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Cr isotopes in physically separated components of the Allende CV 3 and Murchison CM 2 chondrites: Implications for isotopic heterogeneity in the solar nebula and parent body processes
Author(s) -
Kadlag Yogita,
Becker Harry,
Harbott Andreas
Publication year - 2019
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.13375
Subject(s) - murchison meteorite , allende meteorite , chondrule , chondrite , meteorite , formation and evolution of the solar system , carbonaceous chondrite , parent body , geology , isotope , nebula , geochemistry , mineralogy , astrobiology , analytical chemistry (journal) , chemistry , astrophysics , environmental chemistry , physics , stars , quantum mechanics
Abstract Chromium isotopic data of physically separated components (chondrules, CAI s, variably magnetic size fractions) of the carbonaceous chondrites Allende and Murchison and bulk rock data of Allende, Ivuna, and Orgueil are reported to evaluate the origin of isotopic heterogeneity in these meteorites. Allende components show ε 53 Cr and ε 54 Cr from −0.23 ± 0.07 to 0.37 ± 0.05 and from −0.43 ± 0.08 to 3.7 ± 0.1, respectively. In components of Murchison, ε 53 Cr and ε 54 Cr vary from −0.06 ± 0.08 to 0.5 ± 0.1 and from 0.7 ± 0.2 to 1.7 ± 0.1, respectively. The non‐systematic variations of ε 53 Cr and 55 Mn/ 52 Cr in the components of Allende and Murchison were likely caused by small‐scale, alteration‐related redistribution of Mn >20 Ma after formation of the solar system. Chondrule fractions show the lowest 55 Mn/ 52 Cr and ε 54 Cr values of all components, consistent with evaporation of Mn and ε 54 Cr‐rich carrier phases from chondrule precursors. Components other than the chondrules show higher Mn/Cr and ε 54 Cr, suggestive of chemical and isotopic complementarity between chondrules and matrix‐rich fractions. Bulk rock compositions calculated based on weighted compositions of components agree with measured Cr isotope data of bulk rocks, in spite of the Cr isotopic heterogeneity reported by the present and previous studies. This indicates that on a sampling scale comprising several hundred milligrams, these meteorites sampled isotopically and chemically homogeneous nebular reservoirs. The linear correlation of 55 Mn/ 52 Cr with ε 53 Cr in bulk rocks likely was caused by variable fractionation of Mn/Cr, subsequent mixing of phases in nebular domains, and radiogenic ingrowth of 53 Cr.