The interplay and effects of deformation and crystallized melt on the rheology of the lower continental crust,Fiordland, New Zealand |
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| Institution: | 1. Université de Montpellier 2, CNRS, UMR 5342 Geosciences Montpellier, 34095 Montpellier, France;2. Université Lille 1, CNRS, UMR 8207 Unité Matériaux et Transformation, 59555 Villeneuve d''Ascq, France |
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| Abstract: | Microstructural, electron backscatter diffraction (EBSD), and misorientation analyses of a migmatitic granulite-facies orthogneiss from the exhumed lower crust of a Cretaceous continental arc in Fiordland, New Zealand show how deformation was accommodated during and after episodes of melt infiltration and high-grade metamorphism. Microstructures in garnet, omphacite, plagioclase, and K-feldspar suggest that an early stage of deformation was achieved by dislocation creep of omphacite and plagioclase, with subsequent deformation becoming partitioned into plagioclase. Continued deformation after melt infiltration resulted in strain localization in the leucosome of the migmatite, where a change of plagioclase deformation mechanism promoted the onset of grain boundary sliding, most likely accommodated by diffusion creep, in fine recrystallized plagioclase grains. Our results suggest three distinctive transitions in the rheology of the lower crust of this continental arc, where initial weakening was primarily achieved by deformation of both omphacite and plagioclase. Subsequent strain localization in plagioclase of the leucosome indicates that the zones of former melt are weaker than the restite, and that changes in deformation mechanisms within plagioclase, and an evolution of its strength, primarily control the rheology of the lower crust during and after episodes of melting and magma addition. |
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| Keywords: | Electron backscatter diffraction Migmatite Plagioclase Lower crust rheology Fiordland |
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