Study On Geochronology,geochemistry And Petrogenesis Of Volcanic Rocks From Yamansu Formation Of Southern Part Of Aqi Mountain Of Jueluotage Tectonic Belt Within Eastern Tianshan, Xinjiang Province

The Yamansu Formation occupied in southern part of Aqi mountain within Juluotage tectonic belt of Eastern Tianshan,and its age and petrogeness as well as tectonic setting are paradoxical.This thesis takes volcanic rocks from Yamansu Formation as study object,using petrology,zircon LA-ICP-MS U-Pb ages,whole rock geochemistry and Sr-Nd isotope geochemistry,our aims are constraining the age,petrogeness of those volcanic rocks as well as its tectonic setting.The volcanic rocks from Yamansu Formation in the study area are mainly composed of andesite,decite and rhyolite as well as corresponding compositional volcaniclasical rocks,with a small amount of basalt.Zircons from the main rocks?andesite and rhyolite?are euhedral-subhedral in sharp,display fine-scale oscillatory growing zoning,and have high Th/U ratios?0.44¹.53?,indicating a magmatic origin.The geochronological results indicate that these volcanic rocks fromed in the Early Carboniferous to Late Carboniferous?318.6³24.4Ma?.Geochemical date indicates that all of the volcanic rocks has the following characteristics:Acidic rocks range in the series of middle potassic calc-alkaline,whereas andesite and basalt range in the series of high potassic calc-alkaline.The REE distribution pattererns are right deviated,significant fractionation of light and heavy rare earth elements?LREE/HREE=2.91⁹.92?,They are all enriched in large ion lithophile elements?Rb?Ba?K?La?Ce?and relatively depleted in high field strength elements?Nb?Ta?P?Ti?.The(⁸⁷Sr/⁸⁶Sr)_i values and?_Nd?t?values range from 0.70401 to 0.70636 and 4.14 to 7.21,respectivelly.In conclusion,all these evidence indicates that the primary magmas of those mafic rocks generated by the partial melting of the depleted mantle wedge metasomasised by subduction fluids,whereas the primary magmas of these acidic rocks are generated by partial melting of the juvenile crustal material.Combined with the previous research results,suggesting that the primary magma of those early Early Carboniferous to early Late Carboniferous vocanic rocks from the Yamansu Formation within the southern Aqi Mountain area formed in continental margin environment during the subduction of the Paleo-Asian Ocean plate beneath the middle Tianshan plate.