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Nb,Ta的硅酸盐地球质量不平衡问题争论由来已久,备受关注。近年来研究发现,含金红石的榴辉岩Nb/Ta往往高于球粒陨石值(Nb/Ta=17.5),暗示其可能是平衡地球Nb亏损的独立储库。而洋壳玄武岩部分熔融实验表明Ta比Nb更倾向进入金红石晶格,这意味着作为俯冲洋壳部分熔融残留相的榴辉岩Nb/Ta不可能高于原岩。为了解释地质观察和实验结果之间的矛盾,系统分析了中国大陆科学钻探工程(CCSD)主孔、先导孔及附近地表榴辉岩的矿物微量元素。结果发现:榴辉岩中的Nb,Ta主要存在于金红石之中,其他矿物中含量极少;Nb,Ta之间存在着强烈分异(Nb/Ta=5.3～96.2),并总体上具有超球粒陨石的特征;韭闪石和多硅白云母的Nb/Ta平均分别为48.6,21.8,显示了很强的Nb,Ta分异能力;其他矿物如石榴石、绿辉石、绿帘石、磷灰石等的Nb、Ta含量及Nb/Ta都很低,对Nb-Ta分异不造成影响。认为导致Nb-Ta分异的不是金红石,而应出现在洋壳俯冲过程中金红石相出现之前的脱水和部分熔融阶段。富含Ti的角闪石(韭闪石)和白云母可能对Nb-Ta分异起到了决定性的作用。等金红石相出现之后,由于其对Nb,Ta的绝对控制作用,此前阶段的分异结果便被固定在金红石中而继承下来。因此,含金红石的榴辉岩常常表现出超球粒陨石Nb/Ta的特征,与金红石不能有效地分异Na,Ta的实验结果之间并不矛盾。在不均匀的上地幔中含金红石的榴辉岩是可能的超球粒陨石Nb/Ta储库之一。
The controversy over the unbalanced earth quality of silicates in Nb and Ta has drawn a great deal of attention for many years. Recent studies have found that the Nb / Ta eclogite-bearing eclogites tend to be higher than the chondrite value (Nb / Ta = 17.5), suggesting that they may be an independent reservoir that balances the Earth’s depletion of Nb. The partial melting experiments of the oceanic basalts show that Ta is more likely to enter the rutile lattice than Nb, which means that the Nb / Ta eclogites, which are partially molten residual phases of the subducted oceanic crust, can not be higher than the original rocks. In order to explain the contradiction between the geological observation and the experimental results, the trace elements in the main hole, pilot hole and surface eclogites of the China Continental Scientific Drilling Project (CCSD) were systematically analyzed. The results show that Nb and Ta in eclogite mainly exist in the rutile, while the contents of other minerals are extremely small. There is a strong difference between Nb and Ta (Nb / Ta = 5.3 ~ 96.2) Chondrite and chondrite meteorites. The average Nb / Ta ratios of all-graded amphibole and pheismite are 48.6 and 21.8, respectively, indicating strong Nb and Ta dissimilarities. Other minerals such as garnet, omphacite, epidote, The contents of Nb, Ta, and Nb / Ta in apatite and the like are very low, and do not affect the Nb-Ta differentiation. It is believed that the rutile that led to Nb-Ta differentiation is not rutile, but rather dehydration and partial melting prior to the rupture of the oceanic crust. Ti-rich amphiboles (leechesite) and muscovite may have played a decisive role in Nb-Ta differentiation. After the occurrence of the rutile phase, due to its absolute control over Nb and Ta, the result of the previous stage differentiation was inherited in the rutile. Therefore, the eclogite-bearing eclogites often exhibit the characteristics of Nb / Ta super-chondrites and are not inconsistent with the experimental results that rutile can not effectively differentiate between Na and Ta. The rutile-containing eclogite in the non-uniform upper mantle is one of the possible Nb / Ta super-chondritic reservoirs.