This study investigates the microstructure and texture variations across a mm-scale shear zone in Carrara marble of the Alpi Apuane (Italy). The microstructures have been investigated for grain size, texture, and shape fabrics. Textures have been measured with Computer-Integrated Polarization Microscopy (CIP) and Electron Back Scattered Diffraction (EBSD) separating porphyroclast and recrystallized grains. The deformation, which post-dates an earlier deformation phase and subsequent annealing, is strongly localized. The microstructures and textures change across the shear strain gradient and are interpreted to preserve a time sequence of progressive stages of deformation. The bulk shear strain rate is estimated to be about 1011 sec1 at deformation temperatures of approximately 325 C 30 C. The protomylonite is characterized by a core mantle structure with a bimodal grain size distribution which changes gradually to a completely dynamically recrystallized microstructure with a unimodal grain size distribution in the mylonitic center of the shear zone. Core-mantlestructures are produced by dominant rotation recrystallization accompanied by some grain boundary migration. The microstructural transition from protomylonite to mylonite coincides with a change in texture. With increasing strain the single c-axis maximum of an earlier inherited texture in the protomylonite is replaced by a similar texture in a different orientation (maximum normal to the shear plane) which is consistent with dominant basal hai and r h2201i slip. The microstructural and textural variations depend on the proportion of recrystallized grains. As dynamic recrystallization progresses with finite strain the texture development is finite strain-dependent. The comparison of the microstructures and textures to other natural and to experimental examples explains the progressive change of the texture and demonstrates the texture evolution produced by dynamic recrystallization.
Strain dependent variation of microstructure and texture in naturally deformed Carrara marble
MOLLI, GIANCARLO
2007-01-01
Abstract
This study investigates the microstructure and texture variations across a mm-scale shear zone in Carrara marble of the Alpi Apuane (Italy). The microstructures have been investigated for grain size, texture, and shape fabrics. Textures have been measured with Computer-Integrated Polarization Microscopy (CIP) and Electron Back Scattered Diffraction (EBSD) separating porphyroclast and recrystallized grains. The deformation, which post-dates an earlier deformation phase and subsequent annealing, is strongly localized. The microstructures and textures change across the shear strain gradient and are interpreted to preserve a time sequence of progressive stages of deformation. The bulk shear strain rate is estimated to be about 1011 sec1 at deformation temperatures of approximately 325 C 30 C. The protomylonite is characterized by a core mantle structure with a bimodal grain size distribution which changes gradually to a completely dynamically recrystallized microstructure with a unimodal grain size distribution in the mylonitic center of the shear zone. Core-mantlestructures are produced by dominant rotation recrystallization accompanied by some grain boundary migration. The microstructural transition from protomylonite to mylonite coincides with a change in texture. With increasing strain the single c-axis maximum of an earlier inherited texture in the protomylonite is replaced by a similar texture in a different orientation (maximum normal to the shear plane) which is consistent with dominant basal hai and r h2201i slip. The microstructural and textural variations depend on the proportion of recrystallized grains. As dynamic recrystallization progresses with finite strain the texture development is finite strain-dependent. The comparison of the microstructures and textures to other natural and to experimental examples explains the progressive change of the texture and demonstrates the texture evolution produced by dynamic recrystallization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
