Non-destructive analyses of Martian meteorites using Raman Spectroscopy

English Abstract:

Raman spectroscopy is an important tool to study highly shocked extraterrestrial materials. It provides complementary measurements of the short-range order phenomena in solid matter to other microstructural techniques to unravel the complex petrogenic history of these rare samples. Spectroscopy is of particular utility in studying amorphous materials such as maskelynite, metamict minerals and melt glasses and can also detect structural changes due to shock and inclusions of volatile or glassy material. Raman spectroscopy is also ideal in identifying high pressure polymorphs (e.g. the SiO₂ polymorphs) and weathering products. Characterization of the minerals present, with particular attention to the regions where it forms aids in the interpretation of the P-T formation conditions of the rocks. This could help answer the question whether high pressure phases are due to local (small-scale) pressure spikes or larger-scale pressures experienced by the whole rock.

Some recent work on martian meteorites have demonstrated the importance of detailed mineralogical characterization in interpreting geochronological data. Using a HORIBA Jobin Yvon LabRAM ARAMIS integrated confocal micro-Raman system with three excitation wavelengths of 532, 633, 785 nm we have non-destructively characterized a chemically diverse suite of martian meteorites. Through the use of our automated mapping stage and autofocus we are able to create mineral maps of areas much larger than generally achievable with Raman instruments. These maps can then be used for modal measurements allowing primary phases, and secondary weathering phases, to be quantified. Of particular interest were U-bearing phases such as zircon, baddeleyite, apatite-group minerals and merrillite as targets for subsequent studies.