【摘要】 富铌玄武岩是一类具有特殊地球化学特征的岛弧玄武岩。与正常岛弧玄武岩相比,它具有硅饱和并富钠的特征;同时具有相对高的Nb(一般>7×10-6)、TiO2(1%~2%)和P含量,以及低的LILE/HFSE和HREE/HFSE比值,并富集高场强元素;它的原始地幔标准化微量元素图显示了弱的Nb、Ta负异常(有时出现弱的正异常),原始地幔标准化La/Nb比值小于2(但很少小于0.7),它是由受埃达克质熔体交代过的地幔橄榄岩部分熔融形成的。由于富铌玄武岩与埃达克岩是大洋板片俯冲作用的直接产物,因此,通过对该岩石组合及与俯冲作用有关的流体和熔体的研究,不仅可以查明洋壳俯冲作用过程中的岩浆活动特征,还可以阐明洋壳俯冲及壳幔相互作用,具十分重要的地质意义。更多还原

【Abstract】 Nb-enriched basalt is a kind of arc basalt that has special geochemical characteristics.It is silica-saturated with high Na₂O contents and differs from the typical arc basalt by the extremely high Nb(>7×10^-6),TiO₂（1%～2%） and P contents with HFSE enrichment.In the primitive mantle-normalized trace element spider diagram,Nb-enriched basalts show weakly negative（sometime positive） Nb,Ta anomalies.The primitive mantle-normalized La/Nb ratios of the Nb-enriched basalts are smaller than 2（but smaller than 0.7,occasionally）.It is derived from the partial melting of mantle peridotite metasomatized by slab melts.Since Nb-enriched basalts and adakites are the direct products of subducted oceanic slab,the characteristics of magma activity and interaction between slab melts and mantle wedge can be demonstrated by the studies of this association and the nature of the relative fluids and melts.更多还原