Oxygen Isotopes in Low-Temperature Minerals of Unequilibrated Chondrites

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WassonEAR-0074076Our main goal is to use the O-isotopes to better understand the evolution of solar nebula and the first generations of chondrite parent bodies. We use ion-probe studies of oxygen isotopes in the phases of the most-primitive chondritic meteorites in order (1) to evaluate the isotopic compositions of oxygen reservoirs in the solar nebula and to gather evidence relating to the spatial and temporal variations in these reservoirs, and (2) to better understand the nature of aqueous alteration processes (that mainly occurred in asteroids) and the nebular source(s) of the asteroidal water. Our work is carried out thin sections, thus we have precise information about the petrographic setting of each probed spot. We examine the O-isotopic evidence regarding changes in the composition of the nebular gas recorded in the chondrules of carbonaceous chondrites and possible models to account for the differences in the O-isotopic composition of chondrules and refractory inclusions. In our studies of aqueous alteration in chondritic asteroids a key phase is magnetite produced by the oxidation of Fe metal, during which all O comes from the oxidant, probably H2O. Thus, the magnetite is a proxy for asteroidal water. We also study chondrule olivine and other alteration phases such as fayalite in order to obtain enough petrographic information to evaluate possible models.