西藏仲巴地块加达钾质火山岩LA-ICP-MS锆石U-Pb年龄和地球化学特征
LA-ICP-MS zircon U-Pb age and geochemical characteristics of Jiada potas-sic volcanic rocks in Zhongba terrane, Tibet
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摘要: 新生代青藏高原钾质火山岩发育,主要集中于藏北地区和拉萨地块内,仲巴地块中鲜见报道。对仲巴地块中发现的加达钾质火山岩进行研究,其岩石类型以粗面质为主,岩浆以溢流相-喷发相不间断喷发。样品普遍显示高钾高铝,低碱,偏酸性,富集轻稀土元素和大离子亲石元素,亏损高场强元素,具弱负Eu异常,贫Y和Yb,Sr含量较高,类似于典型的埃达克质岩的地球化学特征。粗面玄武安山岩样品LA-ICP-MS锆石U-Pb年龄为17.03±0.32Ma,形成时代为中新世。加达钾质火山岩浆来源于挤压增厚的下地壳部分熔融,其产出的构造背景是后碰撞伸展环境。Abstract: Cenozoic potassic volcanic rocks are widely distributed in the Tibetan Plateau, mainly in northern Tibet and Lhasa block with a few reports in Zhongba terrane. The study of Jiada potassic volcanic rocks found in Zhongba terrane shows that the rocks are almost exclusively trachyte, and the magma erupted incessantly by overflowing and erupting. These rocks are also characterized by high potassium and high aluminum, rich LILE, LREE and Sr, and poor HFSE,Y and Yb, with Eu negative anomaly. Their geochemi-cal characteristicss are similar to those of typical adkite rocks. The LA-ICP-MS zircon U-Pb age of trachyandesites is 17.03±0.32Ma, which means that these volcanic rocks were formed in Miocene. The Jiada potassic magma was derived from partial melting of thickened crust. The rocks represent post-collisional tectonic setting and extension environment.
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