Modification of Antiphase Domain Sizes in Omphacite by Dislocation Glide and Creep Mechanisms and Its Petrological Consequences

H. L. M. van Roermund* and J. M. Lardeaux
Ecole Normale Supérieure de Lyon, Lab. des Sciences de la Terre, 46 Allée d'Italie, 69364 Lyon Cedex 07, France
*Present address: Laboratoirc de Pétrologie Métamorphique, C.N.R.S., URA 736, Université de Paris 7, 4 Place Jussieu, F-75252 Paris Cedex 05, France.

Abstract: A T.E.M. study of omphacites from the western Italian Alps (Sesia Lanzo Zone and Monviso eclogites) has revealed a bimodal size distribution of antiphase domains: (a) 250–350 Å, (b) ≥ 2500 Å. In addition observed dislocation substructures and ‘large-scale’ antiphase domains are intimately interconnected.

A model is presented that can explain modification of the antiphase domain sizes by the interplay of cooling/growth and dislocation glide and/or creep mechanisms. Subsequent coarsening of the modified antiphase domains is inferred to be the result of surface free-energy processes. The model clearly illustrates that only the ‘relatively undeformed’ areas containing the small-scale antiphase domains can be used for thermometric methods.

Keywords: western Italian Alps • omphacite • antiphase domain • 1/2<110> dislocation

Mineralogical Magazine; September 1991 v. 55; no. 380; p. 397-407; DOI: 10.1180/minmag.1991.055.380.09
© 1991, The Mineralogical Society
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