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OH-defects in multiple-doped orthoenstatite at 4-8 GPa: filling the gap between pure and natural systems.

Stalder R, Karimova A, Konzett J - Contrib Mineral Petrol (2015)

Bottom Line: Conversely, in Al-poor systems without garnet, total OH is positively correlated with pressure, and both trends intersect around 8 GPa and ~1000 wt ppm H2O.IR-spectra of enstatite reveal several pressure sensitive features, such as (1) the absorbance of the absorption band at 3687 cm(-1), (2) the band position near 3400 cm(-1) and (3) the ratio (A 3240-3570/A 3240-3730) and their application as geobarometer in natural samples are evaluated.For garnet-bearing phase assemblages, the band ratio (A 3240-3570/A 3240-3730) in orthoenstatite defines a pressure trend in between that observed in the pure system MgO-SiO2-H2O and that found in orthopyroxenes from natural mantle peridotites, suggesting that the application of IR-spectra as proxy for pressure is justified.

View Article: PubMed Central - PubMed

Affiliation: Institut für Mineralogie und Petrographie, Universität Innsbruck, Innrain 52 f, 6020 Innsbruck, Austria.

ABSTRACT

OH-defects in orthoenstatite were studied experimentally between 4 and 8 GPa at 1150 °C in the system CaO-MgO-Al2O3-SiO2-Cr2O3-Na2O, leading to phase assemblages enstatite ± forsterite ± diopside ± garnet. In enstatite coexisting with garnet, total OH is negatively correlated with pressure. Conversely, in Al-poor systems without garnet, total OH is positively correlated with pressure, and both trends intersect around 8 GPa and ~1000 wt ppm H2O. IR-spectra of enstatite reveal several pressure sensitive features, such as (1) the absorbance of the absorption band at 3687 cm(-1), (2) the band position near 3400 cm(-1) and (3) the ratio (A 3240-3570/A 3240-3730) and their application as geobarometer in natural samples are evaluated. For garnet-bearing phase assemblages, the band ratio (A 3240-3570/A 3240-3730) in orthoenstatite defines a pressure trend in between that observed in the pure system MgO-SiO2-H2O and that found in orthopyroxenes from natural mantle peridotites, suggesting that the application of IR-spectra as proxy for pressure is justified.

No MeSH data available.


Evolution of the slope in the band ratio—pressure trend (Fig. 3) with increasing complexity of the chemical system. The large errors for 1 and 2 are due to the large range of band ratios. Data sources: 1 Prechtel and Stalder (2011), 2 Stalder (2004), 3 Prechtel and Stalder (2012), 4 this study, 5 Prechtel and Stalder (2012)
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Fig9: Evolution of the slope in the band ratio—pressure trend (Fig. 3) with increasing complexity of the chemical system. The large errors for 1 and 2 are due to the large range of band ratios. Data sources: 1 Prechtel and Stalder (2011), 2 Stalder (2004), 3 Prechtel and Stalder (2012), 4 this study, 5 Prechtel and Stalder (2012)

Mentions: Based on the results of the present study, it is not possible to satisfactorily explain the discrepancy in H2O contents of enstatite between the synthetic bulk systems of this study and natural systems. One general problem for natural systems is broad and overlapping absorption bands that makes the quantitative characterisation of the defect chemistry and thermodynamic modelling very complicated. Although the observed trend of IR band ratios for enstatite from the Na–Ca–Al–Cr-doped system does not reproduce the trend observed in natural orthopyroxene from mantle xenoliths, the results of this study are a further step towards closing the gap between pure end member and natural system behaviour (Fig. 9), suggesting that it is justified to apply the band ratio (A3240–3570/A3240–3730) in natural enstatite as geobarometer.Fig. 9


OH-defects in multiple-doped orthoenstatite at 4-8 GPa: filling the gap between pure and natural systems.

Stalder R, Karimova A, Konzett J - Contrib Mineral Petrol (2015)

Evolution of the slope in the band ratio—pressure trend (Fig. 3) with increasing complexity of the chemical system. The large errors for 1 and 2 are due to the large range of band ratios. Data sources: 1 Prechtel and Stalder (2011), 2 Stalder (2004), 3 Prechtel and Stalder (2012), 4 this study, 5 Prechtel and Stalder (2012)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig9: Evolution of the slope in the band ratio—pressure trend (Fig. 3) with increasing complexity of the chemical system. The large errors for 1 and 2 are due to the large range of band ratios. Data sources: 1 Prechtel and Stalder (2011), 2 Stalder (2004), 3 Prechtel and Stalder (2012), 4 this study, 5 Prechtel and Stalder (2012)
Mentions: Based on the results of the present study, it is not possible to satisfactorily explain the discrepancy in H2O contents of enstatite between the synthetic bulk systems of this study and natural systems. One general problem for natural systems is broad and overlapping absorption bands that makes the quantitative characterisation of the defect chemistry and thermodynamic modelling very complicated. Although the observed trend of IR band ratios for enstatite from the Na–Ca–Al–Cr-doped system does not reproduce the trend observed in natural orthopyroxene from mantle xenoliths, the results of this study are a further step towards closing the gap between pure end member and natural system behaviour (Fig. 9), suggesting that it is justified to apply the band ratio (A3240–3570/A3240–3730) in natural enstatite as geobarometer.Fig. 9

Bottom Line: Conversely, in Al-poor systems without garnet, total OH is positively correlated with pressure, and both trends intersect around 8 GPa and ~1000 wt ppm H2O.IR-spectra of enstatite reveal several pressure sensitive features, such as (1) the absorbance of the absorption band at 3687 cm(-1), (2) the band position near 3400 cm(-1) and (3) the ratio (A 3240-3570/A 3240-3730) and their application as geobarometer in natural samples are evaluated.For garnet-bearing phase assemblages, the band ratio (A 3240-3570/A 3240-3730) in orthoenstatite defines a pressure trend in between that observed in the pure system MgO-SiO2-H2O and that found in orthopyroxenes from natural mantle peridotites, suggesting that the application of IR-spectra as proxy for pressure is justified.

View Article: PubMed Central - PubMed

Affiliation: Institut für Mineralogie und Petrographie, Universität Innsbruck, Innrain 52 f, 6020 Innsbruck, Austria.

ABSTRACT

OH-defects in orthoenstatite were studied experimentally between 4 and 8 GPa at 1150 °C in the system CaO-MgO-Al2O3-SiO2-Cr2O3-Na2O, leading to phase assemblages enstatite ± forsterite ± diopside ± garnet. In enstatite coexisting with garnet, total OH is negatively correlated with pressure. Conversely, in Al-poor systems without garnet, total OH is positively correlated with pressure, and both trends intersect around 8 GPa and ~1000 wt ppm H2O. IR-spectra of enstatite reveal several pressure sensitive features, such as (1) the absorbance of the absorption band at 3687 cm(-1), (2) the band position near 3400 cm(-1) and (3) the ratio (A 3240-3570/A 3240-3730) and their application as geobarometer in natural samples are evaluated. For garnet-bearing phase assemblages, the band ratio (A 3240-3570/A 3240-3730) in orthoenstatite defines a pressure trend in between that observed in the pure system MgO-SiO2-H2O and that found in orthopyroxenes from natural mantle peridotites, suggesting that the application of IR-spectra as proxy for pressure is justified.

No MeSH data available.