新疆巴里坤膨润土矿晚古生代哈尔加乌组安山岩地球化学特征及成因分析

Geochemical Characteristics and Genetic Analysis of Andesite from the Late Paleozoic Haerjiawu Formation in the Bentonite Mine

本文对新疆巴里坤县膨润土矿区的哈尔加乌组安山岩进行了岩石化学、稀土元素及微量元素特征等研究以期认识新疆巴里坤县膨润土矿区晚古生代安山岩的岩浆来源、演化及其成因构造环境。结果显示,哈尔加乌组安山岩属于中基性钙碱性系列岩石,贫Fe、富Na,钙质相对较贫。富Sr、Rb、Ba、Zr、Th及Hf等,亏损相容元素Ta、Ti及Nb,轻、重稀土分馏明显,无Eu异常。分析其形成的构造背景可能为俯冲消减环境,是在消减带活动大陆边缘,洋壳发生俯冲,伴随洋壳及陆壳物质混染且可能未发生过结晶分异作用。总体上为大陆一侧的活动陆缘(或大陆弧)环境,具有由岛弧向大陆过渡的迹象。

This paper analyzed the geochemical characteristics, including petrochemistry, REE and trace elements, of the Haerjiawu Formation andesite in the bentonite mine, Barkol County, Xinjiang, trying to understand magma sources, evolution, and tectonic environment of the Late Paleozoie andesite in the Barkol County bentonite mine. The results showed that the Haerjiawu Formation andesite belongs to a marie talc-alkaline rock, depleting of Fe and Ca and enriching of Na. It enriches of St, Rb, Ba, Zr, Th and Hf, depletes of compatible elements （e. g. Ta, Ti and Nb）, and has notable fractionations in both light and heavy rare earth elements, but exhibits no Eu anomaly. The tectonic studies showed that it formed in a subduction environment with active continental margin, and that it had undergone a contamination by oceanic crust material, however, no fractional crystallization evidence was found in this study. In summary, this study concluded that the forming environment of the Haerjiawu andesite is the ac- tive continental margin on the mainland （or mainland arc） side, with transition signs of from the island arc to main- land.