The carbon and oxygen isotopic composition of meteoritic carbonates

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90152-4· OSTI ID:5077404

Grady, M M; Wright, I P; Swart, P K; Pillinger, C T ^[1]

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1. Open Univ., Milton Keynes (England)

The {sup 13}C/{sup 12}C and {sup 18}O/{sup 16}O isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on CO{sub 2} released by the action of H{sub 3}PO{sub 4} on whole-rock samples. Carbonates from CI, CM and CR carbonaceous chondrites exhibit a range in {delta}{sup 18}O of ca. 15{per thousand} (+20.5{per thousand} to +35.1{per thousand} relative to SMOW). Limited data from CO{sub 2}-water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous {sup 17}O isotopic compositions; therefore, they are truly enriched in {sup 13}C, with {delta}{sup 13}C between +23.7{per thousand} and +80.7{per thousand} relative to PDB. Large internal variations in {delta}{sup 13}C and {delta}{sup 18}O were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present. The abundance, {delta}{sup 13}C and {delta}{sup 18}O of carbonate in CM2 chondrites may be related to the extent of aqueous alteration of the meteorites. Carbonates in CI and CR chondrites have a median {delta}{sup 13}C ca. +50 to +60{per thousand}, whereas {delta}{sup 13}C of CM meteorites lie in the range +40 to +50 {per thousand}, although exceptions exist in both sets of samples. CV3 and CO3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of CO{sub 2} on acid treatment, which might be from carbonate dissolution, but which is not enriched in {sup 13}C, exhibiting {delta}{sup 13}C values ca. 0 {plus minus} 10{per thousand}. The exception to this is Bishunpur, with {delta}{sup 13}C ca. {minus}23.5{per thousand}. The difference in {delta}{sup 13}C of the CI, CM and CR vs. CV, CO and ordinary chondrite carbonates may be a result of the progressive enrichment in {sup 13}C of percolating fluids, brought about by increasing solubilization of exotic {sup 13}C-enriched grains.

• OSTI ID: 5077404
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:12; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CARBONATES
QUANTITATIVE CHEMICAL ANALYSIS
CHONDRITES
CARBONATE ROCKS
MINERALOGY
CARBON 12
CARBON 13
CHEMICAL COMPOSITION
DISSOLUTION
GEOCHEMISTRY
GEOLOGIC HISTORY
HYDROTHERMAL ALTERATION
ISOTOPE RATIO
MINERALIZATION
OXYGEN 16
OXYGEN 18
PETROLOGY
CARBON COMPOUNDS
CARBON ISOTOPES
CHEMICAL ANALYSIS
CHEMISTRY
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGY
ISOTOPES
LIGHT NUCLEI
METEORITES
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STONE METEORITES
580000* - Geosciences