TY - JOUR
T1 - Condensation and aggregation of solar corundum and corundum-hibonite grains
AU - Nakamura, T. M.
AU - Sugiura, N.
AU - Kimura, M.
AU - Miyazaki, A.
AU - Krot, A. N.
PY - 2007
Y1 - 2007
N2 - Forty-three corundum grains (1-11 μm in size) and 5 corundum-hibonite grains with corundum overgrown by hibonite (4-7 μm in size), were found in the matrix of the mineralogically pristine, ungrouped carbonaceous chondrite Acfer 094 by using cathodoluminescence imaging. Some of the corundum and corundum-hibonite grains occur as aggregates of 2 to 6 grains having similar sizes. The oxygen isotopic compositions of some of the corundum-bearing grains suggest their solar nebula origin. 26Al-26Mg systematics of one corundum grain showed the canonical initial 26Al/27Al ratio, also suggesting a solar nebula origin. Quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum, diffusion-controlled hibonite formation, collisions of grains in the nebula, and critical velocity for sticking, indicates that, in contrast to the hibonite-bearing aggregates of corundum grains, the hibonite-free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition. We suggest instead that such aggregates formed near the protosun, either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated, Ca-depleted region, and were subsequently physically removed from this hot region, e.g., by disk wind.
AB - Forty-three corundum grains (1-11 μm in size) and 5 corundum-hibonite grains with corundum overgrown by hibonite (4-7 μm in size), were found in the matrix of the mineralogically pristine, ungrouped carbonaceous chondrite Acfer 094 by using cathodoluminescence imaging. Some of the corundum and corundum-hibonite grains occur as aggregates of 2 to 6 grains having similar sizes. The oxygen isotopic compositions of some of the corundum-bearing grains suggest their solar nebula origin. 26Al-26Mg systematics of one corundum grain showed the canonical initial 26Al/27Al ratio, also suggesting a solar nebula origin. Quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum, diffusion-controlled hibonite formation, collisions of grains in the nebula, and critical velocity for sticking, indicates that, in contrast to the hibonite-bearing aggregates of corundum grains, the hibonite-free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition. We suggest instead that such aggregates formed near the protosun, either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated, Ca-depleted region, and were subsequently physically removed from this hot region, e.g., by disk wind.
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U2 - 10.1111/j.1945-5100.2007.tb00572.x
DO - 10.1111/j.1945-5100.2007.tb00572.x
M3 - Article
AN - SCOPUS:36348977360
VL - 42
SP - 1249
EP - 1265
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 7-8
ER -