The Geochemical Characteristics And Tectonic Setting Of The Volcanic Rocks Of The Dikaner Formation, Eastern Tianshan

The Jueluotage area of East Tianshan Mountain, is one of the important tectonic metallogenic belt in China. The intense magmatic activities in the late Paleozoic not only provide a material source for the mineralization, but also an important record of the geological tectonic evolution in the Tianshan Mountains. The Carboniferous volcanic activities is particularly widespread, but the formation environment remains controversial. This is a direct result of the of Tianshan tectonic system in the late Paleozoic evolution characteristics of views. The volcanic rocks from Dikaner Formation display east-west zonation within the metal logenic belt, and were controlled by Aqikekuduke and Yamansu faults in its south and north respectively. The significance of volcanic rocks that volcanic geological characteristics to understand the study area, the environment and other aspects of the formation and solve the tectonic setting of the East Tianshan Carboniferous and Jueluotage with ancient ocean basin closing time, during the Paleozoic restore ancient Tianshan ocean tectonic evolution.On the basis of previous studies, we choose the volcanic rocks of Dikaner Formation as our research object, after find out the temporal and spatial distribution of the volcanic rocks, combined with regional geological data and the achievements of the predecessors, through in-depth study of petrography, geochemistry method, and the geological profile to determine the volcanic rock assemblages, stratigraphic sequence and eruption rhythm, volcanic rocks of the petrogenesis and tectonic environment analysis, shows its limitations significance for ancient ocean basin closed. And we have made the following conclusions:1. The assemblages of volcanic rocks from Dikaner Formation are made of basaltandesite- dacite- rhyolite and intermediate-acid pyroclastic rock. According to the lithological characteristics and profile can be seen in the Dikaner Formation set parallel unconformity on Yamansu Formation. With the explosive facies, overflow facies and sedimentary facies rock ratio can also explain the Dikaner Formation more active volcano pits.2. The volcanic rocks of Dikaner Formation belong to sub alkaline rocks of calc alkaline series, and with calc alkaline series evolutionary trend, which are mainly the medium and high potassium calc-alkaline series. Geochemical characteristics of major elements show a good correlation between SiO2 and the other oxides; and the positive correlation between Na2 O and K2 O was not obvious. The rocks showed LREE enrichments and right-trending affinities, with increasing negative Eu and clear differences between LREE and HREE characters from mafic to felsic rocks.3. In the geochemical characteristics of trace elements, volcanic rocks mainly show the relative enrichment of LILE, and the relative loss of HFSE, Basalts and andesites have more consistent trace element enrichment and loss, The rhyolite is significantly enriched in Rb, Ba, Th elements, with negative anomalies of Nb, Ta, Ti, P, Sr elements.4. In the petrogenesis and Dikaner Formation should source from partial melting of a depleted mantle wedge, through the metasomatized by subduction fluids, and there is a limited role of crustal contamination in magma rising process of evolution. Andesites and basalts have similar geochemical characteristics, which may explain the same magma source, suggesting that the causes of andesite is products of cogenetic basaltic magma evolution, but also by a certain degree of crustal contamination effect. Rhyolite genesis of basaltic magma produced by partial melting of mantle wedge to rise to the lower crust, heat transfer and top inhibition and differentiation, in the upper crust shaped growth zone of partial melting of the felsic and after partially molten magma and assimilation mixed dyeing effect and fractional crystallization, spray the surface formation of rhyolite.5. Dikaner Formation volcanic rocks formed in subduction under the environment of the continental margin arc environment, using age data analysis, defining the Kangguer ocean closure time should be later than the Late Carboniferous early.