Terrestrial modification of the Ivuna meteorite and a reassessment of the chemical composition of the CI type specimen
Terrestrial modification of the Ivuna meteorite and a reassessment of the chemical composition of the CI type specimen
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伊武纳陨石的陆地改造和 CI 型标本化学成分的重新评估
DOI：
10.1016/j.gca.2019.09.041
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发表时间：
2020
影响因子：
5
通讯作者：
King A
中科院分区：
文献类型：
--
作者：
King A
稀有的CI碳质陨石是最具水蚀变和化学原始的陨石，但由于其多孔性和高丰度的挥发性元素，容易受到陆地风化。伊武纳陨石是CI陨石的典型标本，是20世纪最大的CI陨石坠落，也可能是可供研究的受陆地蚀变影响最小的CI球粒陨石。Ivuna的主体（BM 2008 M1）至少在2008年（坠落后70年）抵达伦敦自然历史博物馆（NHM）后一直储存在氮气气氛中，可以被认为是最原始的CI球粒陨石。我们报告的矿物学，岩相学和散装元素组成的BM 2008 M1和第二个Ivuna石（BM 1996 M4）存储在空气中的木柜。我们发现，这两个伊武纳石头的角砾岩组成的多个圆形，层状硅酸盐丰富的碎屑，通过水蚀变，然后冲击加工形成。在制备后立即分析的BM 2008 M1的抛光薄片被发现含有原生硫化物与氧气和大气水反应时形成的含硫酸盐矿脉。BM 1996 M4的一个剖面没有脉，但表面有硫酸盐颗粒，形成时间≤6年，比之前报道的CI球粒陨石剖面快1.3倍。BM 2008 M1和BM 1996 M4记录的陆地蚀变程度的差异可能反映了在进入NHM收集之前石头的恢复后管理历史的变化，并表明在可能的情况下，水合碳质的原始样品应保持在稳定的大气中，以避免修改的陆地环境。两个Ivuna石头的散装元素组成显示出一定的变异性，由于其异质性，但在一般情况下，类似于以前的分析CI钙钛矿。我们结合联合收割机我们的元素丰度与文献值计算一个新的平均组成的Ivuna陨石，我们发现是在良好的协议与现有的汇编的元素组成的CI陨石和最近的太阳光球丰度。
The rare CI carbonaceous chondrites are the most aqueously altered and chemically primitive meteorites but due to their porous nature and high abundance of volatile elements are susceptible to terrestrial weathering. The Ivuna meteorite, type specimen for the CI chondrites, is the largest twentieth-century CI fall and probably the CI chondrite least affected by terrestrial alteration that is available for study. The main mass of Ivuna (BM2008 M1) has been stored in a nitrogen atmosphere at least since its arrival at the Natural History Museum (NHM), London, in 2008 (70 years after its fall) and could be considered the most pristine CI chondrite stone. We report the mineralogy, petrography and bulk elemental composition of BM2008 M1 and a second Ivuna stone (BM1996 M4) stored in air within wooden cabinets. We find that both Ivuna stones are breccias consisting of multiple rounded, phyllosilicate-rich clasts that formed through aqueous alteration followed by impact processing. A polished thin section of BM2008 M1 analysed immediately after preparation was found to contain sulphate-bearing veins that formed when primary sulphides reacted with oxygen and atmospheric water. A section of BM1996 M4 lacked veins but had sulphate grains on the surface that formed in ≤6 years, ∼3 times faster than previous reports for CI chondrite sections. Differences in the extent of terrestrial alteration recorded by BM2008 M1 and BM1996 M4 probably reflect variations in the post-recovery curation history of the stones prior to entering the NHM collection, and indicate that where possible pristine samples of hydrated carbonaceous should be kept out of the terrestrial environment in a stable atmosphere to avoid modification. The bulk elemental composition of the two Ivuna stones show some variability due to their heterogeneous nature but in general are similar to previous analyses of CI chondrites. We combine our elemental abundances with literature values to calculate a new average composition for the Ivuna meteorite, which we find is in good agreement with existing compilations of element compositions in the CI chondrites and the most recent solar photospheric abundances.
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南极陨石中的粘土矿物风化产物
影响因子：
5
作者：
J. Gooding
通讯作者：
J. Gooding
影响因子：
5
作者：
Lee, MR;Bland, PA
通讯作者：
Bland, PA
影响因子：
5
作者：
King, A. J.;Schofield, P. F.;Russell, S. S.
通讯作者：
Russell, S. S.
影响因子：
5
作者：
Bullock, ES;Gounelle, M;Russell, SS
通讯作者：
Russell, SS
LPSC XXIII 153 IVUNA CI 碳质岩中细粒基质的矿物学
DOI：
--
发表时间：
2009
期刊：
影响因子：
--
作者：
C. Adrian
通讯作者：
C. Adrian