Chemical composition of the Howardite parent body deduced from Kapoeta primary ‘mafic’ magmas

Abstract

Chemical data are presented for three ‘mafic’ clasts extracted from the Kapoeta howardite. Bulk compositions and petrologic observations suggest that two of these lithic clasts represent olivine‐plagioclase bearing orthopyroxenites. Chondrite‐relative refractory LIL abundances of two of the clasts are inferred to represent primary Mg‐rich magmas produced by extensive (≲ 70%) partial melting of a source composition indistinguishable from the silicate fraction of average CH‐CL ordinary chondrites, with the exception of the depletion of the alkalis Na and K by a factor of 13±1 in the source composition. A metal‐free and volatile depleted Kapoeta Parent Body (KPB) is subsequently deduced and is shown to compare very well with other similarly derived Achondrite Parent Body (APB) and Howardite Parent Body (HPB) estimates but not to parent body estimates derived from inferences based on eucrite phase equilibrium studies. Other implications suggest that the KPB is heterogeneous with respect to Fe/Mg ratios.