Shock-wave equation of state of rhyolite

Abstract

We have obtained new shock-wave equation of state (EOS) and release adiabat data for rhyolite. These data are combined with those of Swegle (1989, 1990) to give an experimental Hugoniot which is described by U_s = 2.53(±0.08) + 3.393(±0.37)u_p for u_p < 0.48 km s^(−1), U_s = 3.85(±0.05) + 0.65(±0.03)up for 0.48 ≤ u_p < 2.29 km s^(−1), U_s = 1.52(±0.08) + 1.67(±0.02)u_p for 2.29 ≤ u_p < 4.37 km s^(−1), and U_s = 3.40(±034) + 1.24(±0.06)u_p for u_p ≥ 4.37 km s^(−1), with ρ_0 = 2.357 ± 0.052 Mg m^(−3). We suggest that the Hugoniot data give evidence of three distinct phases—both low- and high-pressure solid phases and, possibly, a dense molten phase. EOS parameters for these phases are ρ_0 = 2.494 ± 0.002 Mg m^(−3), K_(S0) = 37 ± 2 GPa, K′ = 6.27 ± 0.25, and γ = 1.0(V/V_0) for the low-pressure solid phase; ρ_0 = 3.834 ± 0.080 Mg m^(−3), K_(S0) = 128 ± 20 GPa, K′ = 3.7 ± 1.4, and γ = 1.5 ± 0.5 for the solid high-pressure phase; and ρ_0 = 3.71 ± 0.10 Mg m^(−3), K_(S0) = 127 ± 25 GPa, K′ = 2.1 ± 1.0, and γ = 1.5 ± 1.0 for the dense liquid. Transition regions of the Hugoniot cover the ranges of 9–34 GPa for the low-pressure—high-pressure solid transition and 90–120 GPa for the high-pressure solid—liquid transition. Release paths from high-pressure states, calculated from the EOS parameters, suggest that the material remains in the high-pressure solid phase upon release. Release paths from both the high-pressure solid and liquid fall above the Hugoniot until the Hugoniot enters the low-pressure—high-pressure mixed phase region, when the release paths then cross the Hugoniot and fall below it, ending at significantly higher zero-pressure densities than that of the low-pressure phase. The low-pressure release paths fall very close to the Hugoniot. Estimates of residual heat deposition, based on shock-release path hysteresis, range from 20 to 60 per cent of the shock Hugoniot energy.