分化した隕石の化学的・年代学的研究(1992年度日本地球化学会奨励賞受賞記念)

概要

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Diogenite and eucrite have been regarded as igneous products in the early solar system and they have been considered to correspond to a crust layer (eucrite) and a mantle layer (diogenite) of their parental body. These achondrites give informations concerning the early evolution history of planets or planetesimals. For two diogenites (Tatahouine and Johnstown), a Rb-Sr age of 4.39±0.01 b.y. younger than eucrites has been obtained, while most of typocal eucrites show the age of 4.5-4.5 b.y. Low initial ^<87>Sr/^<86>Sr value of 0.69896, and the characteristics of REE (rare earth element) abundance patterns observed for these two diogenites are inconsistent with an interpretation that the ages of these diogenites reflect secondary metamorphism(e.g. shock). These results do not support an idea of the genetically close relationship between eucrite and these diogenites and that there exist some groups of diogenitic achondrites genetically distinguished from each other. Our results suggest that the igneous activity in their assumed "parent body" would have continued for about hundred (130) million years after its formation 4.52 b.y. It is conceivable that their parent body had complicated evolution history.
日本地球化学会の論文
1994-03-24