Abstract
This paper focuses on the post-accretion history of CV3 chondrites, through a combination of petrographic and mineralogical characterization, magnetic measurements, spectral (Raman and Infrared) and thermo-gravimetric analysis of 31 meteorites (including 7 falls, 21 Antarctic and 3 non-Antarctic finds) spanning a wide metamorphic range.
We classify the 21 Antarctic chondrites and the Bukhara fall into the CVRed, CVOxA, and CVOxB subgroups. We establish quantitative parameters relevant for this sub-classification. In comparison to CVOx, CVRed chondrites are characterized by (i) a lower abundance of matrix, (ii) a higher abundance of metal, (iii) the presence of Ni-poor sulfides. In comparison to CVOxB, CVOxA are characterized by (i) similar matrix abundance, (ii) a higher abundance of metal, (iii) the presence of metal almost exclusively under the form of awaruite, (iv) lower Ni content of sulfides, (v) lower magnetic susceptibility and saturation remanence.
Both CVOx (CVOxA and CVOxB) and CVRed experienced aqueous alteration, and contain oxyhydroxides and phyllosilicates. We show that the abundance of these hydrated secondary minerals observed today in individual CV chondrites decreases with their peak metamorphic temperature. This is interpreted either as partial dehydration of these secondary minerals or limited hydration due to the rapid exhaustion of the water reservoir during parent body thermal metamorphism. Moreover, the lower abundance of oxyhydroxides (that have a lower thermal stability than phyllosilicates and may in large part postdate the peak of thermal metamorphism) in more metamorphosed CV chondrites is interpreted as lower availability of aqueous fluids during retrograde metamorphism in these meteorites.
Lastly, we show that in comparison to CVOxB, CVOxA are systematically (i) more metamorphosed, (ii) less hydrated, (iii) depleted in ferromagnetic minerals, (iv) but enriched in metal in the form of secondary awaruite. CVOxA may be thermally metamorphosed CVOxB. CVRed are significantly different from CVOx (matrix abundances, alteration products, opaque minerals), but span the same wide metamorphic range. This could be indicative of a laterally heterogeneous CV parent body, or suggest the existence of distinct parent bodies for CVOx and CVRed chondrites.
We classify the 21 Antarctic chondrites and the Bukhara fall into the CVRed, CVOxA, and CVOxB subgroups. We establish quantitative parameters relevant for this sub-classification. In comparison to CVOx, CVRed chondrites are characterized by (i) a lower abundance of matrix, (ii) a higher abundance of metal, (iii) the presence of Ni-poor sulfides. In comparison to CVOxB, CVOxA are characterized by (i) similar matrix abundance, (ii) a higher abundance of metal, (iii) the presence of metal almost exclusively under the form of awaruite, (iv) lower Ni content of sulfides, (v) lower magnetic susceptibility and saturation remanence.
Both CVOx (CVOxA and CVOxB) and CVRed experienced aqueous alteration, and contain oxyhydroxides and phyllosilicates. We show that the abundance of these hydrated secondary minerals observed today in individual CV chondrites decreases with their peak metamorphic temperature. This is interpreted either as partial dehydration of these secondary minerals or limited hydration due to the rapid exhaustion of the water reservoir during parent body thermal metamorphism. Moreover, the lower abundance of oxyhydroxides (that have a lower thermal stability than phyllosilicates and may in large part postdate the peak of thermal metamorphism) in more metamorphosed CV chondrites is interpreted as lower availability of aqueous fluids during retrograde metamorphism in these meteorites.
Lastly, we show that in comparison to CVOxB, CVOxA are systematically (i) more metamorphosed, (ii) less hydrated, (iii) depleted in ferromagnetic minerals, (iv) but enriched in metal in the form of secondary awaruite. CVOxA may be thermally metamorphosed CVOxB. CVRed are significantly different from CVOx (matrix abundances, alteration products, opaque minerals), but span the same wide metamorphic range. This could be indicative of a laterally heterogeneous CV parent body, or suggest the existence of distinct parent bodies for CVOx and CVRed chondrites.
| Original language | English |
|---|---|
| Pages (from-to) | 363-383 |
| Number of pages | 21 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 276 |
| DOIs | |
| Publication status | Published - May 2020 |
Bibliographical note
Funding Information:US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institutions and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center. We acknowledge sample loans from the Field Museum (Chicago, IL), the Natural History Museum (London), and the Museum d'Histoire Naturelle (Paris). We also thank Kevin Righter and John Schutt for answering our questions regarding pairing of Antarctic meteorites. This work has been funded by the Centre National d'Etudes Spatiales (CNES–France). The Raman facility in Lyon is supported by the Institut National des Sciences de l'Univers (INSU–France). We thank two anonymous reviewers, Dr. Adrian Brearley and Dr. Sasha Krot (Assistant Editor) for their careful reviews and relevant comments.
Funding Information:
US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institutions and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center. We acknowledge sample loans from the Field Museum (Chicago, IL), the Natural History Museum (London), and the Museum d’Histoire Naturelle (Paris). We also thank Kevin Righter and John Schutt for answering our questions regarding pairing of Antarctic meteorites. This work has been funded by the Centre National d’Etudes Spatiales (CNES–France). The Raman facility in Lyon is supported by the Institut National des Sciences de l’Univers (INSU–France). We thank two anonymous reviewers, Dr. Adrian Brearley and Dr. Sasha Krot (Assistant Editor) for their careful reviews and relevant comments.
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