Mineralogy and texture of Fe-Ni sulfides in CI1 chondrites: Clues to the extent of aqueous alteration on the CI1 parent body
Mineralogy and texture of Fe-Ni sulfides in CI1 chondrites: Clues to the extent of aqueous alteration on the CI1 parent body
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DOI：
10.1016/j.gca.2005.01.003
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发表时间：
2005-05-15
影响因子：
5
通讯作者：
Russell, SS
中科院分区：
文献类型：
--
作者：
Bullock, ES;Gounelle, M;Russell, SS
为了更好地了解水蚀变对 CI1 母体的作用，我们分析了 5 种已知 CI1 球粒陨石中的 4 种中铁镍硫化物的结构、成分和矿物组合。 CI1 球粒陨石中最常见的硫化物是缺铁的 Fe,Ni 硫化物磁黄铁矿 ([Fe,Ni](1-x)S)，其成分与化学计量的硫铁矿 (FeS) 接近。其中三个 CI1（Alais、Ivuna 和 Tonk）也含有镍黄铁矿 ([Fe,Ni](9)S-8,)，尽管镍黄铁矿在 Ivuna 中是罕见的相。本研究中在 Alais 和 Ivuna 中都发现了Cubanite (CuFe2,S-3)，尽管在 Orgueil 中也有报道（MacDougall 和 Kerridge，1977）。所有四种球粒陨石中的磁黄铁矿颗粒均形成六边形、矩形或不规则形状，并且没有显示出镍或钴分带的证据。与阿莱或唐克相比，奥尔盖尔和伊武纳的磁黄铁矿颗粒通常更小，并且显示出更多的“腐蚀”或“凹坑”。我们认为 CI1 球粒陨石中存在的前体硫化物是陨铁矿，在 100 摄氏度或更低的温度下在母体上发生角砾化和氧化过程中，将硫铁矿转化为磁铁矿和磁黄铁矿镍黄铁矿包裹体。随后，对母体的持续改造去除了镍黄铁矿——部分来自阿莱、唐克和伊武纳，完全来自奥盖尔——留下磁黄铁矿，并在镍黄铁矿原来所在的位置留下了空间（“腐蚀”）。来自镍黄铁矿的 Ni 被掺入水铁矿中，在水铁矿的表面形成 Ni,Na 硫酸盐 Ni-bloedite。根据磁黄铁矿晶粒内的尺寸和丰富的“腐蚀”，结合其他作者的观察，我们得出结论，Orgueil 和 Ivuna 比 Alais 和 Tonk 经历了更大程度的蚀变。需要进一步的工作来评估镍黄铁矿比磁黄铁矿优先溶解的条件，因为陆地文献的研究表明后者矿物被优先去除。版权所有 (c) 2005 爱思唯尔有限公司
To better understand the role of aqueous alteration on the CI1 parent body, we have analyzed the texture, composition and mineral associations of iron nickel sulfides in four of the five known CI1 chondrites.The most commonly-occurring sulfide present in the CI1 chondrites is the iron-deficient Fe,Ni sulfide pyrrhotite ([Fe,Ni](1-x)S), that has a composition close to that of stoichiometric troilite (FeS). Three of the CI1s (Alais, Ivuna and Tonk) also contain pentlandite ([Fe,Ni](9)S-8,), although pentlandite is a rare phase in Ivuna. Cubanite (CuFe2,S-3) was found in both Alais and Ivuna in this study, although it has also been reported in Orgueil (MacDougall and Kerridge,1977). The pyrrhotite grains in all four chondrites form hexagonal, rectangular or irregular shapes, and show no evidence of Ni or Co zoning. The pyrrhotite grains in Orgueil and Ivuna are, in general, smaller, and show more "corrosions," or "embayments," than those in Alais or Tonk.We suggest that the precursor sulfide present in the CI1 chondrites was troilite which, during brecciation and oxidation on the parent body at a temperature of 100 degrees C or less, converted the troilite to magnetite and pyrrhotite with pentlandite inclusions. Subsequently, continued alteration on the parent body removed pentlandite-partially ally from Alais, Tonk and Ivuna, completely from Orgueil-leaving behind pyrrhotite with spaces ("corrosions ") where the pentlandite had been. Ni derived from the pentlandite was incorporated into ferrihydrite, onto the surface of which the Ni,Na sulfate Ni-bloedite formed.Based on the size and abundant "corrosions" within pyrrhotite grains, combined with observations from other authors, we conclude that Orgueil and Ivuna have undergone a greater degree of alteration than Alais and Tonk. Further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite, as the study of terrestrial literature indicates that the latter mineral is preferentially removed. Copyright (c) 2005 Elsevier Ltd.