Articles | Volume 36, issue 6
https://doi.org/10.5194/ejm-36-1023-2024
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the Creative Commons Attribution 4.0 License.
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https://doi.org/10.5194/ejm-36-1023-2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
19 Dec 2024
Research article |
| 19 Dec 2024
| 19 Dec 2024
The coesite–stishovite transition of hydrous, Al-bearing SiO2: an in situ synchrotron X-ray study
Monika Koch-Müller
CORRESPONDING AUTHOR
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Christian Lathe
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Bernd Wunder
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Oona Appelt
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Shrikant Bhat
Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
Andreas Ebert
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Robert Farla
Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
Vladimir Roddatis
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Anja Schreiber
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
Richard Wirth
GFZ Helmholtz-Zentrum für Geoforschung, Telegrafenberg, 14473 Potsdam, Germany
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Dirk Spengler, Monika Koch-Müller, Adam Włodek, Simon J. Cuthbert, and Jarosław Majka
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Western Norwegian “diamond facies” eclogite contains tiny mineral inclusions of quartz and amphibole lamellae that are not stable in the diamond field. Low trace amounts of water in the lamellae-bearing host minerals suggest that the inclusion microstructure was not formed by fluid infiltration but by dehydration during early exhumation of these rocks. Some samples with higher water content argue that a late fluid overprint was spatially restricted and erased evidence of extreme metamorphism.
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We examined the reaction phase A plus high-P clinoenstatite to forsterite plus water (Reaction 1) by means of in situ X-ray diffraction measurements with the large volume press at the synchrotron PETRA III, Hamburg. Contrary to other studies, in which all experiments on Reaction (1) were performed at a water activity of 1, the reversed experiments presented in this study were performed at reduced water activity with mole fractions of about XH2O = XCO2 = 0.5.
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Carbonates reduce the melting point of the mantle, and carbonate melts produced in low-degree melting of a carbonated mantle are considered the precursor of CO2-rich magmas. We established experimentally the melting relations of carbonates up to 9 GPa, showing that Mg-carbonates melt incongruently to periclase and carbonate melt. The trace element signature of carbonate melts parental to kimberlites is approached by melting of Mg-rich carbonates.
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The equilibrium phase of A + HP clinoenstatite = forsterite + water was experimentally investigated at aH2O = 1 in situ. In cold subducting slabs, it is of relevance to transport water to large depths, initiating the formation of dense hydrous magnesium silicate (DHMS). At normal gradients, the huge water amount from this reaction induces important processes within the overlying mantle wedge. We additionally discuss the relevance of this reaction for intermediate-depth earthquake formation.
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Dense hydrous magnesium silicates, like the 3.65 Å phase, are thought to cause deep earthquakes. We investigated the dehydration of the 3.65 Å phase at P and T. In both directions of the investigated simple reaction, additional metastable water-rich phases occur. The observed extreme reduction in grain size in the dehydration experiments might cause mechanical instabilities in the Earth’s mantle and, finally, induce earthquakes.
Alice Taddei, Dan Holtstam, Erik Jonsson, Hans-Jürgen Förster, Stefan S. Andersson, Oona Appelt, and Luca Bindi
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Western Norwegian “diamond facies” eclogite contains tiny mineral inclusions of quartz and amphibole lamellae that are not stable in the diamond field. Low trace amounts of water in the lamellae-bearing host minerals suggest that the inclusion microstructure was not formed by fluid infiltration but by dehydration during early exhumation of these rocks. Some samples with higher water content argue that a late fluid overprint was spatially restricted and erased evidence of extreme metamorphism.
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This paper presents the results of an exploratory study on the pressure–volume–temperature behaviour of the main Mg-phosphates of geological interest, especially in high-pressure metamorphic rocks. The incentive for it was the growing body of experimental phase-equilibrium data acquired at high pressure in the MgO–(Al2O3)–P2O5–H2O systems, the thermodynamic evaluation of which has been begging for such volumetric data.
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Eur. J. Mineral., 36, 279–300, https://doi.org/10.5194/ejm-36-279-2024, https://doi.org/10.5194/ejm-36-279-2024, 2024
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We studied primary granitic and halogen-rich melt inclusions trapped in mantle rocks in the Bohemian Massif (Germany) in order to retrieve important information about the nature of the melt and the source rock. The melt was produced by the partial melting of metasediments during the deepest stages of subduction and interacted with the mantle. This work is an excellent example of transfer of crustal material, volatiles in particular, in the mantle during the subduction of the continental crust.
Christian Lathe, Monika Koch-Müller, Bernd Wunder, Oona Appelt, Melanie Sieber, Shrikant Bhat, and Robert Farla
Eur. J. Mineral., 35, 1149–1157, https://doi.org/10.5194/ejm-35-1149-2023, https://doi.org/10.5194/ejm-35-1149-2023, 2023
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We examined the reaction phase A plus high-P clinoenstatite to forsterite plus water (Reaction 1) by means of in situ X-ray diffraction measurements with the large volume press at the synchrotron PETRA III, Hamburg. Contrary to other studies, in which all experiments on Reaction (1) were performed at a water activity of 1, the reversed experiments presented in this study were performed at reduced water activity with mole fractions of about XH2O = XCO2 = 0.5.
Silvio Ferrero, Alessia Borghini, Laurent Remusat, Gautier Nicoli, Bernd Wunder, and Roberto Braga
Eur. J. Mineral., 35, 1031–1049, https://doi.org/10.5194/ejm-35-1031-2023, https://doi.org/10.5194/ejm-35-1031-2023, 2023
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Garnet often entraps small droplets of deep melts generated during mountain building processes. Using high-resolution techniques, we studied these droplets in order to provide hard numbers for the quantification of volatile budgets during crustal evolution, show how even melts formed at >1000°C contain water, and clarify how water behaves during metamorphism and melting at the microscale. Moreover, we provide the very first data on chlorine in natural melts from crustal reworking.
Melanie J. Sieber, Max Wilke, Oona Appelt, Marcus Oelze, and Monika Koch-Müller
Eur. J. Mineral., 34, 411–424, https://doi.org/10.5194/ejm-34-411-2022, https://doi.org/10.5194/ejm-34-411-2022, 2022
Short summary
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Carbonates reduce the melting point of the mantle, and carbonate melts produced in low-degree melting of a carbonated mantle are considered the precursor of CO2-rich magmas. We established experimentally the melting relations of carbonates up to 9 GPa, showing that Mg-carbonates melt incongruently to periclase and carbonate melt. The trace element signature of carbonate melts parental to kimberlites is approached by melting of Mg-rich carbonates.
Christian Lathe, Monika Koch-Müller, Bernd Wunder, Oona Appelt, Shrikant Bhat, and Robert Farla
Eur. J. Mineral., 34, 201–213, https://doi.org/10.5194/ejm-34-201-2022, https://doi.org/10.5194/ejm-34-201-2022, 2022
Short summary
Short summary
The equilibrium phase of A + HP clinoenstatite = forsterite + water was experimentally investigated at aH2O = 1 in situ. In cold subducting slabs, it is of relevance to transport water to large depths, initiating the formation of dense hydrous magnesium silicate (DHMS). At normal gradients, the huge water amount from this reaction induces important processes within the overlying mantle wedge. We additionally discuss the relevance of this reaction for intermediate-depth earthquake formation.
Monika Koch-Müller, Oona Appelt, Bernd Wunder, and Richard Wirth
Eur. J. Mineral., 33, 675–686, https://doi.org/10.5194/ejm-33-675-2021, https://doi.org/10.5194/ejm-33-675-2021, 2021
Short summary
Short summary
Dense hydrous magnesium silicates, like the 3.65 Å phase, are thought to cause deep earthquakes. We investigated the dehydration of the 3.65 Å phase at P and T. In both directions of the investigated simple reaction, additional metastable water-rich phases occur. The observed extreme reduction in grain size in the dehydration experiments might cause mechanical instabilities in the Earth’s mantle and, finally, induce earthquakes.
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Short summary
We examined the influence of Al2O3 and H2O on the position of the coesite–stishovite transition by means of in situ X‑ray diffraction measurements with the large-volume press at the synchrotron PETRA III in Hamburg. The position of the transition was found to be shifted almost in parallel by about 1.5 GPa to lower pressures compared to results for the pure SiO2 system by Ono et al. (2017). Stishovite of this study containing Al and H is only partially quenchable but transforms back to coesite.
We examined the influence of Al2O3 and H2O on the position of the coesite–stishovite transition...
Special issue