Calcium-aluminum-rich inclusions with fractionation and unknown nuclear effects (FUN CAIs): I. Mineralogy, petrology, and oxygen isotopic compositions

摘要: We present a detailed characterization of the mineralogy, petrology, and oxygen isotopic compositions twelve FUN CAIs, including C1 EK1-4-1 from Allende (CV), that were previously shown to have large fractionation patterns for magnesium oxygen, anomalies several elements. The other samples show more modest smaller but significant anomalies. All CAIs studied are coarse-grained igneous inclusions: Type B, forsterite-bearing compact A, hibonite-rich. Some inclusions consist two mineralogically distinct lithologies, forsterite-rich forsterite-free/poor. CV experienced postcrystallization open-system iron-alkali-halogen metasomatic alteration resulting in formation secondary minerals commonly observed non-FUN chondrites. CR CAI GG#3 shows no evidence alteration. In all samples, clear was found. Most initially ^(16)O-rich. On three-oxygen isotope diagram, various each (spinel, forsterite, hibonite, dmisteinbergite, most fassaite grains, melilite (only GG#3)), define mass-dependent lines with similar slope ∼0.5. different Δ^(17)O values ranging ∼−25‰ ∼−16‰. Melilite plagioclase ^(16)O-poor (Δ^(17)O ∼−3‰) plot near intercept line terrestrial line. infer effects isotopes due evaporation during melt crystallization. Differences defined by individual inferred reflect differences their precursors. δ^(18)O defining consistent crystallization sequence, suggesting these crystallized evaporation. correlation between sequence is observed, possibly indicating gas-melt back reaction oxygen-isotope exchange ^(16)O-rich gaseous reservoir. After fractionation, some could partial melting reservoir resulted ^(16)O-depleted fassaite, plagioclase. final may been established on parent asteroid as result fluid hydrothermal We conclude part general family refractory showing degrees evaporative processes superimposed sampling isotopically heterogeneous material. These both CAIs. Generally, identified larger than There wide spread UN number not exhibiting magnesium, silicon. question why extreme attributed us limited special source anomalous consider majority be stages thermal processing (evaporation, condensation, melting) aggregates solid precursors composed incompletely homogenized materials. unknown nuclear common characteristic represent spectrum results very medium accreting Solar System.