The iron record of asteroidal processes in carbonaceous chondrites
| Autor: | Pierre Beck, A. Garenne, German Montes-Hernandez, Jean-Louis Hazemann, Eric Quirico, Olivier Proux, Lydie Bonal |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Earth and Planetary Astrophysics (astro-ph.EP)
Valence (chemistry) Aqueous solution Analytical chemistry FOS: Physical sciences 010502 geochemistry & geophysics 01 natural sciences Redox Silicate Metal Petrography chemistry.chemical_compound Geophysics chemistry Space and Planetary Science Chondrite visual_art 0103 physical sciences visual_art.visual_art_medium 010303 astronomy & astrophysics 0105 earth and related environmental sciences Magnetite Astrophysics - Earth and Planetary Astrophysics |
| Zdroj: | Meteoritics & Planetary Science |
| DOI: | 10.48550/arxiv.2009.13950 |
| Popis: | The valence of iron has been used in terrestrial studies to trace the hydrolysis of primary silicate rocks. Here, we use a similar approach to characterize the secondary processes, namely thermal metamorphism and aqueous alteration, that have affected carbonaceous chondrites. X-ray absorption near-edge structure spectroscopy at the Fe-K- edge was performed on a series of 36 CM, 9 CR, 10 CV, and 2 CI chondrites. Among the four carbonaceous chondrites groups studied, a correlation between the iron oxidation index (IOI = [2 ((Fe2+) + 3(Fe3+))/FeTOT) and the hydrogen content is observed. However, within the CM group, for which a progressive alteration sequence has been defined, a conversion of Fe3+ to Fe2+ is observed with increasing degree of aqueous alteration. This reduction of iron can be explained by an evolution in the mineralogy of the secondary phases. In the case of the few CM chondrites that experienced some thermal metamorphism, in addition to aqueous alteration, a redox memory of the aqueous alteration is present: a significant fraction of 3+ 2+ 0 Fe is present, together with Fe and sometimes Fe. From our data set, the CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR chondrites, the three oxidation states of iron coexist. Even in the least-altered CR chondrites, the fraction of Fe3+ can be high (30% for MET 00426). This observation confirms that oxidized iron has been integrated during formation of fine-grained amorphous material in the matrix. Last, the IOI of CV chondrites does not reflect the reduced/oxidized classification based on metal and magnetite proportions, but is strongly correlated with petrographic types. The valence of iron in CV chondrites therefore appears to be most closely related to thermal history, rather than aqueous alteration, even if these processes can occur together . |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|