HIDALGO: A FUN object from the earliest epoch of the solar system’s history

Abstract

Chemical and isotopic measurements of HIDALGO, a stoichiometrically pure hibonite inclusion found in the matrix of the Dar al Gani 027 meteorite, were conducted by secondary ion mass spectrometry to investigate its origin and evolution. HIDALGO is characterized by large mass-dependent isotope fractionations in O, Ca, and Ti, as well as large negative anomalies in neutron-rich 48Ca and 50Ti, making it the newest member of the HAL-type FUN inclusions. The highly fractionated Ca and Ti isotopes but unfractionated Mg isotopes are consistent with HIDALGO being a residue from an extensive evaporation event, during which large fractions of initial Ca and Ti, and essentially all the initial Mg, in the precursor material were lost. HIDALGO appears to have incorporated live 26Al at a higher level than other HAL-type inclusions, but still at a lower amount compared to the Solar System’s initial 26Al abundance typically found in non-FUN CAIs. Interestingly, the inferred 10Be abundance in HIDALGO is comparable to the values observed in the majority of CV3 CAIs but ∼ 2.5 times higher than those in HAL-type samples. HIDALGO’s unusual 26Al/27Al and 10Be/9Be ratios, together with the 48Ca-50Ti anomalies, can be best explained by the formation of its precursor material in the isotopically heterogeneous solar nebula. Finally, large 7Li excesses correlating with Be/Li were found in HIDALGO, a behavior that can be interpreted as due to in-situ decay of live 7Be. Charged particle spallation of initially Li-free HIDALGO can simultaneously account for the inferred 7Be abundance and the measured Li elemental concentration. The consistency between the measurement and spallation calculation results provides support for the prior existence of 7Be in HIDALGO, possibly produced by irradiation close to the Sun