Primitive and differentiated achondrite meteorites and partial melting in the early Solar System

This study aims to reveal details in the processes by which planetary bodies differentiate by using meteorites as snapshots of partial melting, metal segregation, and recrystallization in the early Solar System. A sample suite of twenty-two undifferentiated chondrite, slightly melted primitive achondrite, and differentiated achondrite meteorites was collected and subjected to petrographic, electron microprobe, whole-rock trace- and major-element, and oxygen isotope analyses. Graphite in a single meteorite, MIL 091004, was subjected to Raman spectroscopy analysis. Because the sample set ranges between undifferentiated and fully differentiated, attempts to make links between different stages in petrologic processes can be attempted. Rare-earth and whole-rock siderophile element abundances can be used to establish basic behaviors in meteorites, especially in the primitive acapulcoites and lodranites. Acapulcoites have chondrite-like chemistries. In lodranites, chemical abundances help establish part of the group as metal cumulates, and others as having experienced metal loss. Recent finds MIL 090405 and MIL 090206 are likely brachinite-like achondrites, and MIL 090405 displays trace-element patterns complimentary to the felsic meteorites GRA 06128/9. The expanding compositional range of brachinite-like achondrites suggests that low degree partial melting was common on small planetesimals in the early Solar System. Petrologic diversity in LEW 88763 may reveal process-related links between meteorite groups. Its existence also points to diverse oxidation environments in the early Solar System. MIL 091004 is a ureilite that contains an intrusive region with an exceptional amount of graphite grains. The meteorite points to re-fertilization processes on the ureilite parent body.