Research Of Granite Formation And Tectonic Environment Of The Awulale Region, Western Tianshan Mountain,China

Granite, which records the deep geological events during its origin and evolution, is animportant part of the continental crust. Granite is one of the most important means tounderstand orogenic processes and crustal evolution, but also is one of the important contentsof the current continental dynamics. On the basis of previous data, this paper try to analyzethe rock type, genetic type, formation age, the source properties and the tectonic setting of thegranite in Awulale area by detailed geological survey, sample collection, petrographic andgeochemical study, LA-ICP-MS zircon U-Pb dating and Hf isotopic analysis. Combined withthese result, we discussed the contribution of the granitic magmatism to the crustal growthduring Late Paleozoic in Awulale area.Following understanding is mainly obtained:1. Combined the ages of the5granite samples obtained by LA-ICP-MS zircon U-Pbdating with previous data in Awulale area, we established the geochronological framework ofthe granite in this area, and divided the granitic magmatism into3stages. The first stage, earlyCarboniferous (350~320Ma), such as Chagangnuoer granite with343.3±3.7Ma and Zeketaigranite with324.1±3.3Ma. The second stage, late Carboniferous (320-300Ma), such asnorthwest Nuoer granite with304.2±5.6Ma and Wulangdaban granite with303.6±4.0Ma. Thethird stage, early Permian (300-280Ma), such as Yilanbasitao granite with291.8±3.7Ma.2. The Geochimistry proved that the granite is I-type in early Carboniferous, dominatedby I-type and A-type occurred in late Carboniferous，both I-type and A-type granite, withthe adakite output in early Permian, however.3. The Hf isotopic analysis showed that the granite in early Carboniferous yields a highpositive εHf(t), which may indicate the granite was the paitial melting of junenile crust. Thegranite in late Carboniferous yields both high positive and low negative εHf(t), indicate thatthe source region was partial melting from the juvenile crust and ancient crust. The granite inearly Permian yields a higher positive εHf(t), indicate the granite was mainly from the paitialmelting of junenile crust.4. Based on the results above, we discussed the tectonic settings of the granites in eachstage and the tectonic evolution mode of the Awulale area in late paleozoic. That can beconcluded as, continental margin arc in early Carboniferous, post-collisional extensionsetting in late Carboniferous, and continental rift in early Permian.