North-Central Section - 57th Annual Meeting - 2023

Paper No. 33-2
Presentation Time: 1:30 PM-5:30 PM


MCLEOD, Claire1, SCHWEITZER, Alex1, GAWRONSKA, Aleksandra1, BRUM, Jared1, LOOCKE, Matthew2 and SHAULIS, Barry J.3, (1)Department of Geology and Environmental Earth Science, Miami University, 118 Shideler Hall, Oxford, OH 45056, (2)Department of Geology and Geophysics, Louisiana State University, E 235 Howe-Russell-Kniffen, Baton Rouge, LA 70803, (3)University of Arkansas Trace element and Radiogenic Isotope Laboratory, University of Arkansas, Fayetteville, AR 72701

Lunar meteorites represent a random sampling of the lunar surface and therefore have the potential to significantly expand our understanding of the Moon’s history. This work focuses on the textural, mineralogical, and geochemical analysis of two of the most recently identified lunar meteorites: Dominion Range (DOM) 18666 and 18543.

Samples DOM 18666 and 18543 were returned during the 2018-2019 United States Antarctic Search for Meteorite (ANSMET). They are basaltic breccias characterized by a glassy, variably vesiculated fusion crust and a glassy fine grained matrix (~40-60%). The fine grained matrices are characterized by a range of subhedral to anhedral mineral fragments including Ca-rich plagioclase, pyroxene, and olivine, along with minor to trace oxides, sulfides, and phosphates. Glass spherules are also present and more abundant in 18543. Clast types identified include basalts, gabbros, impact melt breccias, and 3-phase symplectites.

Major phases (plagioclase, pyroxene, olivine) were analyzed for their major element abundances via EPMA. Fe-Mn systematics in pyroxene and olivine confirm a lunar origin for DOM 18666 and 18543. For olivine (n=84) Fe a.p.f.u ranges from 0.61 to 1.94 at corresponding Mn a.p.f.u from 0.006 to 0.029. For pyroxene (n=364), Fe a.p.f.u ranges from 0.11 to 1.91 at corresponding Mn a.p.f.u from 0.001 to 0.028. Clast and matrix plagioclase compositions are predominantly anorthite (≥An90). Clast and matrix pyroxenes range from augite to pigeonite while olivines are Fe-rich (up to Fa99). Apatite compositions in DOM 18666 are consistent with derivation from a melt with chlorine > H2O > fluorine. Pyroxene Fe/(Fe+Mg) vs. Ti/(Ti+Cr) systematics broadly overlap those low-Ti Apollo 15 basalt pyroxenes while the high Fa contents of olivine are similar to those in select YAMM group meteorites. Ongoing work will use the mineralogical and geochemical features of these meteorites to place constraints on their origin on the lunar surface.