The stability of divalent Ge in silicate melts and its geochemical properties

Eleanor Mare; Hugh St. C. O'Neill; Andrew Berry; Chris Glover

doi:10.1016/j.chemgeo.2019.119306

The stability of divalent Ge in silicate melts and its geochemical properties

Eleanor Mare, Hugh St. C. O'Neill, Andrew Berry, Chris Glover

School of Earth & Environmental Sciences

Research output: Contribution to journal › Article › peer-review

Abstract

The oxidation state of Ge in silicate glasses, quenched from melts, was determined by X-ray absorption spectroscopy. The melts were equilibrated over the range of relative oxygen fugacities (fO₂) from IW -3 to IW + 10, where IW is the iron-wüstite oxygen buffer in logarithmic units. X-ray absorption near edge structure (XANES) spectra of the samples show that over the range in fO₂ from IW -2.8 to IW + 2.4, the Ge⁴⁺/(Ge²⁺+ Ge⁴⁺) ratio increases from 0.05 to 0.95. Modelling of extended X-ray absorption fine structure (EXAFS) gives the Ge²⁺–O bond length as 1.89 ± 0.03 Å. Olivine–melt partitioning experiments were also conducted, which show that Ge²⁺ is highly incompatible, with D_Ge2+^ol/melt < 0.005, whereas D_Ge4+^ol/melt is ∼ 1, where D is the partition coefficient. The geochemical properties of Ge during the magmatic differentiation of the Moon and other reduced rocky planets and achondrite parent bodies will therefore be entirely different to that familiar from terrestrial examples. In particular, the incompatible nature of Ge2⁺may explain the anomalous enrichment of Ge in KREEP basalts.

Original language	English
Article number	119306
Journal	Chemical Geology
Volume	532
Early online date	2 Nov 2019
DOIs	https://doi.org/10.1016/j.chemgeo.2019.119306
Publication status	Published - 20 Jan 2020

Keywords

Germanium
Silicate melt
Oxidation state
XANES
EXAFS
Partitioning

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10.1016/j.chemgeo.2019.119306

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Copyright © 2019 Published by Elsevier B.V. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.chemgeo.2019.119306
Accepted author manuscript, 3.29 MBLicence: CC BY-NC-ND

Cite this

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title = "The stability of divalent Ge in silicate melts and its geochemical properties",

abstract = "The oxidation state of Ge in silicate glasses, quenched from melts, was determined by X-ray absorption spectroscopy. The melts were equilibrated over the range of relative oxygen fugacities (fO2) from IW -3 to IW + 10, where IW is the iron-w{\"u}stite oxygen buffer in logarithmic units. X-ray absorption near edge structure (XANES) spectra of the samples show that over the range in fO2 from IW -2.8 to IW + 2.4, the Ge4+/(Ge2+ + Ge4+) ratio increases from 0.05 to 0.95. Modelling of extended X-ray absorption fine structure (EXAFS) gives the Ge2+–O bond length as 1.89 ± 0.03 {\AA}. Olivine–melt partitioning experiments were also conducted, which show that Ge2+ is highly incompatible, with DGe2+ol/melt < 0.005, whereas DGe4+ol/melt is ∼ 1, where D is the partition coefficient. The geochemical properties of Ge during the magmatic differentiation of the Moon and other reduced rocky planets and achondrite parent bodies will therefore be entirely different to that familiar from terrestrial examples. In particular, the incompatible nature of Ge2+ may explain the anomalous enrichment of Ge in KREEP basalts.",

keywords = "Germanium, Silicate melt, Oxidation state, XANES, EXAFS, Partitioning",

author = "Eleanor Mare and O'Neill, {Hugh St. C.} and Andrew Berry and Chris Glover",

note = "HON gratefully acknowledges funding from the Australian Research Council through grant FL130100066.",

year = "2020",

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doi = "10.1016/j.chemgeo.2019.119306",

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volume = "532",

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TY - JOUR

T1 - The stability of divalent Ge in silicate melts and its geochemical properties

AU - Mare, Eleanor

AU - O'Neill, Hugh St. C.

AU - Berry, Andrew

AU - Glover, Chris

N1 - HON gratefully acknowledges funding from the Australian Research Council through grant FL130100066.

PY - 2020/1/20

Y1 - 2020/1/20

N2 - The oxidation state of Ge in silicate glasses, quenched from melts, was determined by X-ray absorption spectroscopy. The melts were equilibrated over the range of relative oxygen fugacities (fO2) from IW -3 to IW + 10, where IW is the iron-wüstite oxygen buffer in logarithmic units. X-ray absorption near edge structure (XANES) spectra of the samples show that over the range in fO2 from IW -2.8 to IW + 2.4, the Ge4+/(Ge2+ + Ge4+) ratio increases from 0.05 to 0.95. Modelling of extended X-ray absorption fine structure (EXAFS) gives the Ge2+–O bond length as 1.89 ± 0.03 Å. Olivine–melt partitioning experiments were also conducted, which show that Ge2+ is highly incompatible, with DGe2+ol/melt < 0.005, whereas DGe4+ol/melt is ∼ 1, where D is the partition coefficient. The geochemical properties of Ge during the magmatic differentiation of the Moon and other reduced rocky planets and achondrite parent bodies will therefore be entirely different to that familiar from terrestrial examples. In particular, the incompatible nature of Ge2+ may explain the anomalous enrichment of Ge in KREEP basalts.

AB - The oxidation state of Ge in silicate glasses, quenched from melts, was determined by X-ray absorption spectroscopy. The melts were equilibrated over the range of relative oxygen fugacities (fO2) from IW -3 to IW + 10, where IW is the iron-wüstite oxygen buffer in logarithmic units. X-ray absorption near edge structure (XANES) spectra of the samples show that over the range in fO2 from IW -2.8 to IW + 2.4, the Ge4+/(Ge2+ + Ge4+) ratio increases from 0.05 to 0.95. Modelling of extended X-ray absorption fine structure (EXAFS) gives the Ge2+–O bond length as 1.89 ± 0.03 Å. Olivine–melt partitioning experiments were also conducted, which show that Ge2+ is highly incompatible, with DGe2+ol/melt < 0.005, whereas DGe4+ol/melt is ∼ 1, where D is the partition coefficient. The geochemical properties of Ge during the magmatic differentiation of the Moon and other reduced rocky planets and achondrite parent bodies will therefore be entirely different to that familiar from terrestrial examples. In particular, the incompatible nature of Ge2+ may explain the anomalous enrichment of Ge in KREEP basalts.

KW - Germanium

KW - Silicate melt

KW - Oxidation state

KW - XANES

KW - EXAFS

KW - Partitioning

U2 - 10.1016/j.chemgeo.2019.119306

DO - 10.1016/j.chemgeo.2019.119306

M3 - Article

SN - 0009-2541

VL - 532

JO - Chemical Geology

JF - Chemical Geology

M1 - 119306

ER -

The stability of divalent Ge in silicate melts and its geochemical properties

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Keywords

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