【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 ,由于与俯冲作用有关的玄武岩浆底侵作用导致镁铁质下地壳发生部分熔融所致更多还原

【Abstract】 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.更多还原