Chronology,Geochemistry And Petrogenesis Of The A-type Granites From The East-Alataw Mountain,Western Tanshan,Xinjiang

The Alataw mountain in Xinjiang is located in the northwest Tianshan.It is an important part of the Central Asian orogenic belt,and lots of Late Carboniferous-Early Permian granite are widespread in this area.At present,there are still some disputes over the genetic type,magma evolution process and perogenesis of granites in the Alataw mountain area of the Western Tianshan.There are large amounts of Late Carboniferous to early Permian A type granites around the Junggar basin of northern Xinjiang.It is ambiguous that whether there are contemporaneous A type granites developed in the Alataw mountain.Additionionly,the(⁸⁷Sr/⁸⁶Sr)_i of granites from the Alataw mountain are higher than the contemporaneous granites from East Tianshan and West Junggar,but their?_Nd?t?are lower.Whether these differences are related to the Precambrian basement in Western Tianshan orogenic belt?What role might the Precambrian basement have played in the formation of Alataw mountains granites?This paper focuses on granites in the Kongwusayi intrusion and the Wutubulage rhyolite in the eastern of Alataw mountain.The mineralogy,geochronology,geochemistry studies have been carried out on granites and rhyolite.Combined with the previous research and the results of this paper,the rock types,geochronology magmatic evolution,petrogenesis and tectonic significance of the Kongwusayi granites and Wutubulage rhyolite have been stuied.This paper mainly obtains the following conclusions:1.The Kongwusayi intrusion have been mainly composed of granite porphyry,monzonitic granite,coarse-grained K-feldspar granite and the later fine grained K-feldspar granite.Among of them,the granite porphyry formed in 293.3±4.0Ma;the monzonitic granite formed in 293.1±3.6Ma;the fine grained K-feldspar granite formed in 293±3.7Ma.The granites from Kongwusayi intrusion were formed from Late Carboniferous to early Permian.2.The granite porphyry,monzonitic granite,coarse-grained K-feldspar granite and the fine grained K-feldspar granite of Kongwusyi,and rhyolite of Wutubulage are enriched in Zr,Hf and rare-earth elements,and depleted in Ba,Sr,P,Ti and Eu.They have high total K₂O+Na₂O,Fe*value,TiO₂/MgO ratio,and Ga/Al ratio.The biotites in granites and rhyolite belongs to iron-enriched mica.The geochemical and mineralogical characteristics of granites and rhyolite are similar with A2 type granite.The composition of geochemistry and amphibole in monzonitic granite indicate that it has the characteristics similar with aluminous A-type granite.3.From the granite porphyry,the monzonitic granite,the coarse-grained K-feldspar granite to the fine grained K-feldspar granite in the Kongwusyi intrusion,the negative Eu anomalies become more obvious.The depletion of Ba,Sr,P,Ti and the enrichment of Rb,Th,U has gradually increased,the magma temperature gradually decreases,and alkaline feldspar contain higher and higher sodium.The above characteristics show that the granites in Kongwusyi intrusion are produced by magma evolution of the same parental magma.Compare with Kongwusayi granite,Wutubulage rhyolite crystallized in a higher temperature condition suggesting that rhyolite was formed by the later magmatism event.4.Both the Kongwusayi granites and the Wutubulage rhyolite show high?_Nd?t?and high Y content,lower Mg^#.Mg^#values in biotite are lower than 6%.The study of isotopic geochemical and mineralogical characteristics show the Kongwusyi granites and the Wutubulage rhyolite may be derived from the young basaltic crust in the post-collision extension setting and formed in lower pressure,high temperature and lower oxygen fugacity condition.Besides,the Precambrian crustal materials were involved in the magma source.Further more,increasingly ancient crustal have been involved in the formation of granites from the granite porphyry to the coarse-grained K-feldspar granite.Because more Precambrain crustal materials were involved in the formation of western granites than the eastern part,the western granites have higher A/CNK and contain alumina-peraluminous minerals like muscovite.The western granites in the Alataw Moutain may belong to aluminous A type granite.