Changes of microstructure, mineralogy, chemistry and anisotropic properties during progressive strain in the Kavala mylonitic shear zone (Rhodope Massif, NE Greece): advancement after a synergistic approach

Quantitative parameters associated to progressive mylonitic deformation are strictly controlled by several counterbalancing mechanisms competing with each other. In this view, synergistic quantitative investigation of relatively simple rocks characterized by a clear strain increment can aid to shed new light in the calculation of anisotropic properties driven by progressive grain size reduction and dynamic recrystallisation and/or by phase transformations and metamorphic reactions (e.g. reaction hardening/softening), which often provide a further softening process contributing to concentrate deformation. As an example, the Kavala shear zone, exposed in north-eastern Greece, has been chosen, where early-Miocene syn-extensional granodiorite emplacement occurred; here, relatively isotropic granodiorite gradually evolves towards mylonitic granodiorite, with evidence of NE-SW monotonous stretching lineation consistent with the elongation of the exposed pluton. Stepwise controlled procedure allowed us: i) selection of variably deformed granodiorite samples characterized by homogeneous protolith, as inferred by geochemical and petrographical investigation; ii) quantification of grain size reduction as well as minerochemical modification during progressive shear increase by means of statistical data handling of EDS X-ray maps via Principal- and Canonical-Component-Analysis; iii) investigation on shape and crystallographic preferred orientation of quartz-rich domains, which control the bulk-rock rheology during deformation, via image processing utilities; iv) determination of petrophysical properties at confining pressure in rocks characterized by progressive shear strain. Finally, results pointed out a close relationship between petrophysical properties and changes in microstructure and composition along the shear zone investigated.