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

Abstract

[1] 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 2 Mg 2 SiO 6 ) at 1773 K, anorthite (An; CaAl 2 Si 2 O 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 2 O 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.Citation: Asimow, P. D., and T. J. Ahrens (2010), Shock compression of liquid silicates to 125 GPa: The anorthite-diopside join,

Shock compression of preheated silicate liquids: Apparent universality of increasing Grüneisen parameter upon compression

“…The value of γ at ambient conditions is 0.356 [11]. The value at high P was tightly constrained by Asimow and Ahrens [12] from the combination of several pre-heated liquid Hugoniot data and a single high-precision Hugoniot point on an isochemical room-temperature solid aggregate of diopside and anorthite. The difference between the Hugoniots in U s -u p space gives q = -1.63.…”

Thermodynamically complete equation of state of MgO from true radiative shock temperature measurements on samples preheated to 1850 K

“…The experimental technique applied in this work combined two previously developed methods: high-speed, plate impact shock experiments on samples preheated up to 1932 K [31] and conventional fast multiwavelength optical pyrometry [32]. The main features of the experimental design were already reported in sufficient detail [28].…”

Structure of shock compressed model basaltic glass: Insights from O K‐edge X‐ray Raman scattering and high‐resolution27Al NMR spectroscopy

“…Electron probe analysis is given by Asimow and Ahrens [2010]; the composition is close to the nominal Di 64 An 36 eutectic, with minor Na 2 O (0.067 AE 0.021 wt.%) and barely resolved FeO (0.018 AE 0.016 wt.%). A disk 0.5 mm thick of 5 mm diameter was loaded into a cavity in a stainless steel 304 (SS304) chamber with 5.5 mm of steel between impact surface and sample, acting as driver.…”

“…[5] The starting glass was prepared as documented by Asimow and Ahrens [2010] by powdering, mixing, and melting initial glasses with diopside and anorthite composition synthesized by Dow Corning Corporation. Electron probe analysis is given by Asimow and Ahrens [2010]; the composition is close to the nominal Di 64 An 36 eutectic, with minor Na 2 O (0.067 AE 0.021 wt.%) and barely resolved FeO (0.018 AE 0.016 wt.%).…”

“…Knowing the structures of shock compressed basaltic glasses also provide an atomistic understanding of the geophysical processes involving basaltic magmas in the Earth's interior [Asimow and Ahrens, 2010;Rigden et al, 1988]. The Ca-Mg aluminosilicate melt of diopside-anorthite eutectic composition (Di 64 An 36 ) can serve as a model system for basaltic melts [Ai and Lange, 2008;Milholland and Presnall, 1998].…”