GSA Connects 2024 Meeting in Anaheim, California

Paper No. 264-2
Presentation Time: 8:00 AM-5:30 PM

UNDERSTANDING LUNAR SPINEL PETROGENESIS THROUGH TEXTURAL AND CHEMICAL ANALYSIS OF SPINELS AND ASSOCIATED CLASTS OF LUNAR FRAGMENTAL BRECCIA NORTHWEST AFRICA 14577


DESOTO, Emily, Geology and Geophysics, Louisiana State University, E235 Howe Russell Kniffen, Baton Rouge, LA 70803

Northwest Africa (NWA) 14577 is a lunar fragmental breccia meteorite with an abundance of magnesium aluminate spinel also called pink spinel and Cr-spinel. Much of our current understanding of the lithologic occurrence of pink spinel on the Moon is limited to near-infrared spectra of the lunar surface and a few meteorites. It is suggested that the primary occurrence of pink spinel on the Moon is within pink spinel anorthosite (PSA). Chemical data of NWA 14577 was collected using the JEOL JXA-8230 electron microprobe in the Chevron Geomaterials Characterization Lab at LSU. Comparing the Fe# and Cr# of spinels found in this meteorite to other lunar lithologies shows that the spinels plot similarly to those from PSA and more Cr-rich compositions associated with mare basalts. We note that several spinel grains in NWA 14577 exhibit compositional zoning in Mg# and/or Cr# and a decrease in spinel Cr# and increase in Mg# is observed with increasing pyroxene abundance. A melt-rock reaction or metasomatic origin of the spinels and associated clasts in the lunar meteorite can be inferred based on the observations of a correlation between the compositional zoning in spinel and pyroxene abundance. Using images of NWA 14577 with various filters and chemical data from the electron microprobe, seven distinct groups of clasts were defined by their textural and chemical similarity. Each clast was outlined, and different colors were chosen to represent each clast group. The white group is defined by clasts that are 125-500 µm with alternating lines of white and gray. The dark green group is defined by a speckled texture with a wide range in size from 70-5750 µm. Of the 73 identified spinels in this meteorite, 25 were within clasts with the remaining as solitary crystals found in the matrix. Most of the spinels found in defined clasts correspond to the dark green group with no spinels found in the white or light green groups. Understanding the different textures and chemistries of the spinels and associated clasts found in NWA 14577 can aid us to better understand lunar spinel petrogenesis.