Rare and unusual mineral inclusions in diamonds from Mwadui, Tanzania (vol 132, pg 34, 1998)
Rare and unusual mineral inclusions in diamonds from Mwadui, Tanzania (vol 132, pg 34, 1998)
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产自坦桑尼亚姆瓦杜伊的钻石中稀有和不寻常的矿物内含物（第 132 卷，第 34 页，1998 年）
DOI：
10.1007/s004100050424
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发表时间：
1998
影响因子：
3.5
通讯作者：
G. Brey
中科院分区：
文献类型：
--
作者：
T. Stachel;JW Harris;G. Brey
从姆瓦杜伊金伯利岩的同生金刚石包裹体显示，一个异常肥沃的岩石圈地幔下的中非克拉通采样部分。这表现在橄榄石和斜方辉石中二辉橄榄岩与方辉橄榄岩石榴石包裹体的比例很高（1：2），Mg/Fe比值很低。应用于橄榄岩包裹体的地质测温表明非接触包裹体对之间的不平衡是常见的。石榴石-橄榄石和石榴石-斜方辉石对之间的不平衡表明在金刚石形成过程中连续的铁富集，例如导致在同一金刚石中存在方辉橄榄岩石榴石和二辉橄榄岩橄榄石。除了占主导地位的橄榄岩包体套件（88%），罕见的榴辉岩包体发生（2%）和一些不确定的共生。两个钻石，一个榴辉岩石榴石与适度的辉石固溶体和其他与一个单一的铁方镁石夹杂物，建议的贡献，一个小的岩石圈成分。在单个金刚石中发现Fe-FeO-Fe_3 O_4的缔合物表明金刚石的形成是在很大范围的氧条件下进行的，可能是沿着氧化还原前沿进行的。陡峭的成分梯度也可以通过方辉岩石榴石和SiO2相在同一金刚石中的联合出现来反映。或者，SiO2相的形成可能是由于橄榄岩源的极端碳酸化。其他不寻常的发现包括磁铁矿包裹体中硅酸盐相的出溶（即γ-橄榄石的原生溶液）和钛铁矿包裹体（含14.5 mol%的埃司科莱石（Cr2 O3）），后者与方辉橄榄岩共生硅酸盐包裹体一起。
Syngenetic diamond inclusions from the Mwadui kimberlite reveal that an unusually fertile section of lithospheric mantle beneath the Central African Craton was sampled. This is shown by a very high ratio of lherzolitic to harzburgitic garnet inclusions (1:2) and low Mg/Fe-ratios in olivine and orthopyroxene. Geothermometry applied to the peridotitic inclusions indicates disequilibrium between non-touching inclusion pairs to be common. Disequilibrium between garnet-olivine and garnet-orthopyroxene pairs suggests successive iron enrichment during diamond formation, e.g. leading to the presence of harzburgitic garnet and lherzolitic olivine in the same diamond. Apart from the dominant peridotitic inclusion suite (88%), rare eclogitic inclusions occur (2%) and a number of uncertain paragenesis. Two diamonds, one with eclogitic garnets with moderate pyroxene solid solution and the other with a single ferro-periclase inclusion, suggest the contribution of a small sub-lithospheric component. The finding of the association Fe-FeO-Fe3O4in one single diamond indicates diamond formation over a large range offO2conditions, possibly along redox fronts. Steep compositional gradients may also be reflected by the joint occurrence of harzburgitic garnet and a SiO2-phase in the same diamond. Alternatively the formation of the SiO2-phase may be due to extreme carbonation of the peridotitic source. Further unusual findings include the exsolution of a silicate phase from magnetite inclusions, (i.e. primary solution of γ-olivine) and an ilmenite inclusion with an eskolaite (Cr2O3) component of 14.5 mol%, the latter together with harzburgitic paragenesis silicate inclusions.