Fe and O isotope composition of meteorite fusion crusts: Possible natural analogues to chondrule formation?

Abstract

Meteorite fusion crust formation is a brief event in a high‐temperature (2000–12,000 K) and high‐pressure (2–5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with δ56Fe values up to +0.35‰ relative to the solar system mean. On average, the δ56Fe of fusion crusts from finds is +0.23‰, which is 0.08‰ higher than the average from falls (+0.15‰). Higher δ56Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The δ56Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher δ18O (0.9–1.5‰) than their host chondrites, and the same is true for Δ17O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high‐pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16O‐poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.

Highly Siderophile Elements and Coupled Fe-Os Isotope Signatures in the Temagami Iron Formation, Canada: Possible Signatures of Neoarchean Seawater Chemistry and Earth's Oxygenation History

“…Both, samples and standards were doped with the same Cu standard solution to achieve 1 ppm Cu in the measurement solutions, which was used to correct for mass bias. More detailed descriptions on sample preparation and mass spectrometry are given in the work of Hezel et al (2010Hezel et al ( , 2015.…”

To be or not to be oxidized: A case study of olivine behavior in the fusion crust of ureilite A 09368 and H chondrites A 09004 and A 09502

“…There is renewed interest in meteorite fusion crust because it could serve as a potential analog for chondrule formation, by comparison between meteorite ablation spherules, cosmic spherules, and chondrules, implying a similar melting and ablation process (Genge ), and due to similarities in Fe and O isotope composition between meteorite fusion crust and chondrules (Hezel et al. ). In addition, as already proposed by El Goresy and Fechtig () and Genge and Grady (), the processes operating in the newly forming fusion crust and their relationship with the unaffected interior of the meteorite replicate those occurring in cosmic spherules during the atmospheric entry, and thus provide a key to understanding the formation of micrometeorites.…”

Parentage Identification of Differentiated Achondritic Meteorites by Hand‐held Energy Dispersive X‐Ray Fluorescence Spectrometry

“…Hezel et al . () show, in fact, that the fusion crust of ordinary chondrites is enriched in heavy Fe ( 56 Fe) and O isotopes ( 18 O) as a result of kinetic fractionation during evaporation.…”

“…Mineralogical and geochemical studies of meteorite fusion crusts (i.e., Genge and Grady 1999) demonstrate that compositional differences relative to whole rock are the result of complex processes, which, besides oxidation, include evaporative loss of volatile elements. Hezel et al (2015) show, in fact, that the fusion crust of ordinary chondrites is enriched in heavy Fe ( 56 Fe) and O isotopes ( 18 O) as a result of kinetic fractionation during evaporation.…”