Pressure and Temperature Dependence of the Univarian Boundary between Olivine and Wadsleyite in (Mg,Fe)2SiO4

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Pressure and Temperature Dependence of the Univarian Boundary between Olivine and Wadsleyite in (Mg,Fe)₂SiO₄

Jiuhua Chen, Donald J. Weidner (SUNY Stony Brook), Yanbin Wang (Univ. Chicago)

Oct., 1998

Conditions: 13-BM-D (bending magnet), energy-dispersive diffraction, beam size 0.1x0.2 mm, no focusing; T-cup apparatus in 250 ton LVP, 15 GPa, 1500 ° C

We use in-situ x-ray diffraction to determine the pressure and temperature dependence of the univariant boundary of the olivine-wadsleyite transition. Reversals of the phase transition were determined by the appearance and disappearance of the characteristic diffraction peaks of the two phases with varying the pressure and temperature. This data, combined with the lower pressure point determined at the NSLS, defines the Clapeyron slope of this geophysically important phase transition, which is most likely responsible for the 410 km seismic discontinuity.

Figure below shows the result. For comparison, results from previous quench experiments (Katsura and Ito, 1989) and non-reversed x-ray study (Kawada, 1979) are also shown.