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