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The behaviour of submicron inclusions during host deformation

Autoren:Griffiths, ThomasHabler, GerlindeAbart, RainerRhede, Diether (Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum)
Abstrakt:Both brittle and plastic deformation strongly influence the location, rates and mechanisms of material transport in the earth’s interior. Mineral reactions and diffusion can be controlled by deformation, but in turn contribute to its localisation. We investigate the mechanisms of interaction between deformation and chemical reaction in the context of re-equilibration of inclusions in a deforming host mineral.Permian pegmatite garnets from the Koralpe, eastern Alps, contain numerous submicron sized inclusions. The pegmatitic assemblage was affected by deformation under eclogite facies conditions during the Cretaceous tectono-metamorphic event. The meta-pegmatite garnet deformed crystal-plastically at this metamorphic stage [1].Trails of inclusions crosscutting the garnet have a coarser grain size (1-10µm Ø) than inclusions outside the trails. In 10-40µm wide zones flanking the inclusion trails the original < 1µm sized inclusions are absent, defining bleaching zones.FEG-microprobe data showed that it is possible to form the microstructure isochemically. However, some trails were also found where inclusions have coarsened non-isochemically. In both cases no change in garnet major element composition was observed.From their microstructural characteristics it is inferred that the trails formed at sites of healed brittle cracks. Garnet deformation has been mapped using EBSD and correlates with re-equilibration microstructures. Bleaching zones are associated with systematic very low angle lattice rotations of garnet. Additionally, lattice rotations of up to 10˚ occurred adjacent to already coarsened inclusions.The new microstructural, microchemical and textural data document several different interactions between material transport, crystallization and deformation processes which contribute to the final microstructure. TEM investigations provide the opportunity to examine the types of defects present in order to help determine the mechanisms through which chemical and mechanical processes have interacted on the nanoscale.
Anzahl der Seiten:1
Journal Titel:Mineralogical Magazine
Publikations Typ:Meeting Abstract/Conference Paper
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