Water contents of nominally anhydrous orthopyroxenes from oceanic peridotites determined by SIMS and FTIR

Abstract This study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al 2 O 3 ranges 4.02 5.56 wt%, Cr 0.21 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the of eleven vary dry to 249 ± 6 µg/g H O. Using these grains, a set orthopyroxene samples obtained variably altered abyssal peridotites Atlantic Arctic Ridges as well Izu-Bonin-Mariana forearc region was analyzed by SIMS FTIR regarding their incorporation water. major element composition sample is typical mantle, characterized 0.90 0.92, 1.66 5.34 0.62 0.96 Water measured range 68 7 261 11 correlate with (r = 0.80) Cr#s . -0.89). We also describe detail an optimized strategy, employing both FTIR, quantifying structural highly such peridotite. approach first analyzes individual oriented grains polarized which provides overview alteration. Subsequently, same grain along others using SIMS, thereby gaining information about homogeneity at hand scale, key understanding geological history rocks.