Journal Article

Distinguishing eclogite from peridotite: EBSD-based calculations of seismic velocities

James R. Worthington, Bradley R. Hacker and George Zandt

in Geophysical Journal International

Volume 193, issue 1, pages 489-505
Published in print April 2013 | ISSN: 0956-540X
Published online February 2013 | e-ISSN: 1365-246X | DOI: https://dx.doi.org/10.1093/gji/ggt004
Distinguishing eclogite from peridotite: EBSD-based calculations of seismic velocities

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Seismic velocities were calculated for 11 eclogites from the Western Gneiss Region, Norway, based on electron-backscatter diffraction (EBSD). The P-wave velocities are 8.0–8.5 km s–1 and the S-wave velocities are 4.5–4.8 km s–1; VP/VS1 (the ratio of P-wave to fast S-wave velocities) is 1.74–1.81. All the eclogites are relatively isotropic, with the higher anisotropies (3–4 per cent) in micaceous samples. Peridotite is comparatively more anisotropic (4–14 per cent more for P waves and up to 10 per cent more for S waves), and can have anomalously low VP/VS1, which may be useful means of distinguishing it from eclogite. Micaceous eclogite may be modelled using hexagonal anisotropy with a slow unique axis, whereas peridotite is most robustly modelled using orthorhombic anisotropy.

Keywords: Composition of the mantle; Body waves; Surface waves and free oscillations; Seismic anisotropy; Acoustic properties; Dynamics of lithosphere and mantle

Journal Article.  10299 words.  Illustrated.

Subjects: Geophysics

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