大兴安岭中段白音高老组火山岩的形成时代及地球化学特征

Formation age and geochemical characteristics of volcanic rocks from Baiyingaolao Formation of middle Da Hinggan mountains

大兴安岭中段柴河地区白音高老组火山岩主要由流纹岩及流纹质火山碎屑岩等一套酸性火山岩组成。锆石SHIRMP U--Pb定年结果显示白音高老组火山岩的年龄为131±1 Ma,为早白垩世。地球化学测试结果显示,白音高老组火山岩属钙碱性系列,其微量元素亏损Ba、Sr、P、Ti、U元素,相对富集Rb、Th、K、Nd、Hf等元素。稀土元素配分曲线右倾,轻重稀土分馏明显,具有明显的Eu负异常。研究表明,白音高老组火山岩来源于下地壳的部分熔融,其形成的构造背景可能为蒙古—鄂霍茨克洋闭合—碰撞造山后的伸展。

The volcanic rocks from Baiyingaolao Formation of Chaihe area in Da Hinggan mountains are composed of rhyolite and volcanic clastic,which is a set of felsic volcanic rocks. SHIRMP U--Pb dating shows that the age of the volcanic rocks of Baiyingaolao Formation is about 131 ± 1 Ma,belonging to the Early Cretaceous. The geochemical data show that the volcanic rocks belong to calc-alkaline series,the trace elements are characterized evidently by depletion of Ba,Sr,P,Ti,U,and enrichment of Rb,Th,K,Nd,Hf. The REE distribution curves are to the right. LREE and HREE fraction and Eu negative anomaly are both obvious. Above characteristics indicate that the volcanic rocks are likely from lower crustal melting. Tectonic setting of its formation may be the Mongolia--Okhotsk Ocean closure-stretch after collision orogeny.