The Volcanic-sedimentary Characteristics And Tectonic Setting Of Devonian Rocks From Northeast Margin Of Tuha Basin In Eastern Tianshan

In this paper, Regarding the Devonian in East Bogda and Harlik as the object, northeast margin of Tuha basin in East Tianshan, we research research formation in geological characteristics, petrology and lithology, geochemistry and chronology by combining volcanic rock with sedimentary rock. And we achieved the following understanding.In East Bogda, the rocks combination of Devonian is composed of Dananhu Formation’ close terrigenous clastic rock mixing a small quantity of basic volcanic rocks-Tousuquan Formation’ close terrigenous clastic rock mixing a small quantity of siliceous rock and limestone-Kanguertage Formation’ medium-coarse terrestrial clastic rocks a small quantity of basic volcanic rocks. Its sedimentary environment reflects a regression process from bathyal facies, neritic facies, littoral facies to transitional facies, and its deposit sediment is from Karamori Mountain. In East Harlik, the Devonian is composed of Dananhu Formation’ volcanic rocks and pyroclastic rock in lower part and terrigenous clastic rock mixing a small quantity of limestone in upper part and Tousuquan Formation’ terrigenous clastic rock and pyroclastic rock mixing some volcanic rocks. them also reflects a regression process from neritic facies, littoral facies to tidal-flat facies, and its deposit sediment is from Harlik Mountain.We identified a set of early Devonian calc-alkaline dacite with the 397.5±4.7 Ma LA-ICPMS zircon U-Pb age and the Late Devonian tholeiite basalt-andesite with the 366.1±1.7 Ma LA-ICPMS zircon U-Pb age in East Bogda. We also confirmed early Devonian calc-alkaline intermediate-acid volcanic rocks with the 408.5±1.9Ma LA-ICPMS zircon U-Pb age and the Middle Devonian calcium alkaline basaltic andesite-andesite with the 391.6±7.5 Ma LA-ICPMS zircon U-Pb age. In general, the age of Devonian volcanic rocks in East Harlik is earlier than the Devonian volcanic rocks in East Bogda.The early Devonian Dananzhu Formation volcanic rocks’ REE abundance appear a rightly-oblique patterns type characterized by fractionation and trace elements featured with being rich with large-ion-lithophile elements and observably depleted high-field-strength elements. The intermediate-basic volcanic rock formatted in island arc environment by the mixture of the mantle wedge and subducting sediment partial melting and enriched. The magma could assimilated some crust materials on the way up. The intermediate-acidic volcanic rocks is the produc by crust refusion. The Middle Devonian Tousuquan Formation volcanic rocks also formatted in island arc environment with the similar geochemical characteristics to the volcanic rocks from Dananhu Formation. It formatted by mantle wedge partial melting, experiencing fractional crystallization and crust assimilation in rising. In East Bogda, the Late Devonian tholeiite basalt-andesite have a familiar geochemical characteristics with the mid-ocean ridge basalts.It is the product of asthenosphere rising and >5% partial melting in stretch environment. And the magma hardly be assimilating crust material, but had a crystal fractionation.The andesite associated with the basalt could formatted by the basalt differentiation.The formation and evolution of Devonian volcanic-sedimentary rocks from northeast margin of Tuha in East Tianshan had a close relationship with the continuous subduction of East Tinshan Ocean towards north in Neopaleozoic. It could be in last stage of Middle Devonian to preliminary stage of Late Devonian that the Kazakhstan Plate had connected with Siberian plate.