The variation of Zn content in spinel group minerals and daubreelites of primitive achondrites

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We have studied the Zn content of spinel group mineral and daubreelite in primitive achondrites in order to clarify how the content of Zn, a moderately volatile element, reflects their formation process. Primitive achondrites have achondritic texture and chondrite-related chemistry and mineralogy. Because of these characteristics, primitive achondrites are thought to represent the transition from chondrites to achondrites. We have compared the Zn content in spinel group minerals of primitive achondrites with those of chondrites and ureilites. Although Zn is a moderately volatile element, the Zn content in spinel group mineral of primitive achondrites, ureilites and metamorphosed chondrites is higher than unmetamorphosed chondrites. This fact suggests that high Zn content in spinel group mineral of primitive achondrites may result from secondary crystallization or reequilibration of spinel mineral from a sulfide melt containing Cr, Mn and Zn which was partially melted during thermal metamorphism. We also found that the Zn content in spinel group minerals decreases from primitive achondrites and ureilites to HED and Martian meteorites. We suggest that Zn was significantly volatilized from completely molten magma in these meteorites. We found that spinel group minerals and daubreelites appear to be the major reservoir of Zn in most meteorites. Zn may be preferentially retained in the tight spinel structure.
国立極地研究所の論文