A CO-like micrometeorite hosting an exotic Al-Cu-Fe-bearing assemblage – close affinities with the Khatyrka meteorite

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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A CO-like micrometeorite hosting an exotic Al-Cu-Fe-bearing assemblage – close affinities with the Khatyrka meteorite

Messaggio da Marco E. Ciriotti » dom 28 giu, 2020 14:01

Referenza:
▪ Suttle, M.D., Twegar, K., Nava, J., Spiess, R., Spratt, J., Campanale, F., Folco, L. (2019): A unique CO-like micrometeorite hosting an exotic Al-Cu-Fe-bearing assemblage – close affinities with the Khatyrka meteorit. Scientific Reports, 9, 12426.

Abstract:
We report the discovery of a unique micrometeorite, containing an exotic Al-Cu-Fe alloy composed of two intermixed phases: khatyrkite (CuAl2) and stolperite (CuAl) and both containing minor Fe (<1.4 wt%). These phases are dendritic and rapidly co-crystallized at the binary system’s peritectic (~550 °C). The host micrometeorite is an otherwise typical S-type micro-porphyritic cosmic spherule containing relict olivine (Fo76–90, Cr2O3: 0.01–0.56 wt%, MnO: 0.03–0.32 wt% and CaO: 0.09–0.22 wt%) and a cumulate layered texture. These properties suggest the micrometeorite is derived from a carbonaceous chondrite (best matched to a CO chondrite) and entered the atmosphere a high speed (~16 kms−1), implying an origin from a highly eccentric orbit. This particle represents the second independent discovery of naturally occurring intermetallic Al-Cu-Fe alloys and is thus similar to the previously reported Khatyrka meteorite - a CV chondrite containing near-identical alloys and the only known natural quasicrystals. We did not observe quasicrystalline phases in this micrometeorite, likely due to the low amounts of Fe in the alloy, insufficient to stabilize quasicrystals. Our discovery confirms the existence of Al-Cu-Fe intermetallic alloys on chondritic parent bodies. These unusual phases require a currently unexplained formation process, we tentatively suggest this could represent the delivery of exotic interstellar material to the inner solar system via impact.

NdR: a KT01 meteorite, recovered from the Nubian desert (Sudan).
Marco E. Ciriotti

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