大兴安岭东沟营林站地区中生代火山岩地质地球化学特征及其成因意义

Geological and Geochemical Characteristics and Their Genetic Significance of Mesozoic Volcanic Rocks in Donggouyinglinzhan Area of the Dahinggan Mountains

东沟营林站地区位于大兴安岭火山岩带北部,区内岩浆活动强烈,发育从早古生代到中生代不同时期的中酸性火山岩。在详细野外地质调查的基础上,通过研究中生代火山岩岩石学特征及岩石化学数据,发现区内中生代火山岩主要为中酸性-酸性岩石,属于钙碱性系列,w(K2O)、w(Na2)O、w(TiO2)、w(FeOt)、w(MgO)、w(CaO)、w(Al2O3)、w(P2O5)与w(SiO2)具有较好的相关性,反映了岩浆分离结晶演化趋势;稀土元素大多具有铕负异常,配分曲线右倾,显示轻稀土元素富集、重稀土元素亏损的特征;微量元素的过渡族元素Cr、Co、Ni质量分数较低,大离子亲石元素Sr亏损,Rb富集,高场强元素Nb、P、Ti亏损。综合研究表明,其中生代火山岩岩浆来源于下地壳,同时与上地壳混染较多。其形成环境为古亚洲洋构造域向滨太平洋构造域转变的阶段,受蒙古-鄂霍茨克海造山后伸展和西太平洋板块俯冲双重作用的影响。

The Donggouyinglinzhan area is located at the northern volcanic belt of the Dahinggan Mountains,where the strong magma movement different stages of early Paleozoic to Mesozoic magmatism has formed acid volcanic rocks.A detailed geological survey in the wild,geognosy characteristics of the Mesozoic volcanic rocks and rock chemical data shows that the Mesozoic volcanic rocks in the region are mainly categorized in the acid rocks that belong to calc-alkaline series.The good correlation of K2O,Na2O,TiO2,FeOt,MgO,CaO,Al2O3,P2O5 and SiO2 reflects the evolution trend of fractional crystallization of magma.While the negative Eu anomalies and right-wing distribution curve owned by most REE demonstrate the characteristics of LREE enrichment and HREE loss.On the other hand,REE contains a small amount of Cr,Co and Ni which are in the transition group elements of the trace elements and are large-ion lithophile elements.However,Sr-lost and Rb-rich,HFSE Nb,P,and Ti are lost in most volcanic rocks.Comprehensive studies have shown that magma of volcanic rocks in this area must have come from the lower crust,mixed much with the upper crust.The rocks are formed in an environment of the paleo-Asian Ocean tectonic domain transforming to the peri-Pacific tectonic domain,subject to dual effects of Mongolia-Okhotsk orogenic extension and the western Pacific plate subduction.