西藏萨嘎二叠纪OIB型火山岩岩石地球化学特征及成因分析  

Geochemical Characteristics and Genesis of Permian OIB-type Volcanic Rocks in Saga Region,Tibet

作　　者：马涛[1] 张健[2] 王晓青 黄登鹏 李进喜[1] 李斌[2] 刘渭 

机构地区：[1]甘肃省地矿局第三地质矿产勘查院,甘肃兰州730050 [2]长安大学地球科学与资源学院,陕西西安710054 [3]山西省地质勘查局二一四地质队,山西运城044000 [4]中陕核工业集团地质调查院有限公司,陕西西安710100

出　　处：《西北地质》2017年第3期22-35,共14页Northwestern Geology

基　　金：基金项目:中国地质调查局"西藏1:5万冷布岗日地区4幅区域地质矿产调查"(1212011221058)

摘　　要：西藏萨嘎二叠纪火山岩主要岩石类型为强蚀变玄武岩和蚀变气孔-杏仁状安山岩。岩石学、岩石化学、岩石地球化学特征表明:曲嘎组火山岩高Ti(玄武岩、安山岩平均分别为3.16、2.15),高FeOT(平均分别为12.21、9.45),低Mg(平均分别为4.33、4.72),岩石化学特征表明其属于碱性岩系列。玄武岩、安山岩ΣREE分别为210×10^(-6)~444.7×10^(-6)、94×10^(-6)~386.1×10^(-6),LREE/HREE分别为1.77~12.18、4.02~24.4,La_N/Yb_N分别为1.14~29.66、4.19~57.16。稀土元素配分曲线呈明显右倾型,微量元素蛛网图呈"隆起"型,具碱性玄武岩和洋岛玄武岩(OIB)特征。构造环境判别图解亦指示其为洋岛玄武岩(OIB),是地幔热柱或热点物质分异的结果,没有经历地壳混染,与此带中其余二叠系火山岩均起源于二叠系新特提斯裂谷作用,证实特提斯喜马拉雅从中二叠世之前就已经开始伸展裂陷。The main types of Permian volcanic rocks are strongly altered basalt and altered stomatal-amygdaloid andesite. The study on petrology, lithochemistry, and geochemistryshows that these volcanic rocks have high Ti（basalt and andesite average in 3.16 and 2.15, respectively）, FeOT（average in 12.21and 9.45, respectively） and low Mg （with the average values of 4.33 and 4.72, respectively） contents, which belong to alkaline series.The ΣREE, LREE/HREE and LaN/YbN of basalts are 210×10-6~444.7×10-6, 1.77~12.18 and 1.14~29.66, while the ones of andesites are 94×10-6~386.1×10-6, 4.02~24.4 and 4.19~57.16, respectively. The REE distribution curve shows a dipped-right pattern, while the trace element spidergram shows ＂uplift＂ type, with thecharacteristics of alkaline basalt and OIB. The tectonic environment discriminant diagram also indicates that these rocks belong to the oceanic island basalt （OIB）, which areserved as the products of mantle plume or hotspot material differentiation,without any crustal contamination. The volcanic rocks are derived from the same source of Permian Tethys rift as the other Permian volcanics in this belt, testifying that the Tethys Himalaya began to rift before Permian.

关 键 词：OIB型火山岩 地幔柱热点 雅鲁藏布江缝合带 曲嘎组 

分 类 号：P588.145[天文地球—岩石学]