- Names
-
- C.M.O'D. Alexander
- K.T. Howard
- R. Bowden
- M.L. Fogel
- Title
- The classification of CM and CR chondrites using bulk H, C and N abundances and isotopic compositions
- Abstract
- Here we show that bulk H, C and N elemental and isotopic analyses can be used to classify CM and CR chondrites. These meteorites in both groups form well-defined trends in plots of H content vs. dD and C/H vs. dD, and these trends appear to primarily reflect varying degrees of aqueous alteration. The subset of samples with evidence for thermal alteration plot well away from these trends. In CMs, both bulk H and N isotopic compositions, in particular, strongly correlate with petrologic indicators of the degree of alteration and have been used to classify 54 unheated or weakly heated meteorites on a scale of 2–3. However, extrapolation of the trends based on this scale to type 3.0 predicts relatively high water contents, and the schemes cannot be used to classify altered meteorite belonging to other chondrite groups. Here we propose a different classification scheme based on the degree of hydration (wt.% H in water and OH) of a meteorite that can be determined straightforwardly from a meteorite’s bulk H and C contents. Our estimates of the extent of hydration in CMs correlate well with petrologic estimates of the extent of hydration and with the previously determined phyllosilicate abundances. This is not the case for the CRs, which we suggest is due to cryptic alteration of some CRs at low temperatures.
- Keywords
- meteorites, carbonaceous chondrites, CR chondrites, CM chondrites, meteorite PCA 02010, meteorite PCA 02012, meteorite GRA 06100, meteorite GRO 03116, meteorite LEW 85332, meteorite MIL 090001, meteorite ALH 83100, meteorite ALH 84029, meteorite ALH 84034, meteorite ALH 84042, meteorite ALH 84044, meteorite Bells C, meteorite Bells W, meteorite Nogoya, meteorite QUE 93005, meteorite SCO 06043, H, C, N abundances, H, C, N isotopes, classification
- Content
- material-matter, planetary sciences
- Year
- 2013
- Journal
- Geochimica et Cosmochimica Acta
- Volume
- 123
- Pages
- 244 - 260
- Pages number
- 17
- Document type
- article
- Publication state
- published
- Comments
- contains bulk H, C, N elemental and isotopic compositions and classification of 4 CR and 12 CM carbonaceous chondrites