Publication
- Names
-
- L. Bonal
- G.R. Huss
- A.N. Krot
- K. Nagashima
- H.A. Ishii
- J.P. Bradley
- Title
- Highly 15N-enriched chondritic clasts in the CB/CH-like meteorite Isheyevo
- Abstract
- The metal-rich carbonaceous chondrites (CB and CH) have the highest whole-rock 15N-enrichments (δ15N up to 1500‰) among planetary materials. They are also characterized by the absence of interchondrule fine-grained matrix. The only fine-grained material is present as lithic clasts, which experienced extensive aqueous alteration in contrast to the surrounding high-temperature components (chondrules, refractory inclusions, metal grains). Hence, the clasts are foreign objects that were incorporated at a late stage into the final parent body of Isheyevo. Their origin is poorly constrained. Based on mineralogy, petrography, and thermal processing of the aromatic carbonaceous component, different types of clasts have been previously identified in the CB/CH-like chondrite Isheyevo. Here, we focus on the rare lithic clasts characterized by the presence of anhydrous silicates (chondrules, chondrule fragments, and CAIs). Their mineralogy and oxygen isotopic compositions reveal them to be micro-chondrules, fragments of chondrules, and refractory inclusions related to those in the Isheyevo host, suggesting accretion in the same region. In contrast to previously studied IDPs or primitive chondritic matrices, the fine-grained material in the clasts we studied is highly and rather uniformly enriched in heavy nitrogen, with bulk δ15N values ranging between 1000‰ and 1300‰. It is also characterized by the presence of numerous 15N hotspots (δ15N ranging from 1400‰ to 4000‰). No bulk (δD <–240‰) or localized deuterium enrichments were observed. These clasts have the highest bulk enrichment in heavy nitrogen measured to date in a fine-grained material. They represent a unique material, of asteroidal or cometary origin, in our collection of cosmomaterials. We show that they were 15N-enriched before their incorporation in the final parent body of Isheyevo. They experienced an extensive aqueous alteration that most likely played a role in redistributing 15N over the whole fine-grained material and may have significantly modified its initial hydrogen isotopic composition. Based on a review of isotopic fractionation models, we conclude that the nitrogen isotopic fractionation process, its timing, and its location are still poorly constrained. The 15N-rich clasts may represent the surviving original carrier of the 15N anomaly in Isheyevo whole-rock.
- Keywords
- spectroscopy, Raman micro-spectrometer, Raman spectra, carbonaceaous chondrites, meteorite Isheyevo
- Content
- material-matter, spectral data, planetary sciences
- Year
- 2010
- Journal
- Geochimica et Cosmochimica Acta
- Volume
- 74
- Number
- 22
- Pages
- 6590 - 6609
- Pages number
- 21
- Document type
- article
- Publication state
- published
- Doi
- 10.1016/j.gca.2010.08.017
- Identifiers