Abstract
Carlisle Lakes and Allan Hills 85151 (ALH85151) are members of a new grouplet of chondrites characterized by FeO-rich silicates (olivine Fa = 38–41 mol%), unusual oxygen isotopic composition, and abundant (∼35 vol%) recrystallized matrix material. Yamato 75302 is not as well-characterized, but is probably also a member of this grouplet. Siderophile elements in Carlisle Lakes and ALH85151 are fractionated relative to CI chondrites: refractory and common siderophiles are at ∼ 1 × CI, Ga and As are lower (0.6-0.9 × CI), and Au is very low (0.17 × CI and 0.36 × CI in Carlisle Lakes and ALH85151, respectively). The low Au abundance may indicate that Au resided mainly in fine-grained metal particles that were suspended in the nebular gas during the time these chondrites agglomerated. The oxidation state of chondrites may be controlled by the presence of oxidizing agents (e.g., magnetite) in agglomerated matrix material. The high matrix abundance that characterizes this new grouplet may thus be responsible for the high oxidation state of these meteorites.
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