Coupled inter-site reaction and diffusion: Rapid dehydrogenation of silicon vacancies in natural olivine

Jollands, Michael C.; Kempf, Elias; Hermann, Jörg; Müntener, Othmar

doi:10.1016/j.gca.2019.07.025

Cited by 29 publications

(32 citation statements)

References 69 publications

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“…This hypothesis is based on the assumption that there is no diffusional equilibration of H in Si-vacancies in olivine with further subduction. A recent experimental study on the Zermatt olivines (sample Ol1-2) from this outcrop by Jollands et al ( 2019 ) has shown that at atmospheric pressures the Si-vacancies are dehydrogenated within hours at elevated temperatures. However, the study also showed that dehydrogenation in 1 atm experiments is not easily extrapolated to natural conditions and that H loss or gain is governed by a complex interplay of inter-site reactions and diffusion.…”

Section: Discussionmentioning

confidence: 97%

The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland)

et al. 2020

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Metamorphic olivine formed by the reaction of antigorite + brucite is widespread in serpentinites that crop out in glacier-polished outcrops at the Unterer Theodulglacier, Zermatt. Olivine overgrows a relic magnetite mesh texture formed during ocean floor serpentinization. Serpentinization is associated with rodingitisation of mafic dykes. Metamorphic olivine coexists with magnetite, shows high Mg# of 94–97 and low trace element contents. A notable exception is 4 µg/g Boron (> 10 times primitive mantle), introduced during seafloor alteration and retained in metamorphic olivine. Olivine incorporated 100–140 µg/g H2O in Si-vacancies, providing evidence for low SiO2-activity imposed by brucite during olivine growth. No signs for hydrogen loss or major and minor element diffusional equilibration are observed. The occurrence of olivine in patches within the serpentinite mimics the former heterogeneous distribution of brucite, whereas the network of olivine-bearing veins and shear zones document the pathways of the escaping fluid produced by the olivine forming reaction. Relic Cr-spinels have a high Cr# of 0.5 and the serpentinites display little or no clinopyroxene, indicating that they derive from hydrated harzburgitic mantle that underwent significant melt depletion. The enrichment of Mg and depletion of Si results in the formation of brucite during seafloor alteration, a pre-requisite for later subduction-related olivine formation and fluid liberation. The comparison of calculated bulk rock brucite contents in the Zermatt-Saas with average IODP serpentinites suggests a large variation in fluid release during olivine formation. Between 3.4 and 7.2 wt% H2O is released depending on the magnetite content in fully serpentinized harzburgites (average oceanic serpentinites). Thermodynamic modelling indicates that the fluid release in Zermatt occurred between 480 °C and 550 °C at 2–2.5 GPa with the Mg# of olivine varying from 68 to 95. However, the majority of the fluid released from this reaction was produced within a narrow temperature field of < 30 °C, at higher pressures 2.5 GPa and temperatures 550–600 °C than commonly thought. Fluids derived from the antigorite + brucite reaction might thus trigger eclogite facies equilibration in associated metabasalts, meta-gabbros, meta-rodingites and meta-sediments in the area. This focused fluid release has the potential to trigger intermediate depths earthquakes at 60–80 km in subducted oceanic lithosphere.

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Section: Discussionmentioning

confidence: 97%

The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland)

et al. 2020

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“…4-7. These discrepancies between different studies have stimulated several controversies and ongoing debates (e.g., Karato and Dai, 2009;, 2013Jones, 2014Jones, , 2016Gardés et al, 2015;Dai and Karato, 2015). Importantly, the inconsistencies in the experimental data reported by different researchers have led to large differences in the estimated water content of the UM and MTZ and also created great confusion for the geoscience community.…”

Section: Discrepancies and Interpretationsmentioning

confidence: 99%

“…Consequently, the laboratorybased laws of NAMs' electrical conductivity predict contrasting effects of water, precluding the interpretation of geophysical data in terms of mantle hydration. We found that several researchers Jones, 2014;Karato, 2019) have attempted to develop a unified law to reconcile the large discrepancies in available data on olivine conductivity and test the internal consistency of the database. They argued that the experimental data from different laboratory studies are mostly consistent when the uncertainties and biases in the water contents of the olivine samples are considered.…”

Section: Discrepancies and Interpretationsmentioning

confidence: 99%

Influence of water on the physical properties of olivine, wadsleyite, and ringwoodite

Zhang

Xia

2021

Eur. J. Mineral.

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Abstract. The incorporation of water in nominally anhydrous minerals plays a crucial role in many geodynamic processes and evolution of the Earth and affects the physical and chemical properties of the main constituents of the Earth's mantle. Technological advances now allow the transport properties of minerals to be precisely measured under extreme conditions of pressure and temperature (P and T) that closely mimic the P–T conditions throughout much of the Earth's interior. This contribution provides an overview of the recent progress in the experimental studies on the influence of water on physical properties (i.e., diffusivity, electrical conductivity, thermal conductivity, sound velocity, and rheology) of olivine, wadsleyite, and ringwoodite together with their applications. In particular, consistency among various experimental data is investigated, discrepancies are evaluated, and confusions are clarified. With such progress in the experimental determination of transport properties of major mantle minerals, we can expect new insights into a broad range of geoscience problems. Many unresolved issues around water inside Earth require an integrated approach and concerted efforts from multiple disciplines.

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“…Several studies have reported site-specific diffusivities and re-distribution of hydrogen defects in natural clinopyroxene and olivine at high temperatures (Ferriss et al 2016(Ferriss et al , 2018Jollands et al 2019;Thoraval et al 2019;Ya ng et al 2019aYa ng et al , 2019b.…”

Section: These Intricate Features Of Hydrogen Defects Observed In Natmentioning

confidence: 99%

Behavior and origin of hydrogen defects in natural orthopyroxene during high-temperature processes

Yang

Ingrin

Liu

et al. 2021

American Mineralogist

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Spectral features of hydrogen defects in natural mantle minerals derive from physico-chemical conditions of the lithosphere. Although hydrogen defects in synthetic orthopyroxene have been well investigated, their complex spectral features in natural orthopyroxenes are still difficult to decipher. To clarify this issue, it is indispensable to reveal what happens to hydrogen defects during high temperature processes, thereby fingerprinting the origins of hydrogen defects observed in natural orthopyroxene. Here, we carry out Fourier transform infrared spectroscopic studies on hydrogen defects of three natural orthopyroxenes at elevated temperatures to 1000 o C. Hydrogen defects display reversible disordering at temperatures above 700 o C, which is different to those at ambient conditions. Moreover, hydrogen diffusivities are significantly different between the orthopyroxene samples from different tectonic settings despite their similar iron contents. Even for the same crystal, different hydrogen defects display different diffusion behaviors. Hydrogen defects corresponding to the 3420 cm-1 band have the fastest diffusivity relative to the other hydrogen defects. Most importantly, hydrogen defects can redistribute in the crystal, with new hydrogen defects produced at the cost of the initial hydrogen defects rather than involving reaction with an external hydrogen source. Combining these findings with previously reported hydrogen defects in natural olivine and clinopyroxene at high temperatures, we propose that (1) to correctly relate hydrogen defects features to geological processes, it is imperative to understand their behavior and origin, (2) hydrogen disordering should be taken into account when predicting and extrapolating This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Coupled inter-site reaction and diffusion: Rapid dehydrogenation of silicon vacancies in natural olivine

Cited by 29 publications

References 69 publications

The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland)

The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland)

Influence of water on the physical properties of olivine, wadsleyite, and ringwoodite

Behavior and origin of hydrogen defects in natural orthopyroxene during high-temperature processes

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