Abstract
The Y‐7308 howardite comprises a variety of lithic clasts and mineral fragments. The Mg/(Mg+Fe) atomic ratios of the pyroxenes in diogenitic clasts, eucritic clasts, and Fayalite‐Hedenbergite‐Tridymite‐Plagioclase clasts vary continuously from 0.76 to less than 0.30. Olivine fragments in the matrix have a wide range of Mg/(Mg+Fe) ratios from 0.88 to 0.71. This continuum of chemical compositions for olivine and pyroxene is explained by the fractional crystallization of a primary magma. The composition of a liquid produced by removing olivine and pyroxene from the primary magma is almost identical to that of eucrites, and the solidification of this liquid on the surface of a magma ocean might have formed a eucrite crust on the parent body. A source material of carbonaceous or LL chondrite‐like composition may produce the HED (Howardites, Eucrites, Diogenites) magma by partial or batch melting. The volatile components such as alkalis, sulfur oxides, etc. may have been lost, and reduction of FeO and Fe203 components to Fe metals also may have taken place prior to and/or during the formation and crystallization of the HED magma.
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