Volcanic Rocks Tectonic Setting And Source Rock Development Model In Batamayineshan Formation, Wulungu Area, Eastern Junggar Basin

Large Carboniferous oil and gas fields have been found in Shixi,Wucaiwan,Kelamei and other areas in the east of Junggar basin,indicating that the Carboniferous in the Wulungu area of Junggar basin has a broad prospect for oil and gas exploration.Carboniferous is an important period of structural system transformation in Northern Xinjiang,including Junggar basin.During this period,volcanic rocks developed on a large scale.The formation of the complex structural background and the distribution of volcanic rocks and sedimentary rocks are not clear enough,which seriously restricted the exploration of Carboniferous oil and gas in Junggar basin.In this paper,the volcanic rocks of Batamayineshan formation in the east of the Wulungu depression are studied,and the research results of Zhaheba,Baijiangou,Wulungu depression,Luliang Uplift and other areas for the volcanic rocks of the Batamayineshan formation are combined.By using the methods of chronology and geochemistry,the tectonic background and the geological characteristics of the volcanic rocks of the Batamayineshan formation in the Wulungu area are studied based on the analysis of the origin,the macro distribution and the formation environment of the source rocks in the Batamayineshan formation are analyzed,and the development model of the source rocks is established,which provides a favorable guidance for the exploration of Carboniferous source rocks in the Wulungu area.1.The formation age of volcanic rocks in Batamayineshan formation,Wulungu areaIn this paper,zircon U-Pb dating of the volcanic rocks of the Batamayineshan formation in the Takeerbasitawu area is carried out for the first time.The results show that 321.4±1.5Ma belongs to the Late Carboniferous.Based on the previous zircon U-Pb dating results of the volcanic rocks of the Batamayineshan formation in different locations in the Wulungu area,it is considered that the formation age of the volcanic rocks of the Batamayineshan formation is from the Early Carboniferous to the early Permian.2.Origin and tectonic setting of volcanic rocks in batamayineshan formation,Wulungu areaThe volcanic rocks of the Batamayineshan formation in the Takeerbasitawu area are mainly of medium basicity,belonging to the calc-alkaline series.The main elements have the characteristics of medium Mg#index,the high content of rare earth elements indicates that the original magma has undergone a certain degree of differentiation,the Harker diagram and the absence of negative europium anomalies indicate that the volcanic rocks have not undergone obvious plagioclase crystallization.The characteristics of trace elements show that Nb,Ta and other high field strength elements?HFSE?are enriched.Although they are similar to those of island arc basalts,they are more enriched in volcanic rocks than island arc basalts,and the Zr/Y values is significantly higher than that of island arc basalts,but they are mixed by lithosphere and crust in the process of magma rising,which makes them have island arc basaltic characteristics of rock.The original(⁸⁷Sr/⁸⁶Sr)_i values of the volcanic samples is similar to that of ocean island basalt?OIB?.The?_Nd?t?values indicates that the magma source area belongs to the depleted mantle,but the extent of the depletion of the magma source area is smaller than that of the magma source area forming the island arc basalt,which belongs to the post collisional basalt.Based on the results of previous studies on the tectonic setting of the Batamayineshan formation,it is believed that the volcanic rocks of the Batamayineshan formation in the Wulungu area were formed in the background of post-collision,because the plates previously in the state of compression changed to the state of extension,the thickness of the crust decreased,resulting in the asthenosphere mantle flowing up to the surface.3.Source rock development model of Batamayineshan formation in Wulungu areaThe source rocks of the Batamayineshan formation in the Takeerbasitawu area,Wucaicheng area and Baijiangou area are developed between the upper and lower volcanic rocks,and vertical interbedding of volcanic and sedimentary rocks;sedimentary rocks and volcanic rocks are distributed alternately in the plane.In this paper,it is considered that the fault activity under the background of post collision resulted in volcanic eruption and controlled the distribution of volcanic rocks,which in turn controlled the distribution of sedimentary rocks.The source rock is formed in the period of weak volcanic activity,which gathers water in the low-lying area between volcanoes and provides sediment accumulation space.The sedimentary environment is mainly delta-lake-swamp.The paleoclimate environment is warm and humid,which is conducive to plant growth.The reductive fresh water environment is conducive to the preservation of organic matter.The volcanic activity during the deposition has a positive effect on the formation of source rock.On the basis of this,the development model of source rock of"limited water body"in Batamayineshan formation of Wulungu area is established.