Mineralogy of iron sulfides in CM1 and CI1 lithologies of the Kaidun breccia: Records of extreme to intense hydrothermal alteration
Mineralogy of iron sulfides in CM1 and CI1 lithologies of the Kaidun breccia: Records of extreme to intense hydrothermal alteration
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Kaidun 角砾岩 CM1 和 CI1 岩性中硫化铁的矿物学：极端至强烈热液蚀变的记录
DOI：
10.1111/maps.12648
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
M. Zolensky
中科院分区：
文献类型：
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作者：
D. Harries;M. Zolensky
多云母凯敦微角砾岩含有C型方解石岩性，具有热液成因的自形硫化铁晶体。我们的FIB-TEM研究表明，CM 1岩性中的针状硫化物由富铁磁黄铁矿和非完整空位超结构（NC-磁黄铁矿）、硫铁矿和镍黄铁矿组成，均显示出明显的出溶结构。基于Fe-Ni-S系统中的相关系，我们将最初均匀的单硫化物固溶体的形成温度限制在100-300 °C的范围内。在某些晶体中，镍黄铁矿的出溶和显微结构平衡是不完全的，可能是由于快速冷却。我们使用热力学模型来约束的物理化学条件的极端热液蚀变在这种岩性。除非CM 1岩性来源于母岩体的大深度（内部压力>85巴）或温度处于所确定的区间的较低范围内，否则水很可能以蒸汽形式存在。之前描述的凯敦CM 1岩性中硫化物的轻δ 34 S组成可能是由于沸腾过程中富含34 S的H2S的损失。相邻的强烈蚀变的CI 1岩性中的片状硫化物晶体由贫铁单斜4C磁黄铁矿和NC磁黄铁矿组成，可能在相对于CM 1岩性的较低温度和较高fS 2下形成。然而，需要更好地理解贫铁磁黄铁矿在低于300 °C的温度下的稳定性，以更好地限制这些条件。
The polymict Kaidun microbreccia contains lithologies of C‐type chondrites with euhedral iron sulfide crystals of hydrothermal origin. Our FIB‐TEM study reveals that acicular sulfides in a CM1 lithology are composed of Fe‐rich pyrrhotite with nonintegral vacancy superstructures (NC‐pyrrhotite), troilite, and pentlandite, all showing distinct exsolution textures. Based on phase relations in the Fe‐Ni‐S system, we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100–300 °C. In some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete, probably due to rapid cooling. We use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology. Unless the CM1 lithology was sourced from a large depth in the parent body (internal pressure >85 bar) or the temperatures were in the lower range of the interval determined, the water was likely present as vapor. Previously described light δ34S compositions of sulfides in Kaidun's CM1 lithology are likely due to the loss of 34S‐enriched H2S during boiling. Platy sulfide crystals in an adjacent, intensely altered CI1 lithology are composed of Fe‐poor, monoclinic 4C‐pyrrhotite and NC‐pyrrhotite and probably formed at lower temperatures and higher fS2 relative to the CM1 lithology. However, a better understanding of the stability of Fe‐poor pyrrhotites at temperatures below 300 °C is required to better constrain these conditions.