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针对西藏则学结仁-朗日火山岩的野外地质、岩石学、锆石U-Pb定年以及岩石地球化学等方面的系统研究,结果表明:结仁-朗日火山岩为一套中酸性的火山熔岩及碎屑岩,火山作用以爆发作用为主,岩石类型主要为粗面岩、英安岩及流纹质晶屑岩屑凝灰岩。其LA-ICP-MS锆石U-Pb年龄为50.2Ma±2.2Ma~56.18Ma±0.60Ma,并非前人厘定的嘎扎村组(N2g)火山岩,而属林子宗群年波组(E2n)火山岩。结仁-朗日火山岩具有高K(K2O质量分数为2.68%~4.09%)低Ti(TiO2质量分数为0.69%~0.85%)、高钾钙碱性-钾玄岩系列的主量元素岩石地球化学特征;其稀土配分模式呈轻稀土富集的右倾曲线,LaN/YbN比值为9.13~14.29,普遍出现负铕异常(δEu=0.35~0.84);微量元素方面表现为Nb,P,Ti的亏损;结仁-朗日火山岩具有高放射成因Pb的同位素组成特征。总体上,结仁-朗日火山岩形成于雅鲁藏布洋壳向北俯冲到印度板块与欧亚大陆碰撞的过渡环境,岩浆起源于楔形地幔部分熔融所形成的基性岩浆在上升过程中混染陆壳熔融所形成的酸性岩浆。
A systematic study on the geology, petrology, zircon U-Pb dating and geochemistry of the Langxian volcanic rocks shows that the Jieren-Longyan volcanic rock is a medium-acidic volcanic lava And clastic rocks. The volcanism is dominated by the eruption. The types of rocks are mainly rough rock, dacite and rhyolite clastic tuff. The zircon U-Pb ages of LA-ICP-MS are 50.2Ma ± 2.2Ma ~ 56.18Ma ± 0.60Ma, which is not the predecessor of the Ngg volcanic rocks, Volcanic rocks. The Jungren-Langri volcanic rock has the main elements of high-K (K2O mass fraction of 2.68% ~ 4.09%) and low Ti (TiO2 mass fraction of 0.69% ~ 0.85% The LaN / YbN ratio is 9.13-14.29. The negative Eu anomaly (δEu = 0.35-0.84) generally appears. The trace elements show the loss of Nb, P and Ti ; The Jiren-Longi volcanic rocks have the isotopic composition of high-radiogenic Pb. In general, the Jungren-Langri volcanic rocks formed in the transitional subduction of the Brahmaputra oceanic crust to the collision between the Indian plate and the Eurasian continent. The magma originated from the mafic magmas formed by the partial melting of the wedge-shaped mantle during the uplifting Acidic magma formed by the melting of the continental crust.