新疆阿舍勒盆地阿舍勒组火山岩锆石U-Pb测年及地球化学特征

Zircon U-Pb Dating and Geological Significance of the Volcanic Rocks from Ashele Formation in South Altai

新疆阿舍勒盆地中阿舍勒组火山岩主要为英安质、流纹质火山角砾岩,凝灰岩、沉凝灰岩等火山角砾岩及火山熔岩,顶部为玄武岩及碧玉岩、灰岩。玄武岩亏损Nb,Ta,Ti等高场强元素,富集Ba,Th,U,Sr等大离子亲石元素,具岛弧玄武岩特征;英安岩为钙碱性系列,富集Rb,Ba,Th,U等大离子亲石元素,Nb,P,Ti亏损十分明显,具火山弧英安岩特征。玄武岩和英安岩中分别获得(387±2.8)Ma和(398.1±6.9)Ma的锆石U-Pb年龄。Hf同位素研究表明,玄武岩、英安岩物质主要来自亏损地幔,受部分熔融地壳的混染。地球化学特征显示,早中泥盆世阿舍勒组火山岩形成于俯冲构造环境。

The volcanic rocks of the Ashele Formation in The Ashele Basin of Xinjiang are mainly dacite,rhyolitic volcanic breccia,tuff,sedimentary tuff and other volcanic breccia and lava,and the top is basalt,jasper and limestone.Basalts are deficient in high-field elements such as Nb,Ta and Ti,and enrich large ion lithiasis elements such as Ba,Th,U and Sr,which are characterized by island arc basalts.Dacites are calc-alkaline series and enrich Rb,Ba,Th,U and other large ionophile elements.The Nb,P and Ti losses are very obvious and have the characteristics of volcanic arc dacite.Zircon U-Pb ages of(387.2±1.6)Ma and(398.1±6.9)Ma were obtained from basalt and dacite,respectively.Hf isotope studies show that the basalt and dacite materials mainly come from the mantle deficit and are mixed by part of the molten crust.Geochemical characteristics show that the Ashele formation volcanic rocks were formed in the subduction tectonic environment in the early and middle Devonian.