Breakdown of hydrous ringwoodite to pyroxene and spinelloid at high P and T and oxidizing conditions

Abstract

From the Rietveld refinement we identified spl as spinelloid III (isostructural with wadsleyite) and/or spinelloid V. As we used water in excess in the experiments the run products were also analyzed for structural water incorporation. Adding Mg to the system increases the stability field of ringwoodite to higher oxygen fugacity and the spinel structure seems to accept higher Fe 3+ but also water concentrations that may be linked. At oxygen fugacity corresponding to MtW conditions similar phase relations in respect to the breakdown reaction in the Fe-end-member system were observed but with a strong fractionation of Fe into spl and Mg into coexisting cpx. Thus, through this strong fractionation it is possible to stabilize very Fe-rich wadsleyite with phase at P-T conditions of the transition zone but because of the oxidizing conditions and the Fe-rich bulk composition needed one would expect it more in subduction zone environments than in the transition zone in senso stricto.

IR absorption coefficients for water in nominally anhydrous high-pressure minerals

“…In all samples, water was added in excess and was still present after quenching. Infrared spectra in the OH-stretching range of the four synthetic ringwoodite samples are shown in Koch-Müller et al (2009) 2 . The ε-values of the four different ringwoodite samples plot well below the general calibration curve of Libowitzky and Rossman (1997) but follow the same trend, i.e., they increase with decreasing wavenumber of the OH bands (Fig.…”

“…For quantitative chemical analyses, the samples were embedded in a minimum amount of epoxy resin, polished, and analyzed using a JEOL thermal field emission type electron-probe JXA-8500F (HYPERPROBE). Details regarding the syntheses and microprobe analyses are given in Koch-Müller et al (2009). The crystal size decreases with increasing Mg content from about 500 µm for the Fe end-member, which appears opaque, to about 30 µm or less for the most Mg-richest sample (X Mg = 0.60), which shows a blue color (see Taran et al 2009).…”

Quantification of water in hydrous ringwoodite

“…Samples used in this study were synthesized at high P-T conditions in multi-anvil presses and cover a range of H 2 O contents and compositions (Table 1). Chemical analyses and other characterizations of the single crystals used in this study have been published elsewhere: for samples MA120, MA62, MA56, and MA75, see Koch-Müller and Rhede (2010), Taran et al (2009), and Koch-Müller et al (2009); Koch-Müller et al (2011); for sample SZ0820, see Ye et al (2012); for samples SZ9901 and SZ0104, see Smyth et al (2003); Smyth et al (2004), Thomas et al (2012), ; for sample SZ0570, see Mao et al (2011). High-quality, crack-and inclusion-free isotropic single crystals ranging in longest dimension from 50 to 500 μm were selected for analyses.…”

Stress-induced proton disorder in hydrous ringwoodite

“…1) were synthesized in a multianvil apparatus and characterized by electron microprobe analyses (EMPA) and secondary ion mass spectrometry (SIMS). Details of the experimental procedures and results of EMPA are given in Taran et al (2009) and Koch-Müller et al (2009); details of the SIMS measurements are given in Koch-Müller and Rhede (2010).…”