摘要
峨眉山大火成岩省二滩地区玄武岩W（SiO2）／％=40．5～59．65；普遍高碱，w（K2O＋Na2O）：2．64％～7．67％。W（TiO2）：2．10％～6．53％，Ti／Y〉500，该区玄武岩属于高钛（HT）型玄武岩；其Mg^#：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Eu^3＋／Eu^2＋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，Ni，Zr，TiO2和Mg^#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（Rb，Ba，Th，U，Nb，Ta，La，Ce等）配分曲线与OIB相似，及其Ta／Yb vs Th／Yb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，Ba／Th，Zr／Nb，La／Nb，Ba／Nb等比值介于EMI OIB和EMII OIB之间，以及Ce／Pb比值也说明：二滩玄武岩缺少HIMU OIB端元组分，是EMI OIB和EMII OIB两端元的混合产物。
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（31 -53）. 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 Eu^3＋/Eu^2＋ 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 Data of Sr-Nd-Pb isotope（unpublished） and Ce/Pb ratio indicate that the source of Ertan basalts is the mixture of EMI OIB end member and EMII OIB end member without HIMU OIB end member.
出处
《矿物岩石》
CAS
CSCD
北大核心
2006年第3期77-84,共8页
Mineralogy and Petrology
基金
国家自然科学基金(批准号:40372048
40573036)
