东昆仑达达肯乌拉山铅锌矿床牦牛山组火山岩地球化学特征及意义

通过对达达肯乌拉山铅锌多金属矿床的牦牛山组火山岩的岩石学、岩石地球化学及年代学研究,显示牦牛山组火山岩岩相学为安山岩、凝灰岩、英安岩和流纹岩,化学成分显示其为粗面英安岩、英安岩和流纹岩。岩石地球化学研究表明,牦牛山组火山岩属高钾钙碱性系列,所有样品的稀土配分曲线具有相似的特征,稀土丰度总量REE为67.72×10-6~371.9×10-6,轻重稀土分馏明显,(La/Yb)N=3.7~26.5,δEu为0.73~1.16,微量元素以富集Rb、Ba、Th,亏损Ta、Nb为特征。锆石LA-ICP-MS U-Pb年代学研究结果显示,牦牛山组英安岩形成于(369.2±3.3) Ma,属于晚泥盆世。综合研究认为,达达肯乌拉山铅锌矿区牦牛山组火山岩具岛弧火山岩特征,产于造山后碰撞环境。

Geochemical Characteristics of the Volcanic Rocks from the Maoniushan Formation in the Dadakenwulashan Pb-Zn Deposit,East Kunlun and Its Significance

The petrology, rock geochemical characteristics and chronology ofthe volcanic rocks from the Maoniushan Formation in the Dadakenwulashan Pb-Zn deposit have been studied in this paper. The petrographic characteristics show that these volcanic rocks mainly consist of andesite, tuff, dacite and rhyolite. And theirs chemical composition suggest that these volcanic rocks can be divided into trachydacite, dacite and rhyolite. Therock geochemical characteristics indicate thatthese volcanic rocks are characterized by High K calc-alkaline series. All the samples have a similar REE distribution pattern, with total REE values ranging from 67.72×10-6 to 371.9×10-6, and obvious fractionation of light and heavy rare earth. Their(La/Yb)Nvalues are 3.7~26.5 and δEu values are 0.73~1.16.These volcanic rocks also are rich in Rb, Ba and Th elements, showing strong depletion of Ta and Nb elements.LA-ICP-MS zircon U-Pb dating shows that the age of dacite in Maoniushan Formation is (369.2±3.3) Ma, which belongs to Late Devonian. Thus, it's considered that the volcanic rocks in Maoniushan Formation have the characterstic of island-arc volcanic rocks, which formed in Post-tectonic collision environment.