隕石母天体の集積の歴史を明らかにする試み(2012年度日本地球化学会賞受賞記念論文)

概要

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Accretion ages of meteorite parent bodies were estimated assuming homogeneous distribution of ^<26>Al in the solar nebula. In case of iron meteorites, the accretion ages are constrained by the core formation ages (W isotopic composition of metal samples). In case of achondrites, Al-Mg and Mn-Cr ages obtained from (bulk) isochrons and/or Mg isotopic compositions of Al-poor meteorites could be used for constraining accretion ages. In case of chondrite parent bodies, the accretion ages are mainly constrained by the peak metamorphic temperatures. Formation ages of secondary minerals such as carbonates also constrain accretion ages of C chondrite parent bodies. Using literature data of bulk ε^<54>Cr anomalies in meteorites and the estimated accretion ages, a diagram that suggests increase in ε^<54>Cr with time of accretion is constructed. This is interpreted as a result of injection of ^<54>Cr-rich grains into the solar nebula and the subsequent diffusive advection. Numerical simulations confirmed that the ε^<54>Cr evolution obtained from meteoritic data can be well explained by an appropriate set of adjustable parameters (e.g. viscosity parameter=10^<-3> and injection radius〜100AU).
2013-12-31