Abstract
We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al2O3, occurring where silicate melt was in contact with Al-Cu-Fe alloys. In the reaction zone, there are metallic Fe and Fe-Si beads, aluminous spinel rinds on the Al-Cu-Fe alloys, and Al2O3 enrichment in the silicate melt surrounding the alloys. From this and other evidence, we demonstrate that Khatyrka must have experienced at least two distinct events: first, an event as early as 4.564 Ga in which the first Al-Cu-Fe alloys formed; and, second, a more recent impact-induced shock in space that led to transformations of and reactions between the alloys and the meteorite matrix. The new evidence firmly establishes that the Al-Cu-Fe alloys (including quasicrystals) formed in outer space in a complex, multi-stage process.
Highlights
The Khatyrka meteorite[1, 2], an oxidized-subgroup (Allende-like) CV3 carbonaceous chondrite, contains silicates and oxides that are typical of CV3 chondrites[3,4,5,6,7]
The unexpected occurrence of these phases in nature has motivated a multidisciplinary effort to understand the physical and chemical history of the Khatyrka meteorite for the purpose of revealing heretofore-unknown conditions and physical processes in the solar nebula and providing insights into the formation and stability of quasicrystals in nature
We assume for the purposes of simplicity that a single shock event is associated with the production of the high-pressure phases in 126 and in other grains, as well as with the silicate melt and redox reaction observed in 126A
Summary
The Khatyrka meteorite[1, 2], an oxidized-subgroup (Allende-like) CV3 carbonaceous chondrite, contains silicates and oxides that are typical of CV3 (ox) chondrites[3,4,5,6,7]. Earlier investigations of Khatyrka have produced abundant petrologic and chemical evidence showing that Khatyrka experienced at least one high-velocity impact event[21, 22] This includes the observation of two high-pressure Fe-bearing phases: ahrensite (Fe2SiO4)[23] and an unnamed oxide with composition Fe2.6Si0.4O4 that has the structure of spinelloid V24. Measurements of noble gas cosmogenic nuclides in the olivine of 126 show that the most recent major impact event experienced by Khatyrka occurred in space a few 100 Ma18, 19 and produced shocks consistent with the range S3 to S5 (though probably closer to S4), corresponding to approximately 10–35 GPa25 An impact of this magnitude could account for the high-pressure phases, as well as the silicate melt and reactions that we report . Because there is currently no evidence to the contrary, we will assume this is the case for the purpose of this discussion, referring only to a single ‘impact event’ occurring a few 100 Ma, while acknowledging that we could be observing the results of a series of impact events occurring over eons of time
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