Lidia Pittarello¹, Kitty Baert², Vinciane Debaille³ and Philippe Claeys^1
1Earth System Science, Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Brussels, Belgium
²Materials and Chemistry, Research Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel, Brussels, Belgium
³Laboratoire G-Time, Geochemistry: Tracing with isotopes, minerals and elements, Université Libre de Bruxelles, Brussels, Belgium

Classification of ordinary chondrite meteorites generally implies (1) determining the chemical group by the composition in endmembers of olivine and pyroxene, and (2) identifying the petrologic group by microstructural features. The composition of olivine and pyroxene is commonly obtained by microprobe analyses or oil immersion of mineral separates. We propose Raman spectroscopy as an alternative technique to determine the endmember content of olivine and pyroxene in ordinary chondrites, by using the link between the wavelength shift of selected characteristic peaks in the spectra of olivine and pyroxene and the Mg/Fe ratio in these phases. The existing correlation curve has been recalculated from the Raman spectrum of reference minerals of known composition and further refined for the range of chondritic compositions. Although the technique is not as accurate as the microprobe for determining the composition of olivine and pyroxene, for most of the samples the chemical group can be easily determined by Raman spectroscopy. Blind tests with ordinary chondrites of different provenance, weathering, and shock stages have confirmed the potential of the method. Therefore, we suggest that a preliminary screening and the classification of most of the equilibrated ordinary chondrites can be carried out using an optical microscope equipped with a Raman spectrometer.

Reference
Pittarello L, Baert K, Debaille V and Claeys P (2015) Screening and classification of ordinary chondrites by Raman spectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [http://onlinelibrary.wiley.com/doi/10.1111/maps.12506/abstract]
Published by arrangement with John Wiley & Sons

B.A. Wing^a,b,c, J. Farquhar^c
aDepartment of Earth and Planetary Sciences, McGill University, Montreal QC H3A 2A7 CANADA
^bGEOTOP Research Center, C.P. 8888, Succursale Centre-ville, Montréal, QC H3C 3P8, CANADA
^cEarth System Science Interdisciplinary Center and Department of Geology, University of Maryland, College Park MD 20742 USA

We present a new set of high precision measurements of relative ³³S/³²S, ³⁴S/³²S, and ³⁶S/³²S values in lunar mare basalts. The measurements are referenced to the Vienna-Canyon Diablo Troilite (V-CDT) scale, on which the international reference material, IAEA-S-1, is characterized by δ³³S = -0.061 ‰, δ³⁴S ≡ -0.3 ‰ and δ36S = -1.27 ‰. The present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity, with most new and published SF6-based sulfur isotope measurements consistent with a single mass-dependent mean isotopic composition of δ³⁴S = 0.58 ± 0.05 ‰, Δ³³S = 0.008 ± 0.006 ‰, and Δ³⁶S = 0.2 ± 0.2 ‰, relative to V-CDT, where the uncertainties are quoted as 99% confidence intervals on the mean. This homogeneity allows identification of a single sample (12022, 281) with an apparent ³³S enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower δ³⁴S values than the population mean, which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface. Both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization-driven fractionation suggest that less than ≈1-10% of lunar sulfur was lost after a potential moon-forming impact event.

Reference
Wing BA, Farquhar J (2015) Sulfur isotope homogeneity of lunar mare basalts. Geochimica et Cosmochimica Acta (in Press)
Link to Article [ http://www.sciencedirect.com/science/article/pii/S0016703715005323]
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