The Petrogenesis And Tectonic Setting Of The Late Carboniferous Volcanic Rocks From Jueluotage Area, Eastern Tianshan, NW China

The Late Carboniferous volcanic rocks are widespread in the area of Jueluotage,EasternTianshan Mountain,XinJiang.They are closely related with mineralization, also are one of thefocus on clousure of Paleozoic ocean basin and transformation for the Western Tianshantectonic system.Therefore, some meticulous research on the Late Carboniferous volcanicrocks of this tectonic belt has important scientific meaning for better understanding theocean-continent transformation process of the South Tianshan Ocean, which are representedby Ophiolitic melange belt at the southern margin of Middle Tianshan.At the same time, italso provides basic geologic information on Late Paleozoic volcanic metallogenic background.On the basis of previous studies,this paper take the Late Carboniferous volcanic in the middleof Jueluotag tectonic belt as the research object,by systematically studying the aspects ofpetrography, geochemical and geochronology, we determined the rock association,stratigraphic sequence and variations of Qishan Formation,Qi’eshan Formation,WutongwoziFormation,established a regional geochronological framewock, and then discussed thepetrogenesis of the volcanic rocks and its tectonic setting, constrained on the closure time ofthe South Tianshan Ocean. The main conclusions are following:1.The Volcanic rocks of Qishan Formation in the south of Tuwu are almostintermediate-basic volcanic lava,and a small number of pyroclastic rocks folders;The Volcanicrocks of Qi’eshan Formation in the south of Nanhu is mainly andesite, followed by dacite,basaltic andesite, basalt,and Basalt less content, the southern section is WutongwoziFormation,which is mainly made up of basalt. Wutongwozi Formation in the northern ofYamansu area is still mainly made up of basalt,and this kind of basalt is mainly to rapidcooling and crystallization in the underwater environment.2.Regionally,the Late Carboniferous volcanic rocks on the north of Kangguer Fault havemafic decreasing extent and eruption facies growing trend from west to east.The volcanicrock of Wutongwozi Formation is stillbasalt formed in the underwater environment.3.Geochronology study showing that,the age of Qishan Formation is299.4±7.7Ma,theage of Qi’eshan Formation is306.1±4.9Ma,both of them were formed in the late of the LateCarboniferous.4.The Late Carboniferous volcanic rocks in Jueluotage area are classified intosub-alkaline.All basalts are classified into tholeiitic series,intermediate rocks are mainlyclassified into ca-alkaline magma series.The REE patterns showed a slight rightward-type or flat type.They are relatively enriched in LILE,and relatively depleted in HFSE, have acertain degree of Nb, Ta and Ti negative anomalies. And it’s showing intraplate basaltcharacteristics affected by crustal contamination5.The similarities of REE and trace element normalized pattern and trace element ratiosbetween basalt-basaltic andesite, andesite, dacite-rhyolite suggest that they derived from asame magma source.Basalt magma may most likely come from the lower part ofasthenosphere.Basalt source regions are original garnet lherzolite zone,and the degree ofpartial melting is relatively high,is about10%.6. The Late Carboniferous volcanic rocks of Jueluotage area formed in a continentalextensinal environment.Therefore,Jueluotage in eastern Tianshan have stay in intraplateevolunary stage.