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Shock temperatures in silica glass: Implications for modes of shock-induced deformation, phase transformation, and melting with pressure

Schmitt, Douglas R. and Ahrens, Thomas J. (1989) Shock temperatures in silica glass: Implications for modes of shock-induced deformation, phase transformation, and melting with pressure. Journal of Geophysical Research B, 94 (B5). pp. 5851-5871. ISSN 0148-0227. doi:10.1029/JB094iB05p05851.

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Gray body temperatures and emittances of silica glass under shock compression between 10 and 30 GPa are determined. Observed radiative temperatures are higher than computed continuum temperatures for shock-compressed silica glass; however, below ∼26 GPa observed emittances are <0.02. This suggests that fused quartz deforms heterogeneously in this shock pressure range as has been observed in other minerals. Between 10 and 16 GPa, radiative temperatures decrease from 4400 K to 3200 K, whereas above 16–30 GPa, gray body temperatures of ∼3000 K with low emittances are observed. The emittances increase with pressure from 0.02 to 0.9. The pressure range from 10 to 16 GPa coincides with the permanent densification region, while the 16–30 GPa range coincides with the inferred mixed phase region along the silica glass Hugoniot. The differing radiative behaviors may relate to these modes of deformation. Based upon earlier shock recovery experiments and a proposed model of heterogeneous deformation under shock compression, the temperatures associated with low emittances in the mixed phase region probably represent the melting temperature of the high-pressure phase, stishovite, which can be expected to crystallize from a melt in hot zones. Above 20 GPa the melting temperature of stishovite would therefore be 3000 K±200 K and almost independent of pressure to 30 GPa. The effects of pressure on melting relations for the system SiO_2–Mg_2SiO_4 are considered together with the proposed stishovite melting curve and suggested maximum solidus temperatures within the mantle of ∼2370 K at 12.5 GPa and ∼2530 K at 20.0 GPa. Using the proposed stishovite melting temperatures Tm and estimates of upper mantle temperatures T, the effective viscosity, which can be considered a function of the homologous temperature T/T_m, appears to remain nearly constant from 200 to 600 km depth in the Earth.

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Additional Information:Copyright 1989 by the American Geophysical Union. (Received November 17, 1987; revised December 6, 1988; accepted December 16, 1988.) Paper number 88JB04323. The authors wish to thank Epapradito Gelle, Michael Long, William Barber,and Wayne Miller for technical assistance. Discussions and aid from Gregory Miller, Philip Ihinger, William Anderson, Bob Svendsen, Michael Caroll, Peter Wyllie, and Brian Quinn were appreciated. This work supported under NSF grant EAR-86-08249 and NASA contract NGL-05-002-105. D. Schmitt gratefully acknowledges the support of the Sir James Lougheed Graduate Fellowship, Alberta Heritage Scholarship Fund, from 1984 to 1986. Contribution 4535, California Institute of Technology, Pasadena, California.
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Sir James Lougheed Graduate FellowshipUNSPECIFIED
Alberta Heritage Scholarship FundUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences4535
Issue or Number:B5
Record Number:CaltechAUTHORS:20141023-162859690
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Official Citation:Schmitt, D. R., and T. J. Ahrens (1989), Shock temperatures in silica glass: Implications for modes of shock-induced deformation, phase transformation, and melting with pressure, J. Geophys. Res., 94(B5), 5851–5871, doi:10.1029/JB094iB05p05851
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50761
Deposited By: George Porter
Deposited On:24 Oct 2014 14:49
Last Modified:10 Nov 2021 19:00

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