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Dynamic compression and volatile release of carbonates

Tyburczy, James A. and Ahrens, Thomas J. (1986) Dynamic compression and volatile release of carbonates. Journal of Geophysical Research B, 91 (B5). pp. 4730-4744. ISSN 0148-0227. doi:10.1029/JB091iB05p04730.

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Particle velocity profiles upon shock compression and adiabatic release were measured for polycrystalline calcite (Solenhofen limestone) to 12–24 GPa and for porous calcite (Dover chalk, ρ_o = 1.40 g/cm^3, 49% porosity) to between 5 and 11 GPa. The electromagnetic particle velocity gauge method was used. Upon shock compression of Solenhofen limestone, the Hugoniot elastic limit was determined to vary from 0.36 to 0.45 GPa. Transition shocks at between 2.5 and 3.7 GPa, possibly arising from the calcite II-III transition, were observed. For the Solenhofen limestone, the release paths lie relatively close to the Hugoniot. Evidence for the occurrence of the calcite III-II transition upon release was observed, but no rarefaction shocks were detected. Initial release wave speeds suggest retention of shear strength up to at least 20 GPa, with a possible loss of shear strength at higher pressures. The measured equation of state is used to predict the fraction of material devolatilized upon adiabatic release as a function of shock pressure. The effect of ambient partial pressure of CO_2 on the calculations is demonstrated. P_(CO_2) should be taken into account in models of atmospheric evolution by means of impact-induced mineral devolatilization. Mass fractions of CO_2 released expected on the basis of a continuum model are much lower than determined experimentally. This discrepancy, and radiative characteristics of shocked calcite, indicate that localization of thermal energy (shear banding) occurs under shock compression even though no solid-solid transitions occur in this pressure range. Release adiabatic data indicate that Dover chalk loses its shear strength when shocked to 10 GPa pressure. At 5 GPa the present data are ambiguous regarding shear strength. For Dover chalk, continuum shock entropy calculations result in a minimum estimate of 90% devolatilization upon complete release from 10 GPa. For calcite, isentropic release paths from calculated continuum Hugoniot temperatures cross into the CaO (solid) + CO_2 (vapor) field at improbably low pressures (for example, 10 GPa for a shock pressure of 25 GPa). However, calculated isentropic release paths originating from PT points corresponding to previous color temperature under shock measurements cross into the melt plus vapor field at pressures greater than 0.5 GPa, suggesting that devolatilization is initiated at the shear banding sites.

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Additional Information:Copyright 1986 by the American Geophysical Union. (Received November 26, 1984; revised August 5, 1985; accepted August 9, 1985.) Paper number 4B5363. We thank E. Gelle, M. Long, W. Miller, and C. Manning for their help in performing these experiments. M. Boslough, S. Rigden, and B. Svendsen provided valuable insight and discussion. The comments of anonymous reviewers helped improve the manuscript. Research supported by NASA NGL-05-002-105. Contribution 4134, Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences4134
Issue or Number:B5
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Official Citation:Tyburczy, J. A., and T. J. Ahrens (1986), Dynamic compression and volatile release of carbonates, J. Geophys. Res., 91(B5), 4730–4744, doi:10.1029/JB091iB05p04730.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51065
Deposited By: George Porter
Deposited On:30 Oct 2014 19:34
Last Modified:10 Nov 2021 19:05

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