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Shock-induced effects in calcite from Cactus Crater

Vizgirda, J. and Ahrens, Thomas J. and Tsay, Fun-Dow (1980) Shock-induced effects in calcite from Cactus Crater. Geochimica et Cosmochimica Acta, 44 (8). pp. 1059-1069. ISSN 0016-7037. doi:10.1016/0016-7037(80)90059-9.

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Shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into the rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll, has been detected and quantified using electron spin resonance (ESR). ESR spectra of Mn^(2+), present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. A similar variation was observed in coral samples experimentally shocked to progressively higher pressures. It is speculated that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting and hence, small (< 0.01 Å) increases in cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models are suggested by the ESR results. One depicts a steady decay of the shock wave, from a maximum stress level of 4.5 GPa, at a rate, calculated in terms of post-flow co-ordinates, of d^(−5.7); this high attenuation rate may be due to the rocks underlying Cactus Crater having been displaced downward 5–6 m. The second delineates a breccia lens, possibly stratified, with a breccia-bedrock interface at 20 ± 5 m.

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Additional Information:© Pergamon Press Ltd 1980. Received 7 June 1979; Accepted in revised form 12 March 1980. The authors thank B. RISTVET for the initial introduction to the problem and for supplying the Eniwetok core samples. B. BINGHAM and S. HILL provided the X-ray results and R. HAACK the atomic absorption analyses. E. GELLE, R. SMITH and J. LONG assisted with the shock experiments. The helpful comments of H. Lowenstam and G. Rossman are much appreciated. We also thank M. DENCE for a careful and constructive review. This work was supported by the Defence Nuclear Agency under DNA001-76-C-0218. Contribution No. 3267, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.
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Defense Nuclear AgencyDNA001-76-C-0218
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Caltech Division of Geological and Planetary Sciences3267
Issue or Number:8
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Official Citation:Vizgirda, J., Ahrens, T. J., & Tsay, F.-D. (1980). Shock-induced effects in calcite from Cactus Crater. Geochimica et Cosmochimica Acta, 44(8), 1059-1069. doi:
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ID Code:51086
Deposited On:30 Oct 2014 21:48
Last Modified:10 Nov 2021 19:05

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