Crystallographic preferred orientations and microstructure of a Variscan marble mylonite in the Ossa-Morena Zone (SW Iberia)

Abstract

The mylonitic marbles of the Cherneca shear zone, a Variscan sinistral strike-slip structure developed in the Ossa-Morena Zone (SW Iberia) related to the emplacement of the Santa Olalla Igneous Complex, were studied in detail. Different mylonites (from protomylonites to ultramylonites) were analyzed by Electron Back-Scattering Diffraction (EBSD) in order to determine the crystallographic preferred orientation (CPO) of calcite. The CPOs show very good agreement with experimental torsion work giving suitable interpretations of the operative slip systems and strain quantifications, thus the obtained natural CPOs validate the experimental approaches. A wide range of observed textures and microstructures are mainly controlled by the amount of shear strain, the presence of secondary phases, and the development of antithetic subsidiary shears. The effect of secondary phases and the nucleation of antithetic shear bands on texture development are discussed.