秦皇岛柳江地区辉绿岩脉特征及其成因

Characteristics and Cause of Diabase Dikes in Liujiang Area of Qinhuangdao

秦皇岛柳江地区辉绿岩脉主要分布于碳酸盐岩出露区的亮甲山、石门寨、潮水峪西北、砂锅店东北、揣庄北、石岭西北、鸡冠山等地,且多以脉状,岩墙、岩床等形式产出。对柳江地区辉绿岩常量元素的分析表明:w(SiO2)变化较大,且平均值较低;w(FeO+Fe2O3)平均值比基性岩类略偏高;w(Al2O3)、w(CaO)、w(MgO)、w(K2O+Na2O)的平均值均在基性岩类平均值范围内;w(TiO2)的平均值为1.53%。微量元素富集高场强元素Ta、Nb、Zr、Hf,La/Nb>1,表明岩浆上升过程中受到地壳不同程度的混染;稀土元素球粒陨石标准化分布型图各样品基本一致,呈右倾,稀土元素总量较高,轻稀土较重稀土富集,无明显的Eu异常,反映出岩浆演化过程中分离结晶作用并不明显,样品之间的稀土分馏程度相同。分析结果与研究区辉绿岩的岩相学特征相结合,表明柳江地区辉绿岩属于钾玄岩系列,来自于板内环境。结合研究区大地构造背景,认为研究区辉绿岩脉是钾玄质系列玄武质岩浆沿早期断裂或岩层层面灌入冷凝而形成。

Diabase dikes in Liujiang of Qinhuangdao mainly distribute along the limerock outcropping zone,such as Mount Liangjia,Shimen Village,Chaoshuiyu（northwest）,Shaguodian（northeast）,Chuaizhuang Village（north）,Shiling Ridge（northwest）,Mount Jiguan and other regions as veins,dykes,sills,and other output forms.The constant element analysis of diabase in Liujiang indicates that the content of SiO2 varies greatly with a fairly low average.The average content of FeO＋Fe2O3is higher than the average of basic rocks;the average values of Al2O3,CaO,MgO and K2O＋Na2O are within the average of basic rocks;the average value of TiO2 is 1.53%;the enrichment of HFSE Ta,Nb,Zr,Hf,La/Nb value is higher than 1;it shows that magma was contaminated by the crust material in different degree during its ascending.The total REE is high,and LREE are more than HREE.Thechondrite normalized REE distribution patterns are consistent,tilted to the right,with no obvious Eu anomaly.This reflects that the fractional crystallization is not obvious in magma,and evolution and REE fractionation degree between samples is the same.The petrographic features of the diabase in Liujiang indicate that the diabase in Liujiang was derived from shoshonitic series in the intra-plate rift environment.According to the tectonic setting of the study area,the author concludes that shoshonitic series basaltic magma moved along the fractures,cooled down,then formed the diabase.