Luo, Sheng-Nian and Akins, Joseph A. and Ahrens, Thomas J. and Asimow, Paul D. (2004) Shock-compressed MgSiO_3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting. Journal of Geophysical Research B, 109 (B5). Art. No. B05205. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20120905-142013132
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Optical emission of MgSiO_3 glass, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry at discrete wavelengths ranging from visible to near infrared. We develop a new analysis of optical emission that does not require a gray body assumption. Instead, at each wavelength, the optical linear absorption coefficients (α) and blackbody spectral radiances (L_(λb)) of shocked and unshocked materials were obtained by nonlinear fitting to the time-resolved radiance from the target assembly. The absorption spectra of unshocked samples corresponding to the measured values of α reproduce those from independent static optical spectroscopic measurements. The measured values of α (ranging from 7 to 56 mm^(−1)) for shocked samples indicate that shock-induced high-pressure phases (including melt) can be regarded essentially as black bodies in the optical range investigated, although starting phases such as enstatite and olivine have band-like spectra at ambient conditions. The effect of emission from the air gap at the driver sample interface on the recorded radiance can be resolved, but α and L_(λb) cannot be separated for this component of the signal. The shock velocity-particle velocity relationships of these silicates derived from radiance history are in accord with previous investigations using independent techniques. Given the limited amount of shock wave data, possible high-pressure melting curves of Mg-perovskite and its assemblage with periclase are deduced; their melting temperatures near the core-mantle boundary (CMB) being 6000 ± 500 K and 4000 ± 300 K, respectively. It is proposed that Mg-perovskite melts with density increase at the CMB pressure.
|Additional Information:||© 2004 American Geophysical Union. Received 20 October 2003; revised 3 March 2004; accepted 10 March 2004; published 11 May 2004. This work was supported by U.S. National Science Foundation Grant No. EAR-0207934 (TJA and PDA). SNL is sponsored by a Director’s Post-doctoral Fellowship at Los Alamos National Laboratory (P-24 and EES-11). P. Gelle, M. Long and C. McCaughey supplied invaluable technical support. G. R. Rossman and E. Arrendondo kindly helped with optical spectroscopy measurements. C. Francis and S. Mackwell supplied the high-quality Sri Lanka enstatite crystals. We also benefited from discussions with X. L. Huang, S. D. Ni and D. C. Swift. The constructive suggestions by D. Heinz and I. Jackson are highly appreciated. Contribution No. 8951, Division of Geological and Planetary Sciences, California Institute of Technology.|
|Subject Keywords:||shock temperature, melting, equation of state, pyrometry, silicates, perovskite|
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|Official Citation:||Luo, S.-N., J. A. Akins, T. J. Ahrens, and P. D. Asimow (2004), Shock-compressed MgSiO3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting, J. Geophys. Res., 109, B05205, doi:10.1029/2003JB002860.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||05 Sep 2012 22:18|
|Last Modified:||26 Dec 2012 16:07|
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