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Oxygen isotopic and chemical zoning of melilite crystals in a type A Ca‐Al‐rich inclusion of Efremovka CV3 chondrite
Author(s) -
KAWASAKI Noriyuki,
SAKAMOTO Naoya,
YURIMOTO Hisayoshi
Publication year - 2012
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/maps.12033
Subject(s) - melilite , isotopes of oxygen , chondrite , formation and evolution of the solar system , carbonaceous chondrite , oxygen , geology , nebula , geochemistry , mineralogy , chemistry , meteorite , astrobiology , astrophysics , physics , paleontology , organic chemistry , spinel , stars
– Different oxygen isotopic reservoirs have been recognized in the early solar system. Fluffy type A Ca‐Al‐rich inclusions (CAIs) are believed to be direct condensates from a solar nebular gas, and therefore, have acquired oxygen from the solar nebula. Oxygen isotopic and chemical compositions of melilite crystals in a type A CAI from Efremovka CV3 chondrite were measured to reveal the temporal variation in oxygen isotopic composition of surrounding nebular gas during CAI formation. The CAI is constructed of two domains, each of which has a core‐mantle structure. Reversely zoned melilite crystals were observed in both domains. Melilite crystals in one domain have a homogeneous 16 O‐poor composition on the carbonaceous chondrite anhydrous mineral (CCAM) line of δ 18 O = 5–10‰, which suggests that the domain was formed in a 16 O‐poor oxygen isotope reservoir of the solar nebula. In contrast, melilite crystals in the other domain have continuous variations in oxygen isotopic composition from 16 O‐rich (δ 18 O = −40‰) to 16 O‐poor (δ 18 O = 0‰) along the CCAM line. The oxygen isotopic composition tends to be more 16 O‐rich toward the domain rim, which suggests that the domain was formed in a variable oxygen isotope reservoir of the solar nebula. Each domain of the type A CAI has grown in distinct oxygen isotope reservoir of the solar nebula. After the domain formation, domains were accumulated together in the solar nebula to form a type A CAI.