Deformation mechanisms of plagioclase and seismic anisotropy of the Acebuches metabasites (SW Iberian massif)

Author:

Díaz-Azpiroz Manuel1,Lloyd Geoffrey E.2,Fernández Carlos3

Affiliation:

1. Departamento de Sistemas Físicos, Químicos y Naturales. Universidad Pablo de Olavide, Crtra. Utrera, 41013 Seville, Spain

2. School of Earth & Environment, University of Leeds, Leeds, LS2 9JT UK

3. Departamento de Geodinámica y Paleontología, Facultad de Ciencias Experimentales, Universidad de Huelva, Campus de El Carmen, 21071 Huelva

Abstract

AbstractSamples of the Acebuches metabasites (SW Spain), deformed under low-pressure/medium-to-high temperature metamorphic conditions, have been analysed via electron backscattered diffraction (EBSD) to obtain their plagioclase crystal lattice preferred orientations (LPO). Plagioclases from the highest temperature amphibolites show moderate LPO and a good correlation between 180° misorientation angles and both the crystal and the kinematic coordinate systems, which is attributed to dislocation glide accommodated by mechanical albite+pericline twinning. Plagioclases from medium-temperature amphibolites exhibit well-developed LPO, suggesting that dislocation creep was active during plagioclase deformation. Plagioclases from the more intensively deformed mafic schists exhibit weak LPO, indicating the activity of LPO-destroying deformation mechanisms. Evidence points to grain-boundary sliding accompanied by limited fracturing. The observed LPO are characterized by the alignment of [100] parallel to the kinematicX-direction. This association suggests that [100] was the preferential slip direction during dislocation creep of plagioclase, with (010) and/or (001) appearing to have acted as the dominant slip planes. The observed plagioclase LPO is combined with hornblende LPO to define the seismic fabric of the Acebuches metabasites. In samples with strong plagioclase LPO, the resulting seismic fabrics are highly influenced by this phase.

Publisher

Geological Society of London

Subject

Geology,Ocean Engineering,Water Science and Technology

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