新疆东天山滑石山一带贝义西组火山岩形成时代及构造环境

Age and Tectonic Setting of Volcanic Rock of the Beiyixi Formation in the Huashishan Region, East Tianshan Mt., Xinjiang

新疆东天山滑石山一带贝义西组主要为一套海相火山岩,有基性和中酸性两类,以酸性火山岩为主,火山岩相划分为爆发相和溢流相,以溢流相为主,具双峰式喷发特征。基性玄武岩为钠质碱性岩石,轻稀土富集,铈亏损,大离子亲石元素K、Rb相对富集,Sr亏损明显,高场强元素(HFSE)无明显亏损。酸性火山岩主要为高钾钙碱性岩石,轻稀土富集,铈、铕亏损,大离子亲石元素K、Rb相对富集,Sr亏损明显,高场强元素(HFSE)无明显亏损。酸性火山岩通过LA-ICP-MS锆石U-Pb获得年龄为799~808Ma。结合地质背景认为贝义西组火山岩形成于大陆裂谷环境,是Rodinia超大陆在塔里木克拉通北缘裂解产物。

The Beiyixi Formation in the Huashishan area,Eastern Tianshan Mountains,Xinjiang is mainly composed of a set of marine basic and intermediate-acid volcanic rocks in which acid volcanic rock is dominant.They may be divided into eruption and overflow phases with bimodal eruption.The overflow phase dominates over the eruption phase.The basic volcanic rock is Na-rich basalt which is characterized by enrichment in LREE,large ion lithophile elements such as K and Rb and depletion in Ce and Sr.The acid volcanic rock is K-rich calc-alkaline volcanic suite and characterized by enrichment in LREE,large ion lithophile elements such as K and Rb and depletion in Ce,Eu and Sr.Zircon U-Pb age values of the acidic volcanic rock range from 799 Ma to 808 Ma.In combination with geological background,the volcanic rock of the Beiyixi Formation can be considered as the product of continental rift resulted from Rodinia splitting.