Study Of Karamaili Ophiolite Complex And Jiangbasitao Formaition Volcanic Rocks In East Junggar Of Xinjiang

The Karamaili ophiolite complex lies in North -east of Junggar basin in Xinjiang.It extends from Qinshuiquan to Solun mountain and Hegen ophiolite.It's strike is North-east and it has 150km length and 5-15km wideth.There are much Carboniferous System in the ophiolite region,including terrigenous elastic rocks,volcanoclastierocks and lava volcano. The typical unit of layer is Jiangbasitao formation.The Karamaili ophiolite complex in East Junggar of Xinjiang province is composed of metamorphic peridotite,gabbro,diabase and basic lava.LA—ICP—MS ziron U—Pb dating of gabbro from the Karamaili ophiolite suggests an isotopic age of 329.9±1.6Ma,which indicates that the Karamaili ophiolite occurred in the Visean of Early Carboniferous.The basic lava and gabbro in Karamaili ophiolite fragment show fiat patterns in chondrite-normalized REE diagram and primitive mantle—normalized trace elements diagram with lwo LILE abundance and no characteristic of IAT and OIB,These geochemical characteristics are similar with MORB and different from IAT and OIB,indicating that the ophiolite may be formed in middle ccean ridge,ombining with the study of field geological feature of Karamaili region,petrogeoehemistry and high—precision geochronology,can provide us an insight into the understanding:Karamaili ocean basin opened in early stage of Devonian and closed in the Serpukhovian of late Carboniferous.The relationship of Karamaili ophiolite and Jiangbasitao formation is structural contact. The formation could be divided into six rock unit.And there are typical bimodal volcanic rocks in the third,the fourth and the sixth rock units,which including alkaline basalt-acid voleanolastie rock-trachyte.Both of voealno lava are alkaline,while voleanolastie rock is subalkaline.The rocks show light REE enriched patterns in chondrite-normalized REE diagram and primitive mantle—normalized trace elements diagram with high LILE abundance and no exception of Eu.We could conclude that the formation formed in the post-collisional extension setting after Karamaili ocean basin closed and collision,through the study of geochemical characteristic and the chart of tectonic of volcanic rocks.With the LA—ICP—MS ziron U—Pb dating of trachyte(319.8±2Ma),we can draw a conclusion that Karamaili region had been a post-collisional extension settings after late stage of early Carboniferous.After synthetic study,we arrive at a conclusion that Karamaili ocean basin opened from early stage of Devonian,and began to close in late stage of Devonian,and closed at all in he Serpukhovian of late Carboniferous.And then the region became to post-collisional extension settings from late stage of early Carboniferous,with formation of bimodal volcanic rocks and igneous activity of granite.