METEORITE FORENSICS: PETROLOGICAL AND GEOCHEMICAL CHARACTERIZATION OF LUNAR METEORITE DOMINION (DOM) RANGE 18666

The 2018-2019 Antarctic Search for Meteorites (ANSMET) returned 8 paired lunar basaltic regolith breccias from the Dominion Range (DOM) including DOM 18666 which is the focus of this study. DOM 18666 is characterized by a fine-grained, glassy matrix and a variably vesiculated fusion crust. Clasts (<10%) are dominantly basaltic (plag-pyx) with minor 3-phase symplectites (fayalite-hedenbergite-silica) and impact melt breccias. Mineral fragments are dominated by pyroxene and Ca-rich feldspars with minor olivine and rare oxides (ilmenite), sulfides (troilite) and phosphates (apatite). Volumetric mineralogy evaluated via XCT on a DOM 18666 chip is consistent with observations made via PLM and SEM-EDS on a 1-inch thin section round.

Fe (apfu) vs. Mn (apfu) systematics for pyroxenes and olivines (n=276) are consistent with lunar Mn/Fe ratios and with the lunar meteorite compositional field. Pyroxenes are dominantly augite and pigeonite: Wo_3-46En_1-74Fs_20-80 while approximately half of the matrix olivines analyzed are fayalitic at <Fo₁₀. The remaining scatter up to Fo₆₉. Feldspars are anorthitic (average An₉₄) over a restricted range: An_82-99Ab_0-16Or_0-2 (n=61). Oxides are primarily ilmenite (n=48) with minor ulvöspinel (n=13) and rare magnetite (n=1). Trace apatites are fluorapatites (n=3) and matrix glass spherules (n=28) are compositionally distinct from lunar volcanic glass beads supporting the inference that DOM 18666 is a regolith breccia.

Pyroxene Fe/(Fe+Mg) vs. Ti/(Ti+Cr) systematics are consistent with derivation from low-Ti basalts while lunar glass compositions are consistent with contributions from a feldspathic highlands source. While fayalitic olivine on the Moon is rare, similarly high Fa contents are reported for the YAMM suite of meteorites. Recently reported ²⁰⁶Pb/²⁰⁷Pb ages from apatite in DOM 18666 (and 18262) indicate crystallization ages from 3.86Ga to 3.96Ga, which are also similar to ages reported for the YAMM suite (Hayden et al. 2022).

It is tentatively inferred that the 2018-2019 DOM suite of lunar meteorites is derived from a low-Ti basaltic province with contributions from feldspathic highland materials delivered via impact, or from a nearby province.

Hayden et al. (2022). Mineralogy, Geochemistry, and Geochronology of Lunar Meteorites from the Dominion Range and their Pairing Relationships. LPSC #1894.