast to southwest.The rock components of the ophiolitic mélange include mantle peridotite,gabbro,pillow basalt and deep marine siliceous rock.The basalt of Karamay Ophiolitic mélanges belongs to the calcium-alkaline series,and its rare earth distribution pattern is similar to the OIB.The basalt is rich in Large Ion Lithophile elements?LILEs?.The spider diagram shows positive anomaliy of Sr and significantly negative anomalies of Nb and Ta.The gabbro of Karamay Ophiolitic mélanges belongs to the tholeiitic series,and its TiO₂ content is similar to that of the island arc volcanic rock.The rare earth distribution pattern of the gabbro is similar to the MORB.The gabbro is depleted in LILEs and is enriched in High Field Strength elements?HFSEs?.Basalt has high ratio of Nb/Yb and Zr/Nb,it derived mainly from enriched mantle and contaminate with a little depleted mantle source material.The(⁸⁷Sr/⁸⁶Sr)i ratio of the gabbro is close to the depleted mantle?0.703389?0.705889?and it has high positive?Nd values?+8.54-+10.00?,indicating that the gabbro was derived from the depleted mantle.Gabbro and Basalt are mainly formed by the partial melting.The Nb/La value of gabbro does not change as the value of Mg^#changes,which indicates that there was no obvious contamination of the earth's crustal materials during the formation process of gabbro.By REE simulation,we found that gabbro and basalt are the products of partial melting of spinel Iherzolite,but the degree of partial melting is different.The basalt plotted in the OIB area in the tectonic discrimination diagram,showing it was formed in the oceanic intraplate tectonic environment.It may be a fragment of the ancient ocean island from the overthrow.The gabbro has both MORB and IAT features,and may be formed in the island arc tectonic setting related to subduction.Therefore,the Karamay ophiolite melange is identified as SSZ type ophiolite and may have been formed in the back-arc basin affected by subduction.The previous data indicates that the formation time of Karamay ophiolitic mélange was between the Middle Ordovician and the Late Devonian.The Ophiolitic mélanges exists in Carboniferous strata in early Dextral transform compression deformation structures.In late Carboniferous epoch,due to the closed extrusion stress of West Junggar remnant ocean basin,the underlying ophiolitic mélange and residual oceanic crust are wedged into overlying strata of early carboniferous.