甘肃白银厂矿田流纹岩的成因及其构造意义  

Tectonic significance and origin of the rhyolites from Baiyin Mining Field in Gansu Province

作　　者：王金荣[1] 郭原生[1] 董宁芳[1] 李双文[1] 翟新伟[1] 孟桂生[2] 杨永钧 

机构地区：[1]兰州大学资源环境学院,甘肃兰州730000 [2]白银有色公司金属小铁山矿,甘肃白银730900

出　　处：《兰州大学学报（自然科学版）》2003年第4期88-92,共5页Journal of Lanzhou University(Natural Sciences)

基　　金：甘肃省自然科学基金资助项目 ( ZS0 0 1 -A2 5 -0 0 6-Z)

摘　　要：白银厂矿田早—中寒武世流纹岩被认为是大陆裂谷环境或洋内弧岩浆作用的产物 .地球化学分析结果显示 :流纹岩具有 Ti,Nb,Ta明显负异常 ,Sr和 P中等负异常 ,LREE略富集到富集 ,相对亏损 HFSE,La/ Nb值为 1～ 2 ,La/ Th值为 1 .1～ 2 .5 ,Th/ Ta值高 ( 6～ 1 2 ) ,部分样品表现为 MREE负异常的稀土元素配分特征 ,δEu=0 .5～ 1 .1 ,( 87Sr/ 86 Sr) I=0 .70 2 6～ 0 .70 48,εNd( t) =+5 .60～ +6.1 4.综合其地球化学特征 ,推测流纹岩形成应是在大陆地壳基础上 。Early middle Cambrian rhyolites from Baiyin Mining Field were considered to have resulted from magmatism of continental rift.However,the analytical results of the geochemical properties show that the rhyolites are characterized by low Ti and obviously negative anomaly of Nb Ta,and moderate negative anomaly of Sr and P,slight depletion to obvious enrichment of LREE,relative depletion of HFSE,and La/Th = 1.1～2.5,La/Nb =1～2 and high ratios of Th/Ta (6～12),and that the rhyolites with ( 87 Sr/ 86 Sr) I =0.702 6～0.704 8,ε Nd ( t )=+5.60～+6.14,δEu=0.5～1.1 have characteristic REE distribution patterns of negative anomaly of MREE.According to the geochemistry of the volcanic rocks,it can be inferred that in normal continental margin arc,the rhyolites resulted from partial melting of the previously formed mafic lower crust by underplating of basaltic magmas relative to the plate subduction during the early middle Cambrian.

关 键 词：流纹岩 地球化学 陆缘弧 镁铁质下地壳 白银厂矿田 

分 类 号：P588[天文地球—岩石学]