HR: 0800h
AN: MR31B-0362    [Abstracts]
TI: Synthesis and Crystal Structure of Ferric-Rich MgSiO3-Perovskite
AU: * Catalli, K
EM: krystle@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Shim, S
EM: sangshim@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: GeoSoilEnviroCARS, Advanced Photon Source, Argonne National Lab, Argonne, IL 60439, United States
AU: Kubo, A
EM: kubo@cars.uchicago.edu
AF: GeoSoilEnviroCARS, Advanced Photon Source, Argonne National Lab, Argonne, IL 60439, United States
AU: Sturhahn, W
EM: sturhahn@aps.anl.gov
AF: Sector 3, Advanced Photon Source, Argonne National Lab, Argonne, IL 60439, United States
AU: Zhao, J
EM: jzhao@aps.anl.gov
AF: Sector 3, Advanced Photon Source, Argonne National Lab, Argonne, IL 60439, United States
AU: Kunz, M
EM: MKunz@lbl.gov
AF: Beamline 12.2.2, Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, United States
AU: Caldwell, W
EM: WACaldwell@lbl.gov
AF: Beamline 12.2.2, Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, United States
AB: Previous Mössbauer studies have shown that up to 50% of Fe in Mg silicate perovskite can be Fe³⁺ (McCammon 1997, Jackson et al. 2005). In order to measure the solubility of Fe³⁺ and the effect of Fe³⁺ on the crystal structure of Mg silicate in the lower mantle, we conducted X-ray diffraction and Mössbauer spectroscopy measurements in the laser-heated diamond-anvil cell using an Ar medium at sectors GSECARS and 3 at APS, and at beamline 12.2.2 at ALS. We observed the formation of orthorhombic (Pbnm) perovskite from MgSiO₃ enstatite and Fe₂O₃ hematite (25 and 50%) crystalline mixtures at 45-50 GPa after laser heating to 2000 K for 30 min. We also confirmed the synthesis of orthorhombic perovskite from glass starting materials with compositions of 90% MgSiO₃ + 10% Fe₂O₃ and 97.5% MgSiO₃ + 2.5% Fe₂O₃ at 50 GPa. This indicates that Mg silicate perovskite may have a large storage capacity for Fe³⁺ in the lower mantle. Our X-ray diffraction measurements show that 10% Fe₂O₃ expands the unit-cell volume of perovskite by as much as 2% at low pressure compared to pure Mg-endmember, but is more compressible than Mg-endmember perovskite. We also found that 10% Fe₂O₃ expands the b-axis by 0.5-0.7%, whereas the other axes are in agreement with those of Mg-endmember within experimental uncertainties to at least 65 GPa, indicating that Fe³⁺ expands the structure anisotropically.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting