Natural deformation and recrystallization of some intermediate plagioclase feldspars

Terkel Svava Olsen, David L. Kohlstedt

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Intermediate (An25-An48) plagioclase feldspars from the Nordre Strømfjord shear zone, central West Greenland, have undergone extensive ductile deformation by intracrystalline slip and by twinning. The plagioclases were deformed under low granulite facies conditions. Optical substructures include undulatory extinction, deformation bands, subgrains, and deformational twins, mainly on the albite law. Dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation (migration of a high-angle boundary) as a secondary mechanism. In some cases, recrystallization is accompanied by a small decrease in the An-content which is thought to indicate prograde metamorphic conditions. The plagioclases exhibit a good crystallographic preferred orientation which is compatible with (010) [001] being the principal slip system. Quartz has, in the same rocks, undergone more plastic deformation and more extensive recovery than plagioclase. This is, at least in part, due to the fact that most dislocations in plagioclase are dissociated.

Original languageEnglish (US)
Pages (from-to)107-131
Number of pages25
Issue number1-2
StatePublished - Jan 10 1985

Bibliographical note

Funding Information:
This paper has benefitted from valuable discussions with, and constructive criticism by, John M. Bird and Maura S. Weathers, Cornell University, and the two reviewers. The use of electron microscopes in the Materials Science Centre central facility at Cornell University is acknowledged. Mr. John Hunt, Cornell University assisted at the electron microprobe. Financial support from the Danish Natural Science Research Council through Grant 511-15360 (to TSO) and from the U.S. Geological Survey through Contract 14-08-001-19119( DLK) is gratefully acknowledged. Field work was sponsored by the Geological Survey of Greenland and we thank the Director of the Survey for permission to publish the paper.


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