Dynamic recrystallization of garnet and related diffusion processes

Autor(en)

M Bestmann, Gerlinde Habler, F Heidelbach, Martin Thöni

Abstrakt

Electron backscatter diffraction and compositional data of Permian metapegmatite garnet from the

Koralpe basement (Eastern Alps, Austria) show the evolution of distinct intracrystalline shear zones in

c. 10 mm sized almandine¿spessartine garnet. Orientation maps reveal continuous distortion of the crystal

lattice. New garnet grains (grain size 20¿30 mm) within intragranular deformation zones, oriented

subparallel to the main foliation of the metapegmatite, have similar crystal orientations to the host garnet,

whereas recrystallized grains along fractures or along growth heterogeneities show a much weaker

crystallographic preferred orientation (CPO). Needles of kyanite as well as inclusions of apatite, xenotime

and rutile occur along the deformation zones. Together with the Ca variation across the deformation

zones these inclusions give evidence of material diffusion related to crystal plastic deformation of garnet.

The individual garnet porphyroclasts record the evolution of recrystallization microfabrics. New grains,

once formed by subgrain rotation recrystallization, are able to deform partly by diffusion accommodated

grain boundary sliding resulting in a weakening of the CPO. Whereas magmatic garnet growth had taken

place at LP conditions in equilibrium with andalusite, the occurrence of kyanite in some deformation

zones, triggered by the localized crystal plasticity of garnet, indicates that the deformation was related

to the Cretaceous HP metamorphic event.

Organisation(en)

Department für Lithosphärenforschung

Externe Organisation(en)

Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Universität Bayreuth

Journal

Journal of Structural Geology

Band

30

Seiten

777-790

Anzahl der Seiten

14

ISSN

0191-8141

Publikationsdatum

2008

Peer-reviewed

Ja

ÖFOS 2012

105124 Tektonik, 105116 Mineralogie, 1051 Geologie, Mineralogie

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