Oxygen Isotopes in Low-Temperature Minerals of Unequilibrated Chondrites

WassonEAR-0074076我们的主要目标是利用氧同位素更好地了解太阳星云和第一代球粒陨石母体的演化。我们使用离子探针研究最原始的球粒陨石相中的氧同位素，目的是(1)评估太阳星云中氧库的同位素组成，并收集与这些库的时空变化有关的证据，(2)更好地了解水蚀变过程(主要发生在小行星上)和小行星水的星云来源(S)的性质。我们的工作是进行薄片，因此我们有关于每个探测点的岩石环境的准确信息。我们考察了记录在碳质球粒陨石球粒中的星云气体组成变化的氧同位素证据，以及解释球粒和难熔包裹体氧同位素组成差异的可能模型。在我们对球粒陨石小行星水蚀变的研究中，一个关键的相是铁金属氧化产生的磁铁矿，在此过程中所有的O都来自氧化剂，可能是H2O。因此，磁铁矿是小行星水的替代品。我们还研究了球粒陨石、橄榄石和其他蚀变相，如铁闪石，以获得足够的岩石学信息来评估可能的模式。

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.