新疆巴里坤塔格柳树沟组玄武岩成因及其构造环境——岩石地球化学及Sr-Nd-Pb同位素证据

东天山巴里坤塔格地区分布大量的柳树沟组火山岩, 笔者以玄武岩为研究对象, 对其岩石学、岩石地球化学及同位素地球化学研究表明:巴里坤塔格柳树沟组玄武岩均属拉斑玄武岩系列, 并富集大离子亲石元素(Sr、K、Rb、Ba、Th)和轻稀土元素, 亏损高场强元素(Nb、Ta、Ti)和重稀土元素, Sr-Nd-Pb同位素显示低(87Sr/86Sr)t=0.703 82~0.706 67, 低(206Pb/204Pb)t=17.857~18.054, (207Pb/204Pb)t=15.494~15.545, (208Pb/204Pb)t=37.746~37.798、高εNd(t)=+4~+8.3的亏损地幔源区特征, 并受到了陆壳物质混染。通过与博格达东段伊齐—小红柳峡同时期玄武岩的对比, 认为巴里坤塔格地区在晚石炭世与博格达具有相同的构造属性, 同属于大陆裂谷环境, 但由于分属裂谷不同的演化阶段, 地球化学特征具有一定的差异。

Genesis and Tectonic Environment of Basalts in Balikuntage,Xinjiang:Implications from Geochemistry and Sr-Nd-Pb Isotopes

The volcanic rocks from the Liushugou formation are widely distributed in Balikuntage area, Xinjiang. Study on the basalt, their petrology, geochemistry and isotope geochemistry indicate that, the basalts in this area belong to tholeiite series and are characterized by LREE, LILE(Sr, K, Rb, Ba, Th) enrichments and HFSE(Nb, Ta, Ti), HREE depletion, low Sr-Nd-Pb isotope(87Sr/86Sr)t=0.70382-0.70667;(206Pb/204Pb)t=17.857-18.054; (207Pb/204Pb)t=15.494-15.545; (208Pb/204Pb)t=37.746-37.798 and high εNd(εNd(t)=+4-+8.3), which show its depleted mantle origin and contamination of crust materials. Through comparing with the basalts of the eastern Bogda in the same period, the results show that Balikuntage has the similar structure attributes with the Bogda area, which is the continental rifting in the late Carboniferous. But they belong to different stages of rifting evolution, thus, their geochemistry exhibits some disparities.