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    羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩地球化学特征及其构造意义

    Geochemical characteristics and tectonic significance of Qixianian volcanic rocks in Zhigengaka area, Zhiduo County, eastern Qiangtang

    • 摘要: 提要:羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩主要由中基性火山碎屑岩及熔岩组成,火山岩地球化学研究表明,其主元素表现为高TiO2和低TiO2两种特征,球粒陨石标准化稀土配分模式为LREE富集型,MORB标准化的微量元素配分型式为大洋隆起型,显示岩浆形成于板内裂谷构造环境。Sr、Nd、Pb同位素地球化学研究表明火山岩显示明显的亏损地幔源区特征。综合研究表明直根尕卡一带二叠纪栖霞期火山岩形成于大陆边缘拉张构造(或陆缘始裂谷)环境,岩浆起源于地幔,属地幔柱作用的产物。

       

      Abstract: Abstract:Qixianian volcanic rocks in Zhigengaka area consist of pyroclastic rocks and lava. Geochemical researches on major elements, trace elements and Sr, Nd, Pb isotopes suggest that these volcanic rocks originated from the mantle in an extension or fresh rift basin environment on the continental margin and were induced by mantle plume upwelling. On the basis of major elements, the volcanic rocks can be divided into two types characterized respectively by high TiO2 and low TiO2. Chondrite normalized REE patterns show light REE enrichment, with MORB normalized trace elements like the pig back, indicating that these volcanic rocks were formed in an intra-continental rift environment. Sr, Nd, Pb isotopic geochemistry suggests that they were derived from a depleted mantle source.

       

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