DI023-0013
Equation of State of Al-rich Phase δ-H: Behavior of Ferric Iron in a High-Pressure Oxyhydroxide

Tuesday, 15 December 2020
Poster
Benjamin Strozewski1, Johannes Buchen1, Wolfgang Sturhahn1, Itaru Ohira2, Takayuki Ishii3, Stella Chariton4, Thomas Toellner5 and Jennifer M Jackson1, (1)California Institute of Technology, Seismological Laboratory, Pasadena, CA, United States, (2)Ehime University, Geodynamics Research Center, Ehime, Japan, (3)University of Bayreuth, Bayerisches Geoinstitut, Bayreuth, Germany, (4)University of Chicago, Center for Advanced Radiation Sources, Chicago, IL, United States, (5)Argonne National Laboratory, Advanced Photon Source, Argonne, IL, United States
Abstract:
High-pressure oxyhydroxide phases of (Al,Fe)OOH (phase δ)–MgSiO2(OH)2 (phase H) solid solutions are stable at pressures and temperatures of Earth’s lower mantle [1, 2]. The stability of these phases implies that H2O may be transported into the lower mantle by cold, subducting slabs. The compression behavior of the high-pressure oxyhydroxides may be affected by changes in hydrogen bonding as well as by changes in the electronic structure of Fe3+, making identification of multiple phase transitions in these phases crucial [3,4]. To constrain the effect of the spin transition of ferric iron on the properties of the high-pressure oxyhydroxides, we have determined the equation of state of Al-rich phase δ-H to pressures of ~55 GPa.

Powdered Al-rich phase δ-H with composition Mg0.03Al0.83Si0.06Fe0.08O(OH) was loaded in a symmetric diamond anvil cell and characterized using synchrotron Mössbauer spectroscopy at beamline 3-ID-D of the Advanced Photon Source (APS), Argonne National Laboratory. The diamond anvil cell was connected to a membrane-driven pressure control system at APS beamline 13-ID-D (GSECARS) for X-ray diffraction studies. Helium was used as the pressure-transmitting medium. Pressures were determined from the unit cell volumes of gold. X-ray diffraction patterns were collected at approximately 0.5 GPa pressure steps in the range ~4.5-54 GPa. Common background intensity of the diffraction patterns was removed using the MINUTI sbck module (https://www.nrixs.com). Subsequently, we refined unit cell parameters of Al-rich phase δ-H and gold. We fit the resulting pressure-volume data with a model that accounts for the compression-induced spin transition in Fe3+. We compare the results with previous high-pressure experiments on phase δ and phase H and discuss possible effects of the spin transition of ferric iron on high-pressure oxyhydroxides.

  1. Nishi, M. et al. Geosci. 7, 224–227 (2014). https://doi.org/10.1038/ngeo2074
  2. Ohira, I. et al. Earth Planet. Sci. Lett. 401, 12-17 (2014). https://doi.org/10.1016/j.epsl.2014.05.059
  3. Ohira, I. et al. Mineral. 104, 1273–1284 (2019). https://doi.org/10.2138/am-2019-6913
  4. Sano-Furukawa, A. et al. Rep. 8, 15520 (2018). https://doi.org/10.1038/s41598-018-33598-2
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