Solubility and partitioning of water in synthetic forsterite and enstatite in the system MgO–SiO2–H2O±Al2O3
Tóm tắt
The solubility of water in coexisting enstatite and forsterite was investigated by simultaneously synthesizing the two phases in a series of high pressure and temperature piston cylinder experiments. Experiments were performed at 1.0 and 2.0 GPa at temperatures between 1,100 and 1,420°C. Integrated OH absorbances were determined using polarized infrared spectroscopy on orientated single crystals of each phase. Phase water contents were estimated using the calibration of Libowitzky and Rossman (Am Mineral 82:1111–1115, 1997). Enstatite crystals, synthesized in equilibrium with forsterite and an aqueous phase at 1,350°C and 2.0 GPa, contain 114 ppm H2O. This is reduced to 59 ppm at 1,100°C, under otherwise identical conditions, suggesting a strong temperature dependence. At 1,350°C and 1.0 GPa water solubility in enstatite is 89 ppm, significantly lower than that at 2.0 GPa. In contrast water solubility in forsterite is essentially constant, being in the range 36–41 ppm for all conditions studied. These data give partition coefficients
$$ {\text{D}}_{{{\text{H}}_{2} {\text{O}}}} ^{{{\text{en}}/{\text{fo}}}} $$
in the range 2.28–3.31 for all experiments at 1,350°C and 1.34 for one experiment at 1,100°C. The incorporation of Al2O3 in enstatite modifies the OH stretching spectrum in a systematic way, and slightly increases the water solubility.
Tài liệu tham khảo
Aubaud C, Hauri EH, Hirschmann MM (2004) Water partition coefficients between nominally anhydrous minerals and basaltic melts. J Geophys Res 31:L20611 DOI: 20610.21029/22004GL021341
Bai Q, Kohlstedt DL (1993) Effects of chemical environment on the solubility and incorporation mechanism for hydrogen in olivine. Phys Chem Miner 19:460–471
Bell DR, Ihinger PD, Rossman GR (1995) Quantitative analysis of trace OH in garnet and pyroxenes. Am Mineral 80:465–474
Bell DR, Rossman GR, Maldener J, Endisch D, Rauch F (2003) Hydroxide in olivine: a quantitative determination of the absolute amount and calibration of the IR spectrum. J Geophys Res 108(B2):2105
Bell DR, Rossman GR, Moore RO (2004) Abundance and partitioning of OH in a high pressure magmatic system: megacrysts from the Monastery Kimberlite, South Africa. J Petrol 45(8):1539–1564
Berry AJ, Hermann J, O’Neill H, St.C., Foran GJ (2005) The incorporation of water in mantle olivine. Geology 33(11):869–872
Braithwaite JS, Wright KV, Catlow CRA (2003) A theoretical study of the energetics and IR frequencies of hydroxyl defects in forsterite. J Geophys Res 108(B6):1–9
Brodholt JP (1997) Ab initio calculations on point defects in forsterite (Mg2SiO4) and implications for diffusion and creep. Am Mineral 82:1049–1053
Dobson PF, Skogby H, Rossman GR (1995) Water in bonninite glass and coexisting orthopyroxene: concentration and partitioning. Contrib Mineral Petrol 118:414–419
Grant KJ, Kohn SC, Brooker RA (2004) Hydrogen partitioning between synthetic olivine, orthopyroxene and melt. Geochim Cosmochim Acta 68:A34
Hirth G, Kohlstedt DL (1996) Water in the oceanic upper mantle: implications for rheology, melt extraction and the evolution of the lithosphere. Earth Planet Sci Lett 144:93–108
Ingrin J, Skogby H (2000) Hydrogen in nominally anhydrous upper-mantle minerals: concentration levels and implications. Eur J Mineral 12:543–570
Inoue T (1994) Effect of water on melting phase relations and melt composition in the system Mg2SiO4-MgSiO3-H2O up to 15 GPa. Phys Earth Planet Inter 85:237–263
Koga K, Hauri E, Hirschmann M, Bell DR (2003) Hydrogen concentration analyses using SIMS and FTIR: comparison and calibration for nominally anhydrous minerals. Geochem Geophys Geosyst 4(2):1019 DOI:1010.1029/2002GC00378
Kohlstedt DL, Keppler H, Rubie DC (1996) Solubility of water in the α-phase, β-phase and γ-phase of (Mg,Fe)2SiO4. Contrib Mineral Petrol 123:345–357
Kohn SC (1996) Solubility of H2O in nominally anhydrous mantle minerals using 1H MAS NMR. Am Mineral 81:1523–1526
Lemaire C, Kohn SC, Brooker RA (2004) The effect of silica activity on the incorporation mechanisms of water in synthetic forsterite: a polarised infrared spectroscopic study. Contrib Mineral Petrol 147:48–57
Libowitzky E, Beran A (2004) IR spectroscopic characterisation of hydrous species in minerals. In: Beran A, Libowitzky E (eds) Spectroscopic methods in mineralogy, vol. 6. European Mineralogical Union, Budapest, pp 227–279
Libowitzky E, Rossman GR (1997) An IR absorption calibration for water in minerals. Am Mineral 82:1111–1115
Mackwell SJ, Kohlstedt DL (1990) Diffusion of hydrogen in olivine: implications for water in the mantle. J Geophys Res 95:11319–11333
Matveev S, O’Neill H, ST C, Ballhaus C, Taylor WR, Green DH (2001) Effect of silica activity on OH- IR spectra of olivine: Implications for low-αSiO2 mantle metasomatism. J Petrol 42(4):721–729
Matveev S, Portnyagin M, Ballhaus C, Brooker RA, Geiger CA (2005) FTIR spectrum of phenocryst olivine as an indicator of silica saturation in magmas. J Petrol 46(3):603–614
McDade P, Wood B, Van Westrenen WBR, Gudmundsson G, Soulard H, Najorka J, Blundy J (2002) Pressure corrections for a selection of piston-cylinder assembles. Mineral Mag 66:1021–1028
Mierdel K, Keppler H (2004) The temperature dependence of water solubility in enstatite. Contrib Mineral Petrol 148(3):305–311
Paterson MS (1982) The determination of hydroxyl by infrared absorption in quartz, silicate glasses and similar materials. Bull Minérallogie 105:20–29
Peslier AH, Luhr JF, Post J (2002) Low water contents in pyroxenes from spinel-peridotites of the oxidized, sub-arc mantle wedge. Earth Planet Sci Lett 201:69–86
Rauch M, Keppler H (2002) Water solubility in orthopyroxene. Contrib Mineral Petrol 143:525–536
Stalder R (2004) Influence of Fe, Cr and Al on hydrogen incorporation in orthopyroxene. Eur J Mineral 16:703–711
Stalder R, Skogby H (2002) Hydrogen incorporation in enstatite. Eur J Mineral 14:1139–1144