Acfer 182: search for the location of 15N-enriched nitrogen in an unusual chondrite
Abstract
Acfer 182, an unusual chondrite recovered from the Sahara in 1990, is highly enriched in 15N (bulk δ15N ca.+600‰; δ15N max= +1584‰ at 900°C), reinforcing conclusions that it is related to the very unusual chondrite ALH 85085. Stepped combustion of whole-rock Acfer 182 releases 15N over a wide temperature range, excluding a single carrier phase for the 15N-enriched nitrogen. The highest relative abundance of 15N is found in phase "N C", so far unidentified mineralogically, with a C/N of ca. 8, which releases its nitrogen on combustion of the whole rock at 850-950°C. Attempts to isolate N C by physical means proved unsuccessful. Hence a chemical treatment was tried, with preparation of an HF/HCl-resistant residue. Approximately two-thirds of the original amount of nitrogen in the sample was lost on dissolution. Almost all of component N A, the carbonaceous component, was removed, without significant change in δ15N( +950‰) or C/N ratio (75). N B, originally thought to be nitrogen in metal, was unchanged in abundance, δ15N( +500‰) and C/N ratio (ca. 20), indicating that it could not be present in metal, unless as an insoluble nitride; it might even be an isotopically light entity mixing with residual N A and N C. This last component now combusted at a lower temperature than in the whole rock, and has a lower δ15N value ( +1274‰). A fourth, minor component N D is revealed on combustion of the residue, which burns above 675°C, with δ15N ca.+ 1000‰ and C/N ratio ca. 50. The 15N-enriched nitrogen in almost all constituents of Acfer 182 is interpreted as emanating from a single source, i.e. interstellar grains, which were incorporated within the Acfer 182 parent body during aggregation. Vaporisation, condensation and mixing of components caused redistribution of 15N-enriched nitrogen throughout the parent, with nitrogen either trapped or implanted into silicates and metal.
- Publication:
-
Earth and Planetary Science Letters
- Pub Date:
- April 1993
- DOI:
- 10.1016/0012-821X(93)90052-B
- Bibcode:
- 1993E&PSL.116..165G
- Keywords:
-
- Chondrites;
- Geochemistry;
- Meteoritic Composition;
- Nitrogen Isotopes;
- Carbonates;
- Chemical Analysis;
- Petrology;
- METEORITES;
- ACFER 182;
- SAHARAN METEORITES;
- STONY METEORITES;
- CHONDRITES;
- NITROGEN 15;
- ISOTOPES;
- ENRICHMENT;
- COMPOSITION;
- LABORATORY STUDIES;
- SAMPLES;
- METEORITE;
- ABUNDANCE;
- ORIGIN;
- PROCEDURE;
- GEOCHEMISTRY;
- CARBON;
- FORMATION;
- MINERALOGY;
- CARBONATES;
- ELECTRON MICROSCOPY;
- COMPARISONS;
- HYDROGEN;
- RESIDUE;
- CARRIERS;
- PETROLOGY;
- ANTARCTIC METEORITES;
- WEATHERING;
- ALH METEORITES;
- ALH 85085