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Thermodynamic properties of Mg2SiO4 liquid at ultra-high pressures from shock measurements to 200 GPa

Summary: Thermodynamic properties of Mg2SiO4 liquid at ultra-high
pressures from shock measurements to 200 GPa
on forsterite and wadsleyite
Jed L. Mosenfelder,1
Paul D. Asimow,1
and Thomas J. Ahrens1,2
Received 24 February 2006; revised 22 November 2006; accepted 1 March 2007; published 30 June 2007.
[1] Polycrystalline samples of Mg2SiO4 forsterite and wadsleyite were synthesized and
then dynamically loaded to pressures of 39200 GPa. Differences in initial density
and internal energy between these two phases lead to distinct Hugoniots, each
characterized by multiple phase regimes. Transformation to the high-pressure phase
assemblage MgO + MgSiO3 perovksite is complete by 100 GPa for forsterite starting
material but incomplete for wadsleyite. The datum for wadsleyite shocked to 136 GPa,
however, is consistent with the assemblage MgO + MgSiO3 post-perovksite.
Marked increases in density along the Hugoniots of both phases between $130 and
150 GPa are inconsistent with any known solid-solid phase transformation in the
Mg2SiO4 system but can be explained by melting. Density increases upon melting are
consistent with a similar density increase observed in the MgSiO3 system. This
implies that melts with compositions over the entire Mg/Si range likely for the mantle
would be negatively or neutrally buoyant at conditions close to the core-mantle


Source: Asimow, Paul D. - Division of Geological and Planetary Sciences, California Institute of Technology,
Stewart, Sarah T. - Department of Earth and Planetary Sciences, Harvard University


Collections: Geosciences; Physics