We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
LIME silicates in amoeboid olivine aggregates in carbonaceous chondrites: Indicator of nebular and asteroidal processes.
- Authors
Komatsu, Mutsumi; Fagan, Timothy J.; Mikouchi, Takashi; Petaev, Michail I.; Zolensky, Michael E.
- Abstract
MnO/FeO ratios in olivine from amoeboid olivine aggregates ( AOAs) reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites. LIME (low-iron, Mn-enriched) olivine was identified in AOAs from Y-81020 ( CO3.05), Kaba ( CV~3.1), and in Y-86009 ( CV3), Y-86751 ( CV3), NWA 1152 ( CR/ CV3), but was not identified in AOAs from Efremovka ( CV3.1-3.4) or Allende ( CV>3.6). According to thermodynamic models of nebular condensation, LIME olivine is stable at lower temperatures than Mn-poor olivine and at low oxygen fugacities (dust enrichment <10× solar). Although this set of samples does not represent a single metamorphic sequence, the higher subtypes tend to have AOA olivine with lower Mn/Fe, suggesting that Mn/Fe decreases during parent body metamorphism. Y-81020 has the lowest subtype and most forsteritic AOA olivine (Fo>95) in our study, whereas Efremovka AOAs are slightly Fe-rich (Fo>92). AOA olivines from Kaba are mostly forsteritic, but rare Fe-rich olivine precipitated from an aqueous fluid. A combination of precipitation of Fe-rich olivine and diffusion of Fe into primary olivine grains resulted in iron-rich compositions (Fo97-59) in Allende AOAs. Variations from fine-grained, nonporous matrix toward higher porosity and coarser lath-like matrix olivine can be divided into six stages represented by (1) Y-81020, Efremovka, NWA 1152; (2) Y-86751 lithology B; (3) Y-86009; (4) Kaba; (5) Y-86751 lithology A; (6) Allende. These stages are inferred to represent general degree of metamorphism, although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain.
- Subjects
SILICATES; OLIVINE; CARBONACEOUS chondrites (Meteorites); NEBULAR hypothesis; MANGANESE oxides
- Publication
Meteoritics & Planetary Science, 2015, Vol 50, Issue 7, p1271
- ISSN
1086-9379
- Publication type
Article
- DOI
10.1111/maps.12460