@article{a720c64193fa4eb2a49c58c5b837ceac,
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 = "EXAFS, Germanium, Oxidation state, Partitioning, Silicate melt, XANES",
author = "Mare, {Eleanor R.} and O'Neill, {Hugh St C.} and Berry, {Andrew J.} and Glover, {Chris J.}",
note = "Funding Information: The authors acknowledge the scientific and technical assistance of the Australian Microscopy and Microanalysis Research Facility at the Centre of Advanced Microscopy, Australian National University. The spectroscopy part of this research was undertaken at the XAS beamline of the Australian Synchrotron, which is part of ANSTO. Peter Kappen, Bernt Johannessen and Jeremy Wykes are thanked for technical assistance at the beamline. Mark Ridgway is thanked for providing Ge0 standards. Jung-Woo Park, Mike Jollands, Peter Tollan, James Tolley and Robert Rapp are thanked for technical assistance with LA-ICPMS and EPMA. The authors acknowledge an anonymous reviewer whose feedback was very useful in improving the manuscript. HON gratefully acknowledges funding from the Australian Research Council through grant FL130100066. Funding Information: The authors acknowledge the scientific and technical assistance of the Australian Microscopy and Microanalysis Research Facility at the Centre of Advanced Microscopy, Australian National University. The spectroscopy part of this research was undertaken at the XAS beamline of the Australian Synchrotron, which is part of ANSTO. Peter Kappen, Bernt Johannessen and Jeremy Wykes are thanked for technical assistance at the beamline. Mark Ridgway is thanked for providing Ge 0 standards. Jung-Woo Park, Mike Jollands, Peter Tollan, James Tolley and Robert Rapp are thanked for technical assistance with LA-ICPMS and EPMA. The authors acknowledge an anonymous reviewer whose feedback was very useful in improving the manuscript. HON gratefully acknowledges funding from the Australian Research Council through grant FL130100066 . Appendix A Publisher Copyright: {\textcopyright} 2019",
year = "2020",
month = jan,
day = "20",
doi = "10.1016/j.chemgeo.2019.119306",
language = "English",
volume = "532",
journal = "Chemical Geology",
issn = "0009-2541",
publisher = "Elsevier BV",
}