Comparing Analysis of Hydrogen Concentration in Astromaterials Nominally Anhydrous Minerals by Multiple SIMS

Secondary Ion Mass Spectrometry (SIMS) is utilized to determine hydrogen (H) concentration in
astromaterials nominally anhydrous minerals (NAMs) and their inclusions [e.g., 1]. This data is
interpreted to refine the volatile history of planetary bodies.

Four instruments are being used to compare H concentration analysis: a large geometry SIMS (The University of Hawaiʻi Cameca IMS 1280), a compact SIMS (Arizona State University (ASU) Cameca IMS 6f), and two Cameca NanoSIMS 50L at ASU and NASA-Johnson Space Center (JSC). Results on the first three instruments are available. Although fundamentally similar, SIMS instruments and their modifications [2] may produce different values or pose advantages for H analysis, especially for shocked samples that are susceptible to contamination filling their fractures.

New data from the IMS 1280 is reported, using its microchannel plate (MCP) to image high H signals in grain fractures during pre-sputtering to avoid them as much as possible. Between fractures, 16OH/30Si was measured with a Cs+ 4 nA primary beam, 30 micron spot size, and central ~5x5 micron collection area.

First order comparison of H concentration (reported in ppm H2O) is achieved on a terrestrial gem quality clinopyroxene (SLP114, 162±12 ppm H2O [3]), with 157±7 and 215±40 ppm H2O by the IMS 1280 and 6f respectively. SIMS comparison is then extended to analysis of two Martian shergottites: RBT 04262 and NWA 5789. Due to a dense fracture network (< 20 micron) in RBT 04262, only one clinopyroxene hosted glassy inclusion was analyzed (n=6, ≤1 ppm H2O), while six olivine grains in NWA 5789 (n=12, ≤ 2 ppm H2O) (1s ±0.21) were analyzed. Higher concentrations were obtained for RBT 04262 olivine by the ASU NanoSIMS 50L (up to 350 ppm H2O [4]), and IMS 6f (300+ ppm H2O, [5]), for which contamination in fractures could not be avoided. Work on the JSC NanoSIMS 50L will further develop the SIMS comparison.