| الوصف: |
HIDALGO, a ~300×300 μm, hexagonally shaped, chemically and mineralogically simple hibonite crystal residing in the matrix of the CO3 chondrite Dar al Gani 027 (DaG027), is the newest member in the FUN-hibonite family. Based on the mass-dependent fractionations in O, Ca, and Ti isotopes, large negative anomalies in δ48Ca (= −30‰) and δ50Ti (= −20‰), and the abundances of short-lived radioisotopes of 10Be, 26Al, 41Ca, which have all been reported previously, we have inferred that HIDALGO evolved from a condensate that most likely formed before 26Al was built up and homogenized to 26Al/27Al = 5.2×10−5 in the solar system. This precursor also incorporated 10Be at the level of 10Be/9Be = 7.5×10−4, possibly through local irradiation of gas and/or dust or inheritance from the molecular cloud, but the amount of 41Ca present at that time and location is uncertain. Strong heating of the precursor occurred ~0.5 Myr after the initial condensation, leading to total melting accompanied by extensive distillation (losing Mg, Si, and other moderately volatile elements) resulting in a stoichiometrically pure hibonite crystal with strongly mass fractionated O, Ca, and Ti isotope compositions and an extreme Ce depletion relative to other REEs. Here we report the results of Li isotope analyses of HIDALGO and discuss the irradiation history of this inclusion. |
