The nanoscale mineralogy of Fe,Ni sulfides in pristine and metamorphosed CM and CM/CI‐like chondrites: Tapping a petrogenetic record
The nanoscale mineralogy of Fe,Ni sulfides in pristine and metamorphosed CM and CM/CI‐like chondrites: Tapping a petrogenetic record
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原始和变质 CM 和 CM/CI 类球粒陨石中 Fe、Ni 硫化物的纳米矿物学：挖掘岩石成因记录
DOI：
10.1111/maps.12089
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发表时间：
2013
影响因子：
2.2
通讯作者：
F. Langenhorst
中科院分区：
文献类型：
--
作者：
D. Harries;F. Langenhorst
我们用聚焦离子束技术采集了一个原始的CM_2球粒陨石(Yamato[Y-]791198)、一个热变质的CM_2球粒陨石(Y-793321)和两个异常变质的类CM/CI球粒陨石(Y-86720和Belgica[B-]7904)的硫化物颗粒，并用分析电子显微镜对其进行了研究。我们的研究旨在探索硫化物组合和微构造对球粒陨石形成过程和条件的解释潜力。在Y-791198和Y-793321的颗粒中存在磁黄铁矿(晶体NC型，N≈6)、硫铁矿和镍黄铁矿的复杂出溶结构。此外，在Y-791198中还出现了多晶4C-磁黄铁矿-镍黄铁矿-磁铁矿集合体，这表明太阳星云中存在不同的气固相互作用条件。Y-793321颗粒较粗的出溶结构表明，与Y-791198和其他CM球粒陨石相比，<；100°C范围内的长期平均温度更高。Y-86720和B-7904型硫化物矿物学以纯硫铁闪石和金属的集合体为主，表明铁-硫铁闪锌矿缓冲液的硫逸度(Fs2)为变质平衡。Y-86720缺乏与硫化物和金属平衡的磁铁矿，指示比B-7904更高的峰温，其中硫铁矿、金属和磁铁矿的共存将变质温度限制在570℃以下。NC-磁黄铁矿以纳米宽的边缘出现在硫铁矿颗粒上，并与频繁的硬石膏一起指示在铁闪石-磁铁矿-石英-磁黄铁矿缓冲层上方较高的Fs2处的退变阶段。两块陨石中的细粒硫铁矿-橄榄石交互生长表明，变质前存在托吉林石-蛇纹石夹层相，表明矿物学上的CM亲和力。Y-86720中的正面体磁黄铁矿晶体后的假形态又表明了CI亲和性，这与之前发表的两块陨石的氧同位素数据一样。
We have sampled sulfide grains from one pristine CM2 chondrite (Yamato [Y‐] 791198), one thermally metamorphosed CM2 chondrite (Y‐793321), and two anomalous, metamorphosed CM/CI‐like chondrites (Y‐86720 and Belgica [B‐] 7904) by the focused ion beam (FIB) technique and studied them by analytical transmission electron microscopy (TEM). Our study aims at exploring the potential of sulfide assemblages and microstructures to decipher processes and conditions of chondrite petrogenesis. Complex exsolution textures of pyrrhotite (crystallographic NC‐type with N ≈ 6), troilite, and pentlandite occur in grains of Y‐791198 and Y‐793321. Additionally, polycrystalline 4C‐pyrrhotite‐pentlandite‐magnetite aggregates occur in Y‐791198, pointing to diverse conditions of gas–solid interactions in the solar nebula. Coarser exsolution textures of Y‐793321 grains indicate higher long‐term average temperatures in the <100 °C range compared to Y‐791198 and other CM chondrites. Sulfide mineralogy of Y‐86720 and B‐7904 is dominated by aggregates of pure troilite and metal, indicating metamorphic equilibration at sulfur fugacities (fS2) of the iron‐troilite buffer. Absence of magnetite in equilibrium with sulfide and metal in Y‐86720 indicates higher peak temperatures compared with B‐7904, in which coexistence of troilite, metal, and magnetite constrains metamorphic temperature to less than 570 °C. NC‐pyrrhotite occurs in both meteorites as nm‐wide rims on troilite grains and, together with frequent anhydrite, indicates a retrograde metamorphic stage at higher fS2 slightly above the fayalite‐magnetite‐quartz‐pyrrhotite buffer. Fine‐grained troilite‐olivine intergrowths in both meteorites suggest the pre‐metamorphic presence of tochilinite‐serpentine interlayer phases, pointing to mineralogical CM affinity. Pseudomorphs after euhedral pyrrhotite crystals in Y‐86720 in turn suggest CI affinity as do previously published O isotopic data of both meteorites.