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Science 1 July 1994:
Vol. 265. no. 5168, pp. 82 - 83
DOI: 10.1126/science.265.5168.82
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Articles

Pseudotachylytes Generated During Seismic Faulting and Eclogitization of the Deep Crust

H. Austrheim 1 and T. M. Boundy 2

1 Mineralogisk-Geologisk Museum, Sarsgt. 1, N-0562 Oslo, Norway
2 Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA.

Pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust. Pseudotachylytes in the Bergen arcs of western Norway contain microlites including omphacite, garnet, plagioclase, and quartz. This eclogite facies assemblage is stable at temperatures of about 800°C and pressures of 18 to 19 kilobars, corresponding to depths of 60 kilometers or more. The pseudotachylytes are exposed in Grenvillian granulites that locally underwent fluid-induced eclogitization and corresponding volume reduction of approximately 10 percent during the Caledonian continental collision. The pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process.

Submitted on January 4, 1994
Accepted on April 21, 1994


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