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Quantification of Water in Hydrous Ringwoodite

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ORIGINAL RESEARCH ARTICLE published: 28 January 2015 EARTH SCIENCE doi: 10.3389/feart.2014.00038 Quantification of water in hydrous ringwoodite Sylvia-Monique Thomas 1*,StevenD.Jacobsen2, Craig R. Bina 2, Patrick Reichart 3, Marcus Moser 3, Erik H. Hauri 4, Monika Koch-Müller 5,JosephR.Smyth6 and Günther Dollinger 3 1 Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV, USA 2 Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, USA 3 Department für Luft- und Raumfahrttechnik LRT2, Universität der Bundeswehr München, Neubiberg, Germany 4 Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, USA 5 Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum (GFZ), Potsdam, Germany 6 Department of Geological Sciences, University of Colorado Boulder, Boulder, CO, USA Edited by: Ringwoodite, γ-(Mg,Fe)2SiO4, in the lower 150 km of Earth’s mantle transition zone Mainak Mookherjee, Cornell (410–660 km depth) can incorporate up to 1.5–2wt% H2O as hydroxyl defects. We University, USA present a mineral-specific IR calibration for the absolute water content in hydrous Reviewed by: ringwoodite by combining results from Raman spectroscopy, secondary ion mass Geoffrey David Bromiley, University of Edinburgh, UK spectrometry (SIMS) and proton-proton (pp)-scattering on a suite of synthetic Mg- and Marc Blanchard, CNRS - Université Fe-bearing hydrous ringwoodites. H2O concentrations in the crystals studied here Pierre et Marie Curie, France range from 0.46 to 1.7wt% H2O (absolute methods), with the maximum H2Oin *Correspondence: the same sample giving 2.5 wt% by SIMS calibration. Anchoring our spectroscopic Sylvia-Monique Thomas, results to absolute H-atom concentrations from pp-scattering measurements, we report Department of Geoscience, University of Nevada Las Vegas, frequency-dependent integrated IR-absorption coefficients for water in ringwoodite −1 −2 4505 S. Maryland Parkway, LFG 114, ranging from 78,180 to 158,880 Lmol cm , depending upon frequency of the OH Las Vegas NV 89154-4010, USA absorption. We further report a linear wavenumber IR calibration for H2O quantification in e-mail: sylvia-monique.thomas@ hydrous ringwoodite across the Mg SiO -Fe SiO solid solution, which will lead to more unlv.edu 2 4 2 4 accurate estimations of the water content in both laboratory-grown and naturally occurring ringwoodites. Re-evaluation of the IR spectrum for a natural hydrous ringwoodite inclusion in diamond from the study of Pearson et al. (2014) indicates the crystal contains 1.43 ± 0.27 wt% H2O, thus confirming near-maximum amounts of H2O for this sample from the transition zone. Keywords: IR spectroscopy, water in nominally anhydrous minerals, transition zone, mineral-specific absorption coefficient, SIMS, Raman spectroscopy, proton-proton scattering, ringwoodite INTRODUCTION in ringwoodite, mainly involving charge-compensating vacancies Ringwoodite was first described in the Tenham meteorite found at the octahedral Mg-Fe sites, the tetrahedral Si site, and normally in Queensland, Australia, by Binns et al. (1969) and named after vacant interstitial sites (e.g., Kudoh et al., 2000; Smyth et al., 2003, the Australian mineral physicist Ted Ringwood. The first terres- 2004; Chamorro Pérez et al., 2006; Blanchard et al., 2009; Mrosko trial occurrence of ringwoodite was recently reported by Pearson et al., 2013; Panero et al., 2013; Purevjav et al., 2014; Yang et al., et al. (2014), who discovered a hydrous ringwoodite inclusion in 2014). ultra-deep diamonds from Juina, Brazil. Ringwoodite is one of Because of its likely abundance (>50% of a pyrolite model) themajorcomponentsoftheEarth’smantletransitionzone(e.g., in the lower 150 km of the Earth’s mantle transition zone Bernal, 1936; Akaogi and Akimoto, 1977; Anderson and Bass, (410–660 km depth) and for its ability to incorporate significant 1986; Bina and Wood, 1986; Irifune, 1987; Ringwood and Major, amounts of H2O, we have undertaken this study on determining 1967) and although nominally anhydrous, ringwoodite is well- the absolute water content in ringwoodite. Infrared (IR) spec- known to incorporate up to 1.5–2 wt% of water as (OH)− point troscopy is one of the most common tools for analysis of water in defects in both laboratory-grown and naturally occurring samples minerals, for which mineral-specific absorption coefficients are (e.g., Kohlstedt et al., 1996; Bolfan-Casanova et al., 2000; Smyth required. The absolute water content in minerals was conven- et al., 2003; Pearson et al., 2014). tionally determined by quantitative dehydration weight analyses Water in nominally anhydrous minerals (NAMs) influences (e.g., Aines and Rossman, 1984), but more suitable for the typ- phase relations (e.g., Hirschmann, 2006), melting temperature ically very small amounts (μg) of material from high-pressure (e.g., Hirth and Kohlstedt, 1996; Hirschmann et al., 2009; Tenner and high-temperature syntheses, two additional methods have et al., 2012), and physical properties including electrical conduc- been developed: elastic recoil detection analysis (e.g., Aubaud tivity (e.g., Yoshino et al., 2009), thermal conductivity (Thomas et al., 2009; Bureau et al., 2009; Withers et al., 2012)andproton- et al., 2012), elasticity (e.g., Jacobsen, 2006), and rheology (e.g., proton (pp) scattering (e.g., Gose et al., 2008; Thomas et al., 2008; Kavner, 2003). Several OH defect mechanisms have been studied Reichart and Dollinger, 2009). www.frontiersin.org January 2015 | Volume 2 | Article 38 | 1 Thomas et al. Water in ringwoodite In addition to theoretically based IR calibrations for water in ringwoodite (Balan et al., 2008; Blanchard et al., 2009), % % % experimentally determined IR absorption coefficients have been % 0.30 0.06 0.30 0.06 0.01 0.03 0.02 estimated for ringwoodite either by using general calibrations 0.02 ± ± ± ± ± ± ± (Paterson, 1982; Libowitzky and Rossman, 1997)orfromsec- ± ondary ion mass spectrometry (SIMS) measurements of water contents, which we note are usually calibrated against the water content in silicate glasses or minerals measured by IR. Absorption coefficients for water quantification have been determined for ringwoodites with fayalite component (Fa100, Fe2SiO4)through Fa40 and for pure forsterite (Fo100, Mg2SiO4) composition (Koch-Müller and Rhede, 2010) but not for compositions span- 0.140.12 0.89 0.36 0.07 1.11 0.51 2.50 ning the likely Fe-content of the mantle transition zone from Fo75 0.30 1.38 ± ± ± ± to Fo95. ± In this study we calibrate the water concentrations in synthetic hydrous ringwoodite from IR spectroscopy against independently determined values from Raman spectroscopy, SIMS and the absorption coefficient. absolute H-concentration measured by pp-scattering microscopy. Broad-beam pp-scattering has previously been applied to mm- sized samples (Thomas et al., 2008). However, until recently this quantification technique was not feasible for smaller samples syn- 0.18 1.16 0.35 1.65 thesized under very high pressure-temperature conditions in the 0.23 0.85 ± ± multi-anvil press. Here, we employ pp-scattering experiments on ± synthetic ringwoodite crystals less than 200 μm in largest dimen- sion and quantify 3D distributions of atomic hydrogen at μm spatial resolution. We also present hydrogen depth-profiles and 2D hydrogen maps and H2O concentrations in samples used for ) Independent determined Independent determined Independent determined the spectroscopic calibration. We calculate absorption coefficients 2 − for a suite of hydrous ringwoodite with varying Fe- and water (cm concentrations, test their wavenumber-dependence, and compare i results with literature data. The IR calibration can thus be used ) PP-scattering (wt%) Raman spectroscopy (wt%) SIMS (wt%) to determine the absolute water content in hydrous ringwoodite, 1 − m for SZ0820, respectively. which we also apply to the natural hydrous ringwoodite inclusion μ in diamond reported by Pearson et al. (2014). MATERIALS AND METHODS . )(cm 1 SAMPLES − Samples used in this study were synthesized at high P-T condi- O analyses. 2 m for SZ0570 and 50 tions in multi-anvil presses and cover a range of H2Ocontents μ and compositions (Table 1). Chemical analyses and other char- )(cm acterizationsofthesinglecrystalsusedinthisstudyhavebeen 3 published elsewhere: for samples MA120, MA62, MA56, and (cm MA75, see Koch-Müller and Rhede (2010), Taran et al. (2009), Koch-Müller and Rhede (2010) ) volume wavenumber maximum water content from water content from water content from and Koch-Müller et al. (2009); Koch-Müller et al. (2011); for sam- 3 ple SZ0820, see Ye et al. (2012); for samples SZ9901 and SZ0104, see Smyth et al. (2003); Smyth et al. (2004), Thomas et al. (2012), and Jacobsen et al. (2004); for sample SZ0570, see Mao et al. (2011). High-quality, crack- and inclusion-free isotropic single * μ m) crystals ranging in longest dimension from 50 to 500 mwere µ ( selected for analyses. The color of the ringwoodites used here thickness (g/cm varies from colorless to dark blue to almost opaque depending on Fe concentration. Fo60Fo39Fo22Fay – – – 4.09 – 4.36 40.52 4.56 41.11 4.87 41.65 3220 42.14 3240 3320 3244 3400 3260 3358 81,720 56,820 3386 31,440 32,000 – – – – 0.46 – – – 0.30 0.19 0.21 3D HYDROGEN MICROSCOPY BY PROTON-PROTON SCATTERING Proton-proton scattering at proton energies up to 25 MeV has % % % % been used in a broad-beam configuration to perform hydrogen Sample characterization and water content from Thicknesses of samples used for pp-scattering analyses were 71 Table 1 | Sample information and IR spectroscopic data for H Run no. Run info SampleSZ0820 DensitySZ9901 Fo100 MolarSZ0104 Fo90SZ0570 Fo87 Mean 84 Fo83MA62 39MA56 13 3.47MA75 Band 18 3.65Note that 40.55 we A use one-directional% 3.67 absorbance values derived from unpolarized spectra 40.27 3.73 of* cubic ringwoodite and multiply them 40.57 by 3232 three to calculate the 40.59 3240 3273 3130 3240 3168 361,800 3169 188,500 3174 304,500 1.77 234,900 1.13 0.91 – 0.94 depth microscopy in mm-sized mineral platelets, as described MA120 Frontiers in Earth Science | Earth and Planetary Materials January 2015 | Volume 2 | Article 38 | 2 Thomas et al.
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