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Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join

Ahrens, Thomas J. and Asimow, Paul D. (2010) Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join. Journal of Geophysical Research B, 115 . Art. No. B10209. ISSN 0148-0227. doi:10.1029/2009JB007145.

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We determined the equation of state (EOS) of three silicate liquid compositions by shock compression of preheated samples up to 127 GPa. Diopside (Di; Ca_2Mg_2SiO_6) at 1773 K, anorthite (An; CaAl_2Si_2O_8) at 1923 K and the eutectic composition Di_(64)An_(36) at 1673 K were previously studied by shock compression to 38 GPa. The new data extend the EOS of each composition nearly to the Earth’s core-mantle boundary. The previously reported anomaly at 25 GPa for Di_(64)An_(36) eutectic was not reproduced; rather all data for this composition fit within error a straight line Hugoniot in particle velocity vs. shock velocity. Di also displays a linear Hugoniot consistent with ultrasonic data and a third-order finite strain EOS. The full anorthite data set is complex; we examine a model with a transition between two structural states and a fourth‐order finite strain model excluding two points that may not display relaxed behavior. We also report an experiment on room-temperature solid Di_(64)An_(36) aggregate that clearly demonstrates increase upon compression of the Grüneisen parameter of this liquid, much as experiment and theory have shown for forsterite and enstatite liquids. We construct isentropes and isotherms from our Hugoniots using Mie-Grüneisen thermal pressure and evaluate the model of ideal mixing of volumes. Volume may mix almost linearly at high temperature, but deviates strongly when calculated along an isotherm; it remains difficult to reach a firm conclusion. We compare the densities of liquids to lower mantle solids. Our results suggest that basaltic liquids rich in CaO and Al_2O_3 are notably denser than liquids in the MgO-SiO_2 binary and, subject to uncertainties in the behavior of FeO and in corrections for thermal pressure, such liquids may be the most likely candidates for achieving negative buoyancy in the lowermost mantle.

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Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2010 American Geophysical Union. Received 17 November 2009, revised 8 June 2010, accepted 30 June 2010, published 26 October 2010. This paper has taken many years of sustained effort by our irreplaceable technical staff: Michael Long, Eprapodito Gelle and Russel Oliver. Yongqin Jiao contributed to the very early stages and Daoyuan Sun made substantial contributions to the middle stage of the effort. Jed Mosenfelder provided the anorthite glass sample and frequent advice. Mark Ghiorso kindly carried out the fits of this data to his EOS formalism and shared prepublication results of his work with Frank Spera. This work was supported by the U. S. National Science Foundation through awards EAR‐0207934, EAR‐0409785, EAR‐0552009, EAR‐0555685, EAR‐0609804 and EAR‐0810116.
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Subject Keywords:Equation of state, Shock compression, Silicate liquids
Record Number:CaltechAUTHORS:20101129-141006829
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Official Citation:Asimow, P. D., and T. J. Ahrens (2010), Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join, J. Geophys. Res., 115, B10209, doi:10.1029/2009JB007145.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21044
Deposited By: Benjamin Perez
Deposited On:29 Nov 2010 23:24
Last Modified:09 Nov 2021 00:05

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