【摘要】 峨眉山大火成岩省二滩地区玄武岩w(S iO2)/%=40.5~59.65;普遍高碱,w(K2O+N a2O)=2.64%~7.67%。w(T iO2)=2.10%~6.53%,T i/Y>500,该区玄武岩属于高钛(HT)型玄武岩;其M g#=58~84,明显高于高于宾川高钛玄武岩(31~53),说明岩浆演化程度明显低于宾川高钛玄武岩浆。岩石样品中Sr显示明显负异常,暗示了二滩玄武岩经历了广泛的斜长石结晶分离;而Eu不显异常,则反映了玄武岩岩浆中有高Eu3+/Eu2+比值的存在,其环境为氧化环境。在二滩玄武岩和宾川高钛玄武岩中,N i,Z r,T iO2和M g#均显示了明显差异,说明二滩玄武岩具有独立的地球化学特征。二滩玄武岩不相容元素(R b,B a,Th,U,N b,T a,L a,C e等)配分曲线与O IB相似,及其T a/Y b vs Th/Y b双变量图解也显示出了富集地幔特征,这些特征反映了峨眉山二滩玄武岩源区为富集地幔源,玄武岩岩浆可能为地幔柱物质。此外,B a/Th,Z r/N b,L a/N b,B a/N b等比值介于EM I O IB和EM II O IB之间,以及C e/Pb比值也说明:二滩玄武岩缺少H IMU O IB端元组分,是EM I O IB和EM II O IB两端元的混合产物。更多还原

【Abstract】 New trace and major-element data are presented for Emeishan flood basalts from Ertan area,southwestern China.The content of w（SiO₂） is 40.5% to 59.65% for Ertan basalts,most of the rocks are alkalic,w（K₂O+Na₂O）=2.64% to 7.67%.w（TiO₂）=2.10% to 6.53%,Ti/Y>500,thus Ertan basalts are high-TiO₂（HT） type lavas.Ertan basalts have high Mg^#（58～84）,which is higher than those of Binchuan basalts（31⁵3）.The samples from Ertan area display significant negative Sr anomaly,which imply these rocks have undergone extensive fractionation of plagioclase evidenced by the presence of large proportion plagioclase phenocrysts in samples.The lack of negative Eu anomaly in samples probably reflects a high Eu³⁺/Eu²⁺ ratio and oxidizing environment in the magma.Negative Zr anomaly is a notable feature for Ertan basalts,which may be related to different evolution of magmas.Content of TiO₂,Ni,Zr for Ertan basalts is different from that of Binchuan basalts respectively,suggesting that Ertan basalts possess special geochemical signature.The plot of Ta/Yb Vs.Th/Yb for Ertan basalts displays the characteristics of enriched mantle（EM） and the pattern of incompatible trace-element is OIB-like,so Ertan basalts are plume-derived.In addition,the ratios of Nb/Ta,Ba/Th,Zr/Nb,La/Nb,Ba/Nb are between EMI OIB and EMII OIB.Data of Sr-Nd-Pb isotope（unpublished） and Ce/Pb ratio indicate that the source of Ertan basalts is the mixture of EMI OIB end member and EMII OIB end member without HIMU OIB end member.更多还原