Unique achondrite Northwest Africa 11042: Exploring the melting and breakup of the L Chondrite parent body

TL;DR

This study characterizes the unique achondrite NWA 11042, revealing its origin from the L chondrite parent body, its complex igneous history likely driven by impact events, and its potential pairing with NWA 4284.

Contribution

It provides detailed geochemical and isotopic analysis of NWA 11042, linking it to the L chondrite parent body and proposing its igneous history and possible pairing with NWA 4284.

Findings

NWA 11042 is a heavily shocked achondrite with L chondrite characteristics.

Crystallization age of 4100 Ma and shock age of 484 Ma suggest impact-related history.

Depletion in siderophile elements indicates complex igneous processes.

Abstract

Northwest Africa (NWA) 11042 is a heavily shocked achondrite with medium-grained cumulate textures. Its olivine and pyroxene compositions, oxygen isotopic composition, and chromium isotopic composition are consistent with L chondrites. Sm-Nd dating of its primary phases shows a crystallization age of 4100 +/- 160 Ma. Ar-Ar dating of its shocked mineral maskelynite reveals an age of 484.0 +/- 1.5 Ma. This age coincides roughly with the breakup event of the L chondrite parent body evident in the shock ages of many L chondrites and the terrestrial record of fossil L chondritic chromite. NWA 11042 shows large depletions in siderophile elements (<0.01 times CI) suggestive of a complex igneous history involving extraction of a Fe-Ni-S liquid on the L chondrite parent body. Due to its relatively young crystallization age, the heat source for such an igneous process is most likely impact. Because its mineralogy, petrology, and O isotopes are similar to the ungrouped achondrite NWA 4284 (this work), the two meteorites are likely paired and derived from the same parent body.