Study on the volcanic rocks from Elashan Formation in Zhong Juh area, Qinghai Province, indicates that it belongs to acid-intermediate high-K and low-Ti calc-alkali series. The analysis results reveal that ∑REE varies from 139.45×10-6to 219.55×10-6,with enrichment of LREEs(LREE/HREE of 7.695-13.46,averagely 9.09).The distribution patterns show gently right-dipping smooth curves with weak negative Eu anomaly(δEu=0.53-0.83). The general uniformity of trace element curve patterns reflects the homogeneity of volcanic rocks in this area. According to the analysis on tectonic environment, it is concluded that the volcanic rocks is the product of magmatic arc formed by compression and collision.%分析研究认为,中灶火地区分布的鄂拉山组火山岩为中酸性、亚碱性之钙碱性系列高钾低钛型的火山岩;火山岩的稀土元素总量变化较大(139.45×10-6~219.55×10-6),轻稀土元素相对富集(LREE/HREE在7.695~13.46之间,平均为9.09),稀土元素配分曲线均呈现右倾较缓的平滑线.δEu值在0.53~0.83之间,具有弱负Eu异常;岩石微量元素配分图中曲线型式基本一致,反映了该区火山岩的同源性.通过构造环境分析认为,区内鄂拉山组火山岩形成于挤压碰撞作用形成的岩浆弧.
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