XRD ANALYSIS OF MAFIC SANDS FROM THE ICELANDIC INTERIOR: AN ANALOGUE STUDY FOR THE BAGNOLD DUNE FIELD OF MARS

The remote Icelandic interior appears otherworldly--lava flows formed by the actively rifting Northern Volcanic Zone are carved by glacial rivers and scoured by sediments carried by katibatic winds. One of the few, and one of the best, examples of a mafic sand sheet on Earth originates at the margin of the Vatnajökull ice cap and extends northward into the Icelandic interior, containing material related to the Askja caldera system. This mafic sand sheet is an appropriate terrestrial analogue for the Bagnold Dunes of Mars. We are contributing to a planetary investigation of sediment provenance, transportation, and deposition by seeking patterns in crystalline content (XRD) between samples of sand collected at a variety of distances from the ice. Powder XRD analyses of bulk sand samples, conducted using 20-minute scans from 5° to 70° 2θ at 45 kV on a PANalytical Empyrean instrument, yield reproducible results. Samples analyzed twice at different orientations consistently reveal the same major mineral phases present (e.g., anorthite with diopside, albite with augite), in the same relative abundance (typically within +/- 5%), with the same Highscore Plus software spectra matching scores (typically within +/- 10%). Preliminary XRD results reveal general similarities in major mineral assemblages--unsurprising for a suite of mafic samples, even those collected at different locations within an aeolian sand sheet. Plagioclase feldspar tends to dominate the mineral assemblage within individual samples (~60-100%), with clinopyroxene emerging as the second-most common phase present (~20-40%). Despite these broad similarities, subtle, but perhaps significant, distinctions exist between samples. Powder XRD spectra most often—but not always—reveal mineral assemblages dominated by anorthite (~75% typical; 67-100% observed) coupled with diopside (~25% typical, 22-33% observed). In some cases, results reveal albite-dominated assemblages (~63%) coupled with augite (~ 37%). Observed differences between mineral phases present, or relative abundances, are suggestive of variability within the sand sheet and warrant further study in the form of more XRD analyses, GIS investigations of distribution, and compositional analysis (ICP-MS, EDS, PXRF) to supplement XRD characterization of powdered sands.