Microstructural and textural modification of columnar calcite under increasing shear strain (Evia Island, Greece)

Abstract

We studied the microstructural and textural modification of columnar calcite naturally deformed at increasing shear strain. The studied marbles were sampled from different structural levels of the Basal Unit of the Cycladic Massif on Evia Island, Greece. The marbles have experienced high pressure metamorphism at peak temperatures around 350 °C. The long axes of the columnar calcite grains and their c-axes were originally oriented normal to the foliation and were subsequently rotated during exhumation. The obliquity of the long axes of relict calcite grains with respect to the foliation was used to infer shear strain. Electron backscatter diffraction (EBSD) analysis was used to characterize the marble microstructure as well as the crystallographic preferred orientations (CPO) and misorientations in calcite. Recrystallization of calcite was active from very low shear strains (0.1) and mylonitization (∼60% area fraction of recrystallized grains) took place at shear strains >∼4. Subgrain rotation was the dominant recrystallization mechanism in calcite in all samples. Differential stress and strain rate did not show any systematic variation with increasing shear strain. A shear strain of up to ∼4 was not enough to produce a strong CPO in calcite.