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In situ simultaneous Fe K-edge XAS spectroscopy and resistivity measurements of riebeckite - Implications for anomalous electrical conductivity in subduction zones

At a Glance

Section titled ā€œAt a Glanceā€
MetadataDetails
Publication Date2023-10-06
JournalGeochemistry
AuthorsGiancarlĪæ Della Ventura, Federico Galdenzi, A. Marcelli, Giannantonio Cibin, Roberta Oberti
InstitutionsRoma Tre University, UniversitƤt Hamburg
Citations7

Abstract

Section titled ā€œAbstractā€

In this paper, we address two key features of the behaviour of Fe-rich amphibole at high temperatures: (1) the Fe2+ ā†’ Fe3+ + eāˆ’ exchange within the crystal bulk, and (2) the consequent rise in electrical conductivity. Cycling heating-cooling experiments were done in situ up to 542 Ā°C (815 K) at beamline B11 of the Diamond Synchrotron Laboratory (UK). X-ray absorption spectra at the Fe K-edge and electrical resistivity were measured simultaneously on a single crystal of riebeckite with a composition very close to the ideal formula Aā–”BNa2C(Fe2+3Fe3+2)TSi8O22W(OH)2. The Fe3+/Fetot ratio was monitored via analysis of the pre-edge feature in the XANES spectra. Our data show slight oscillations of the oxidation state of Fe with temperature cycling up to around 400 Ā°C (673 K), followed by a substantial gradual increase in Fe2+ ā†’ Fe3+ oxidation that starts at ~450 Ā°C (~723 K) and is completed at ~525 Ā°C (~798 K). The conductivity (Ļƒ) measured along the crystallographic c-axis oscillates strongly with cycling temperature allowing us to conclude that it is intrinsically related to the electron hopping induced by thermal treatment. The activation-energy derived from the Ļƒ(T) trend is Ea = 74.4 Ā± 0.6 kJ/mol (0.77 Ā± 0.01 eV), in agreement with small-polaron conduction. This study provides direct and robust support of the conduction mechanisms in Fe-amphibole previously inferred from indirect methods. Given that riebeckite is a significant component in the glaucophanitic amphiboles common in blueschists associated with subducted oceanic crust, our data provide a link between atomic-scale processes and Earth-scale anomalous conductivity observed via geophysical measurements.

Tech Support

Section titled ā€œTech Supportā€

Original Source

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References

Section titled ā€œReferencesā€
  1. 2018 - Potential for porphyry copper deposits in northern Tohoku [Crossref]
  2. 2023 - Thermally activated electron hopping in Fe-rich amphiboles: implications for the high-conductivity anomalies in subduction zones [Crossref]
  3. 2004 - Low electrical resistivity associated with plunging of the Nazca flat slab beneath Argentina [Crossref]
  4. 2017 - Dehydration of phengite inferred by electrical conductivity measurements: implication for the high conductivity anomalies relevant to the subduction zones [Crossref]
  5. 1995 - Seismic velocity structure and composition of the continental crust: a global view [Crossref]
  6. 2018 - The dynamics of Fe oxidation in riebeckite: a model for amphiboles [Crossref]
  7. 2018 - Iron oxidation dynamics vs. temperature of synthetic potassic-ferro-richterite: a XANES investigation [Crossref]
  8. 2013 - Performance of B18, the core EXAFS bending magnet beamline at diamond [Crossref]

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