Skip to Main content Skip to Navigation
Journal articles

Transformation weakening: Diffusion creep in eclogites as a result of interaction of mineral reactions and deformation

Holger Stunitz 1, 2, * K. Neufeld 1 R. Heilbronner 1 A.K. K Finstad 1 J. Konopásek 1, 3 J. R. Mackenzie 4 
* Corresponding author
2 Géodynamique - UMR7327
BRGM - Bureau de Recherches Géologiques et Minières (BRGM), ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327 : UMR7327, INSU - CNRS - Institut national des sciences de l'Univers, UO - Université d'Orléans : UMR7327
Abstract : The deformation of eclogites and the driving forces for their fabric development are an important topic, potentially allowing to determine deformation rates and stresses in subduction zones, where the greatest number of large earthquakes occurs. Here, fabric studies of grain size and shape, texture, and chemical composition from two locations of Variscan and Alpine eclogites are presented. All samples show a well-developed crystallographic preferred orientation (CPO) of omphacite with a strong maximum of [001] in the lineation direction and a weaker maximum of poles to (010) normal to foliation. Garnet shows no systematic CPO. Anisotropic chemical zoning developed in omphacite and garnet during growth together with elongated grain shapes and can be related to a prograde (in terms of pressure change) P,T-path. The individual chemically zoned and elongated grains orientated in the stretching direction are single crystals without major internal mis-orientations. Chemical, microstructural, and CPO data indicate that the deformation microstructure and texture were produced by preferential crystal growth of garnet and omphacite grains in the extension direction. Dislocation creep can be excluded as a possible fabric formation process by the systematic and oriented chemical zonation of single crystals and absence of dynamic recrystallization microstructures. The dominant deformation is inferred to be diffusion creep, where dissolution of material took place in reacting mafic phases (plagioclase, pyroxene) and precipitation took place in the form of new eclogite facies minerals (omphacite, garnet, zoisite). This type of diffusion creep deformation represents a transformation process involving both, deformation and metamorphic reactions. It is emphasized that the weakening is directly connected to the transformation and therefore transient. The weakening facilitates diffusion creep deformation of otherwise strong minerals (pyroxene, garnet, zoisite) at far lower stresses than dislocation creep. The results imply low stresses during the deformation of eclogite blocks in subduction zones. These results can be applied to other rock types, too.
Document type :
Journal articles
Complete list of metadata

Cited literature [115 references]  Display  Hide  Download
Contributor : Nathalie POTHIER Connect in order to contact the contributor
Submitted on : Tuesday, August 4, 2020 - 8:35:14 AM
Last modification on : Wednesday, August 3, 2022 - 4:05:18 AM
Long-term archiving on: : Monday, November 30, 2020 - 1:54:58 PM


Publication funded by an institution


Distributed under a Creative Commons Attribution 4.0 International License




Holger Stunitz, K. Neufeld, R. Heilbronner, A.K. K Finstad, J. Konopásek, et al.. Transformation weakening: Diffusion creep in eclogites as a result of interaction of mineral reactions and deformation. Journal of Structural Geology, Elsevier, 2020, 139, pp.104129. ⟨10.1016/j.jsg.2020.104129⟩. ⟨insu-02911575⟩



Record views


Files downloads