青海喀雅克登塔格晚三叠世鄂拉山组火山熔岩地球化学特征及构造环境探析

Analysis of the geological features and tectonic setting of volcanic lava in Elashan group,Qinghai rovince

通过对喀雅克登塔格晚三叠世鄂拉山组火山熔岩进行化学分析和微量元素分析,发现岩石以富Si、Na,高K,贫Ti、Ca、Mg、Fe为特征,在SiO2-Na2O+K2O图解中几乎全部样品均落在亚碱性系列区,在AFM图解中所有样品均落在钙碱性系列区,为高钾钙碱性系列;微量元素以低Cr,Co,高Ba,且K、Rb、Ba和Th较强的富集,Sr、Ti、Sc、Cr明显亏损为特征;稀土元素分析表明为轻稀土富集型,且铕具有明显的负异常特征。经δEu-Sr值图解和Logσ-Logτ图解分析后,认为区内熔岩可能形成于以侧向挤压为主的陆—陆后碰撞环境,为碰撞过程中加厚地壳物质发生部分熔融后的产物。

By chemical analysis and trace element analysis of volcanic lava of Elashan group in Kayakedengtage,the results reveal that the ore is characterized by rich Si and Na,high K,poor Ti and Ca,etc.In the SiO2-Na2O＋K2O diagram,almost all samples fall into the sub-alkaline series area.In the AFM diagram,all the samples fall in the calc-alkaline series area too.So the volcanic lava belong to high-K calc-alkaline rock series.At the same time,the trace elements reveal low Cr and Co,high Ba,rich K and Rb,etc.Sr,Ti,Sc,Cr characterized by significant loss;REE analysis shows that it belong to LREE-enriched and Eu negative anomaly.After diagram analysis of δEu-Sr and Logσ-Logτ,the volcanic lava may be formed during the tectonic setting of post-collision between blocks.It＇s the products of crust thickening and partial melting.