Synchrotron IR study of hydrous ringwoodite (γ-Mg2SiO4) up to 30 GPa |
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| Authors: | E M Chamorro Pérez I Daniel J-C Chervin P Dumas J D Bass T Inoue |
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| Institution: | (1) Laboratoire de Sciences de la Terre, CNRS UMR 5570 Ecole Normale Supérieure de Lyon, Université Claude Bernard Lyon 1, 46 allée d’Italie, 69364 Lyon cedex 07, France;(2) Institut de Minéralogie et de Physique des Milieux Condensés, Département de Physique des Milieux Denses, Université Pierre et Marie Curie CNRS-UMR7590, 140, rue de Lourmel, 75015 Paris, France;(3) Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin—BP 48, 91192 Gif-sur-Yvette, France;(4) Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green Street, Urbana, IL 61801, USA;(5) Geodynamics Research Center, Ehime University, Matsuyama, 790-8577 Ehime, Japan |
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| Abstract: | High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition. |
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| Keywords: | Hydrous ringwoodite High pressure Diamond anvil cell Infrared spectroscopy Synchrotron Mantle transition zone |
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