Microstructural Investigation of Naturally Deformed Leucogneiss from an Alpine Shear Zone (Southern Calabria – Italy) ROSOLINO CIRRINCIONE,EUGENIO FAZIO,PATRIZIA FIANNACCA,GAETANO ORTOLANO, and ROSALDA PUNTURO Abstract—In order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain, a suite of deformed leucogneiss collected within a ductile shear zone outcropping in Calabria (southern Italy) was investigated. Based on the microstructural approach and matrix-clast relationships, the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks. Accordingly, quartz c-axis orientation patterns were determined by image-assisted analysis. Results revealed a correlation between finite strain and textural features: As strain increases, the matrix develops at the expense of the clast counterpart, which is instead progressively reduced in both size and amount. Key words: Textural anisotropy, quartz c-axis pattern, bulk rock rheology, shear-zone, mylonite. 1. Introduction Shear zones are particular tectonic settings in which strain is located within the Earth’s crust. They act as preferential pathways accommodating the deformation which accumulates on a geological time scale in response to plate tectonics and, at the same time, operate as efficient systems in both exhumation and burial processes during orogenic phases. Due to their geological and structural significance, shear zones play an important role in geodynamic reconstructions, since they are important environments for understanding crustal rheology. As progressive deformation continues, rocks show rheological behaviour varying in time and space, and their textures may thus furnish important insights on the dependence of rock properties with varying intensive parameters such as temperature, confining pressure, strain gradient, etc. Recent enhanced knowledge (CHRISTIANSEN and POLLARD, 1997;STIPP et al., 2002; HEILBRONNER and TULLIS, 2006;KURZ and NORTHRUP, 2008), not only of microstructural deformation mechanisms but also better definition of the flow laws that control the rheological behaviour of mineral phases in varying conditions (e.g., strain rate, Department of Geological Sciences, University of Catania, Corso Italia 57, I-95129 Catania, Italy. E-mail: punturo@unict.it Pure appl. geophys. 166 (2009) 995–1010 Ó Birkha ¨user Verlag, Basel, 2009 0033–4553/09/050995–16 DOI 10.1007/s00024-009-0483-4 Pure and Applied Geophysics