Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) with Raman Imaging Applied to Lunar Meteorites

• Published in: Applied Spectroscopy
• Main Authors: Smith, Joseph P., Smith, Frank C., Booksh, Karl S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2017
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1177/0003702817721715; http://journals.sagepub.com/doi/pdf/10.1177/0003702817721715; http://journals.sagepub.com/doi/full-xml/10.1177/0003702817721715

Lunar meteorites provide a more random sampling of the surface of the Moon than do the returned lunar samples, and they provide valuable information to help estimate the chemical composition of the lunar crust, the lunar mantle, and the bulk Moon. As of July 2014, ∼96 lunar meteorites had been documented and ten of these are unbrecciated mare basalts. Using Raman imaging with multivariate curve resolution–alternating least squares (MCR-ALS), we investigated portions of polished thin sections of paired, unbrecciated, mare-basalt lunar meteorites that had been collected from the LaPaz Icefield (LAP) of Antarctica—LAP 02205 and LAP 04841. Polarized light microscopy displays that both meteorites are heterogeneous and consist of polydispersed sized and shaped particles of varying chemical composition. For two distinct probed areas within each meteorite, the individual chemical species and associated chemical maps were elucidated using MCR-ALS applied to Raman hyperspectral images. For LAP 02205, spatially and spectrally resolved clinopyroxene, ilmenite, substrate-adhesive epoxy, and diamond polish were observed within the probed areas. Similarly, for LAP 04841, spatially resolved chemical images with corresponding resolved Raman spectra of clinopyroxene, troilite, a high-temperature polymorph of anorthite, substrate-adhesive epoxy, and diamond polish were generated. In both LAP 02205 and LAP 04841, substrate-adhesive epoxy and diamond polish were more readily observed within fractures/veinlet features. Spectrally diverse clinopyroxenes were resolved in LAP 04841. Factors that allow these resolved clinopyroxenes to be differentiated include crystal orientation, spatially distinct chemical zoning of pyroxene crystals, and/or chemical and molecular composition. The minerals identified using this analytical methodology—clinopyroxene, anorthite, ilmenite, and troilite—are consistent with the results of previous studies of the two meteorites using electron microprobe analysis. To our knowledge, this is the first report of ...