The late carboniferous rhyolites with columnar joints have been found in the West Junggar,then we studyed their tectonic environment through the geochemical characteristics.The rhyolites from the West Junggar have the characteristics of high K,low Na,so they belong to high-k calc-alkaline or cala-alkaline magmatic series.According to the V patterns of the REE distribution patterns of the rhyolites,Eu is deficited,testifying the process of the crystallization differentiation of plagioclase.The rhyolites are enrichment of elements Rb、K (LILE),and deficient of Nb、Ta (HFSE),this is same to the characteristic of subduction zone magma.The study shows that the rhyolites which belong to A2 rock type derived from post-orogenic tectonic environment.The rhyolites and granites batholith have the same magmatic source and both belong to rich alkaline magmatism in orogenic environment.Similarly to the environment of the rhyolites in the east China,the study proves the existence of sealand transition zone during the late Paleozoic,indicating that the Junggar Oceanic Plate subducted under the Kazakhstan Plate.Ocean subduction mainly developed in Karamay-Baogutu area,where the Junggar oceanic plates subducted to the northwest under the Kazakhstan plates.The rich alkaline magmatism in the post-orogenic stretch environment which the late carboniferous rhyolites with columnar joins occured,put an end to the ocean-land transition environment.%本文在中亚造山带西部的西准噶尔地区新发现晚石炭世柱状节理流纹岩,并根据其地球化学特征探讨了其形成的构造环境.岩石化学分析的结果表明,柱状节理流纹岩的主量元素具有高钾低钠的特征,属于高钾钙碱性和钙碱性岩浆系列;球粒陨石标准化稀土元素分配模式表现为V字型,Eu亏损,说明发生了斜长石的结晶分异.大离子亲石元素(LILE) Rb、K相对富集,高场强元素(HFSE) Nb、Ta出现负异常,反映了俯冲带岩浆的特征.研究表明该流纹岩属于A2型,形成于后造山的伸展构造环境;与该地区晚石炭世大型花岗岩类岩基具有同源性,同属于后造山伸展环境下的富碱岩浆作用.对比我国东部沿海中生代柱状节理流纹岩的大陆边缘构造环境,本研究认为西准噶尔地区在晚石炭世存在由大洋俯冲向陆内环境转变的洋陆转换特征;之前的大洋俯冲主要发育在克拉玛依-包古图一带,具有准噶尔洋板块向西北方向在哈萨克斯坦微陆块之下俯冲的构造极性.正是由晚石炭世柱状节理流纹岩所代表的后造山伸展环境下的富碱岩浆作用,终结了该地区洋陆过渡带环境.
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