A study of phase transformation in hedenbergite to 40 GPa at ∼1200° C |
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| Authors: | Young-Ho Kim Li Chung Ming Murli H Manghnani |
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| Institution: | 1. Hawaii Institute of Geophysics, University of Hawaii at Manoa, 2525 Correa Road, 96822, Honolulu, HI, USA
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| Abstract: | Phase transformations in a natural sample of hedenbergite ((Ca0.93Fe0.61Mn0.34Mg0.08Na0.01Zn0.02Al0.003)Si2O6) have been studied by X-ray diffraction up to 40 GPa at ∼ 1200°C in a diamond anvil cell interfaced with a laser heating
system. The starting hedenbergite phase decomposed into a garnet plus γ-spinel and stishovite at ∼ 14 GPa; then into garnet plus stishovite and wüstite at ∼ 18 GPa; and finally into perovskite
plus stishovite and wüstite at pressures higher than ∼ 24 GPa. On decompression to 0.1 MPa, all the high pressure phases are
retained except for the cubic perovskite, which reverts back into the ɛ-CaSiO3 phase, in accordance with previous reports. Energy-dispersive SEM analyses show that the garnet is present as a calcium-rich
ABO
3-type phase. As no garnet phase has been previously observed either in pure CaSiO3 or in pure CaMgSi2O6, it appears that the observed calcium-rich garnet phase has been stabilized by the presence of other cations such as the
Na+, Zn2+, Mn2+, Fe2+, Mn3+, Fe3+ and Al3+. |
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