Carbonate-Carbonate Immiscibility, Neighborite and Potassium Iron Sulphide in Oldoinyo Lengai Natrocarbonatite
Carbonate-Carbonate Immiscibility, Neighborite and Potassium Iron Sulphide in Oldoinyo Lengai Natrocarbonatite
复制标题
Oldoinyo Lengai 钠碳酸盐中的碳酸盐-碳酸盐不混溶性、邻石和硫化铁钾
作者：
R. Mitchell
摘要1995年10月17日和1995年12月15-19日从Oldoinyo Lengai火山（坦桑尼亚）喷发的斑状碳酸钠岩熔岩与以前研究的熔岩不同，因为它们保留了指示基质碳酸盐-碳酸盐不相容性的纹理。不混溶部分被认为包括：富含Na-K-Ca-CO2-Cl的含F流体，结晶钙铝榴石、钠钾石盐、钾邻长岩以及复杂的富钡碳酸盐;和富含Na、贫Cl的碳酸盐液体，接近Nyeretite-钙铝榴石共晶组合物。给出了钾钠长石的成分数据，这种矿物是第一个公认的发生在岩浆环境中的氟基钙钛矿族矿物。新的组成数据也给出了以前公认的钾铁硫化物，这表明，这一阶段可能是一个固溶体之间的三元硫化物，KFe 3S 4，K2 Fe 3S 4，和KFe 2S 3。纹理和共生数据的解释表明，这些最近的熔岩比以前调查的Oldoinyo Lengai熔岩和natrocarbonate是一个高度进化，而不是原始的岩浆。
Abstract Porphyritic natrocarbonatite lavas erupted from the Oldoinyo Lengai volcano (Tanzania) on 17 October 1995 and 15-19 December 1995 differ from previously studied lavas in that they preserve textures indicative of groundmass carbonate-carbonate immiscibility. The immiscible fractions are considered to involve: a Na-K-Ca-CO2-Cl-rich, F-bearing fluid crystallizing gregoryite, sodian sylvite, potassium neighborite as well as a complex Ba-rich carbonate; and a Na-rich, Cl-poor carbonate liquid approximating to a nyerereite-gregoryite cotectic composition. Compositional data are given for potassium neighborite, this mineral being the first recognized occurrence of a fluorine-based perovskite group mineral in a magmatic environment. New compositional data are also given for a previously recognized potassium iron sulphide which indicate that this phase is probably a solid solution between the ternary sulphides, KFe3S4, K2Fe3S4, and KFe2S3. Textural and paragenetic data are interpreted to suggest that these recent lavas are more evolved than previously investigated Oldoinyo Lengai lavas and that natrocarbonatite is a highly evolved rather than a primitive magma.