Examination of High Temperature Annealing of Amoeboid Olivine Aggregates: Heating Experiments of Forsterite and Anorthite Mixtures
نویسندگان
چکیده
Introduction: Amoeboid Olivine Aggregates (AOAs) are irregularly-shaped, 100 µm to 5 mm in size, fine-grained objects that constitute a few vol% of meteorites in most carbonaceous chondrite groups. Previous studies concluded that AOAs are aggregates of solar nebula condensates which continued to react with the solar nebula vapor to the temperature to form phyllosilicates. However, these studies are largely from the AOAs from the oxidized CV3 chondrite Allende which experienced secondary alteration. Based on the mineralogical study of the reduced CV3 chondrites, we have recently suggested that AOAs experienced high temperature annealing without substantial melting and were subsequently isolated from high temperature nebular gas, possibly by physical removal, e.g. by X-wind [1]. Annealing and a small degree of melting of AOAs is supported by olivine triple junctions, " doughnut-shaped " forsterite, the presence of rounded FeNi-metal nodules in some AOAs and relatively compact textures. In order to examine the possibility of high-temperature annealing of AOAs, isothermal and cooling experiments of constituent minerals of AOAs have been performed.
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Amoeboid Olivine Aggregates in CR Chondrites
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