Deuterium in carbonaceous chondrites

Hydrogen isotopic compositions in seven carbonaceous chondrites lie in the range −70 to +771‰ relative to SMOW. These values decrease, to a range from −145 to +219‰, after low-temperature oxidation in an oxygen plasma. Deuterium enrichment is therefore concentrated in the organic matter, the hydrous silicates probably lying close to the terrestrial range for such material. Calculated values for δD of the organic fraction are +450 ‰ for Orgueil and Ivuna and up to +1600‰ for Renazzo. These enrichments, at least for Orgueil and Ivuna, suggest equilibration with protosolar hydrogen at very low temperatures. Assuming a value of 2.5 × 10 −5 for the protosolar D/H ratio, nominal equilibration temperatures of 230°K for silicates and 180°K for organic matter may be derived.