Raman spectroscopy investigations of the Martian regolith breccia Northwest Africa 7533: A support to in situ Raman spectroscopy on Mars

Using continuous-wave and time-resolved Raman spectroscopy, we investigate and characterize the mineralogy of the NWA 7533 meteorite, a unique Martian regolith breccia. This meteorite is a crucial sample, giving a rare access to the formation and evolution of the primitive Martian crust, with crystallization processes beginning up to similar to 4.4 Ga years ago. We provide an overview of Raman spectra for feldspar, plagioclase, pyroxene, olivine, apatite, merrillite, zircon, pyrite, and various Fe-Cr-Ti oxides like magnetite, hematite, ilmenite, and rutile. Most analytical points are paired with previous electron microprobe analyses for deeper interpretation of Raman data. The variability of the silicate minerals composition obtained through microanalysis is traced through variation of the Raman spectra characteristics. No trace of any shock event is observed in the mineral structures. Structural diversity of zircon is linked to various metamictization stages. The luminescence signal of minerals bearing rare earth elements (REE), mainly phosphate and zircon, is documented in detail and discussed. We discuss the presence of at least two generations of phosphate minerals with implications for magmatic petrology. Because NWA 7533 provides a unique sampling of various crustal lithologies of Mars, this spectral dataset could be a reference for Raman instruments presently working on Mars (e.g., NASA Mars2020 Perseverance) or going to this planet or its moon Phobos in the future (e.g., ESA ExoMars, JAXA MMX).

Automated summary

Using Raman spectroscopy, the mineralogy of the NWA 7533 meteorite, a Martian regolith breccia, is investigated and characterized. This meteorite provides valuable insights into the formation and evolution of the primitive Martian crust. The Raman spectra of various minerals are analyzed, and the variability of silicate mineral composition is traced through microanalysis. The presence of luminescent minerals bearing rare earth elements is documented and discussed, with implications for magmatic petrology. This spectral dataset can serve as a reference for future Raman instruments exploring Mars or its moon Phobos.