青海省小灶火河西地区契盖苏组火山岩特征及其构造环境判别

Characteristics of Volcanic Rocks and Tectonic Setting of Qigesu Formation in West of XiaoZaohuo,Qinghai Province

分布于小灶火地区的契盖苏组火山岩为中酸性、亚碱性之钙碱性系列低钛型的火山岩;火山岩的稀土元素总量(∑REE)变化较大(82.05×10^(-6)~177.91×10^(-6)),轻稀土元素相对富集(LREE/HREE平均在6.82),稀土元素配分曲线均呈现右倾较缓的平滑线。δEu均小于1,反映出铕亏损,与岛弧火山岩相似。火山岩微量元素蛛网图与大陆壳火山岩的特征极为相似。通过构造环境分析认为,区内契盖苏组火山岩应形成于陆内造山环境,在地球化学成分上具不成熟陆缘火山弧的特征,并将其喷发时代为顶志留—早泥盆世。

According to the analysis, the volcanic rocks of Chegasu Fomlation in the Xiaozao area are medium- acidic and sub-alkaline calc-alkaline series of low-titanium volcanic rocks. The total REE content of volcanic rocks varies greatly （82.05 re 10-6 -177.91 re 10-6）, the light rare earth elements are relatively enriched （LREE/ HREE average is 6.82） , and the rare earth element distribution curves all show in a smooth line with a gentle rightward inclination. The reEu is less than reflecting the europium in loss similar to the island arc volcanic rock. The trace elements of volcanic rocks are very similar to those of continental crust volcanic rocks. According to the tectonic environment analysis, the volcanic rocks of Qiqisu Folanation in the area should be folaned in the intracontinental orogenic environment with the characteristics of the immatmre continental marginal volcanic arc in the geochemical composition. And the eruption era is the top Shiliu-Early Devonian.