Sulfur isotope homogeneity of lunar mare basalts

We present a new set of high precision measurements of relative S-33/S-32, S-34/S-32, and S-36/S-32 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 delta S-33 = -0.061%, delta S-34 = -0.3% and delta S-36 = -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 delta S-34 = 0.58 +/- 0.05%, Delta S-33 = 0.008 +/- 0.006%, and Delta S-36 = 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 S-33 enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower d34S 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 approximate to 1-10% of lunar sulfur was lost after a potential moon-forming impact event. (C) 2015 Elsevier Ltd. All rights reserved.