吉林省白头山火山岩的微量元素及其岩石学意义

The Trace Elements of Volcanic Rocks in Baitoushan,Jilin and Their Bearing on Petrogenesis

白头山火山岩中含有一套粗面岩—钠碱流岩,与下伏的长白山玄武岩组成一个岩石系列。在白头山火山岩中,REE、Zn、Zr等元素十分富集,而过渡元素及Sr、Ba等元素极其贫 化。REE配分具明显的Eu负异常,许多不相容元素在岩石系列中表现出良好的线性关系。依据微量元素行为的数学模式对这些特征进行定性分析和定量模拟,其结果表明白头山火山岩是由长白山玄武岩岩浆经结晶分异形成的。

The volcanic rocks in the Baitoushan volcano mainly include trachyte, quartz trachyte and comendite. They, together with the underlying Changbaishan basalts, constitute a series from basalt to peralkaline acid rocks and have extreme enrichment in some imcompatible elements (REE, Zr, Nb, Zn, ect.) but are depleted in some of the others (transitional elements, St, Ba ect.). The linear correlation of some pairs of these elements has been observed in the rock series. REE distribution patterns of these rocks display a rightward decline curve with a distinct negative Eu anomaly and gradually rise in their levels and slopes from basalt fo peralkaline acid rocks These features clearly indicate the genetical relationship between the Baitoushan volcanic rocks and underlying basalts. According to the careful study of the features of the trace element models the authors suggest that the fractional crystallization may have played an important role in the origin and evolution of the Baitoushan volcanic rocks. The model of partial melting could not explain the extreme enrichment in some elements but strong depletion in the others in the peralkaline rocks. Mineral phases involving in every stage of the differentiation areestimated by variation of trace elements.