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The White Angel: A unique wollastonite‐bearing, mass‐fractionated refractory inclusion from the Leoville CV3 carbonaceous chondrite
Author(s) -
Komorowski Catherine L. V. Caillet,
Zinner Ernst K.,
McKeegan Kevin D.,
Hervig Rick,
Buseck Peter R.
Publication year - 2007
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2007.tb00567.x
Subject(s) - chondrite , trace element , geology , melt inclusions , carbonaceous chondrite , meteorite , wollastonite , mineral , parent body , mineralogy , refractory (planetary science) , geochemistry , analytical chemistry (journal) , chemistry , olivine , astrobiology , environmental chemistry , raw material , physics , organic chemistry
— We report the study of an unusual compact type A refractory inclusion, named the White Angel, from the Leoville CV3 meteorite. The petrologic, mineral chemical, isotopic, and trace‐element signatures of this once‐molten Ca‐Al‐rich inclusion (CAI), which contains large, equant wollastonite crystals, indicate a short multistage history that occurred very early, before substantial decay of 26 Al. Magnesium in the inclusion is isotopically heavy, with F Mg reaching 18‰/amu, in the range of fractionated and with unidentified nuclear effects (FUN) inclusions. However, the absence of any nuclear anomalies in Ca and Ti and an inferred 26 Al/ 27 Al ratio of (5.5 ± 0.9) × 10 −5 indicate that the White Angel belongs to the F inclusions. Silicon and oxygen are also mass fractionated in favor of the heavy isotopes, but to a lesser extent. The O isotopes show a range in 16 O excesses. On an O three‐isotope plot, data points lie on a line parallel and to the right of the carbonaceous chondrite anhydrous mineral mixing line, with wollastonite being the most 16 O‐rich phase. The chondrite‐normalized rare earth and trace‐element pattern of the whole inclusion is the complement of an ultrarefractory pattern indicating that precursor phases of the CAI must have condensed in an Al‐, heavy rare earth element (HREE)‐depleted reservoir. Melting of those precursor phases in an 16 O‐rich environment and evaporation led to mass‐dependent isotopic fractionation of Mg, Si, and O. Partial isotopic exchange with a reservoir containing unfractionated Mg took place at a later stage but before any measurable decay of 26 Al. Some minerals (melilite and perovskite) in the White Angel equilibrated oxygen isotopes with a relatively 16 O‐poor reservoir that was also mass‐fractionated toward the heavy isotopes, different from that with which the normal or FUN inclusions interacted.