The Geochemical Characteristics Of The Carboniferous Volcanic Rocks In The Wusunshan-tekes Daban Area,Yining Block

Carboniferous volcanic rocks are widespread in the Wusunshan-Tekes Daban area,Yining Block.Correctly understanding and appraisal of their tectonic setting is the key to reveal the closure of Paleozoic ocean basin and transformation process of tectonic regime.On the basis of previous work,this paper takes the volcanic rocks of Dahalajunshan Formation and Yishijilike Formation as the study objects,as an object of study,by systematically studying the aspects of petrology,petrography and geochemical,comparative study on the differences between two sets of volcanic rocks in the aspects of geological and geochemical characteristics,explored their different tetonic attributes,analysed source characteristics and genetic types.The above aspects provided new evidences for exploration of Late Paleozoic tectonic evolution in the western Tianshan Mountain.By comparative study on volcanic rocks of Dahalajunshan Formation and Yishijilike Formation,made the following understanding:1.The volcanic rocks of Dahalajunshan Formation are mainly composed of with basic volcanic and clastic rocks,followed by a small amount of rhyolite and clastic rock.Metamorphic rock very shallow,alteration is stronger,strong deformation of parts.Dahalajunshan Formation is unconformity contacted with in the overlying strata and by later tectonic reworking,local area is fault contact.2.The volcanic rocks of Yishijilike Formation are mainly composed of basic volcanic,rhyolite and clastic rock.They are weak deformation,more for monoclinic and have the characteristics of typical bimodal volcanic rocks.3.The volcanic rocks of Dahalajunshan Formation are mainly classified into calc-alkaline series.They are generally enriched in LILE and LREE,and relatively depleted in HFSE and HREE,have obvious Nb,Ta and Ti negative anomalies.The geochemical characteristics show that the volcanic rocks from the subduction of fluid/melt replacement of partial melting of the mantle wedge,and affected by different degree of crustal contamination.Combined with the tectonic environment discrimination diagram show the geochemical characteristics of active continental arc volcanic rock.4.The basalts of Yishijilike Formation are strongly enriched in LILE and LREE,and relatively depleted in HFSE and HREE,have obviousTa,Nb,Th and Sr negative anomalies.The basalts show?_Nd?t?=+3.45⁺3.55,that display the volcanic rocks may be from depleted mantle.The rhyolite has higher SiO₂,TiO₂,K₂O+Na₂O and extremely low,MgO style,the content of P₂O₅,TFe₂O₃,enrichment of LILE and LREE,loss of HFSE such as Nb,Ta,and the typical characteristics of the shell source magma.In combination with geochemical diagrams we believe the Wusunshan-Tekes Daban area has entered the stretching stage after collision in the late Carboniferous.5.Basaltic magma of Dahalajunshan Formation was derived from partly melting mantle wedge,which was metasomatized with fluid?melt?precipitated from subtractive sheet space.Andesitic magma was derived from the root of arc crust and affected by mantle wedge.Acidic magma was derived from the stable lower crust source,mixed with substances from mantle magma.Lithosphere delamination of orogen belt roots caused mantle material upwelling of asthenosphere in Late Carboniferous.Basaltic magma of Yishijilike Formation was derived from partly melting upper mantle substances.Felsic magma was formed by remelting of Precambrian basement,which caused by underplating of basaltic magma to the lower crust.6.The Wusunshan-Tekes Daban area of the Yining Block may experienced the period that island arc dived in early Early Carboniferous,back-arc basin extended localtensionally in lately Early Carboniferous?Akeshake Formation?,the north ancient Tianshan oceanic merged after Shanshan Movement,the system of post-collision rifted in Late Carboniferous,last it turned into intraplate rift valley in late Late Carboniferous or later.