Shear zones in the upper mantle: evidence from alpine- and ophiolite-type peridotite massifs Academic Article uri icon

abstract

  • AbstractThere is abundant field and microstructural evidence for localization of deformation in alpine- and ophiolite-type mantle massifs. On the basis of field relationships and microstructures we recognize two types of tectonite shear zones (medium- to coarse- and fine-grained), as well as two types of mylonitic shear zones (anhydrous and hydrous peridotite mylonites). In tectonite shear zones, softening processes responsible for localization are probably melt-related weakening in the medium to coarse tectonites and a change in limiting slip system in the fine-grained tectonites. In peridotite mylonites, the most likely cause for softening and localization is a change in dominant deformation mechanism from dislocation to grain size sensitive creep. Microstructural and petrological study of mylonite rocks reveals that reactions, either continuous net-transfer reactions (anhydrous and hydrous) or melt-rock reactions, play a key role in the formation of fine-grained material that promotes grain size sensitive creep. These reactions occur over a broad range of pressure-temperature conditions encompassing a large part of the lithospheric upper mantle. We conclude that mantle shear zones are widespread and that they reduce the (bulk) strength of the lithosphere significantly.

published proceedings

  • Geological Society, London, Special Publications

author list (cited authors)

  • Dijkstra, A. H., Drury, M. R., Vissers, R., Newman, J., & Van Roermund, H

citation count

  • 28

complete list of authors

  • Dijkstra, Arjan H||Drury, Martyn R||Vissers, Reinoud LM||Newman, Julie||Van Roermund, Herman LM

publication date

  • January 2004