Evidenze di slip prismatico in direzione c in una zona di shear granulitica. Evidence of primastic C-direction slip in a granulite shear zone.

In this work we analyze the microstructural deformation of a milonitic metapelite, from the Amaroni shear zone, in the Calabrian Serre Massif. This fault seems to be linked to the Curinga-Girifalco Lines, an Alpine contact (developed under greenschist facies condition) which separates the deepest high grades metamorphic basement from upper lower grade metamorphic domains. This research aims to discover if there is a relationship between the two faults, or if they are completely independent of each other. Specifically, we would like to understand if the milonite was subject to granulite metamorphic facies condition (high temperature), typical of the older Varisican Orogeny, or if it formed at lower temperatures during greenshist/amphibolite facies condition and therefore during a later time. These metamorphic condition can be deduced from the analysis of the microstructures of the rocks, specifically from the crystallographic preferred orientation (CPO) of quartz. The EBSD technique we used enables the measurement of the crystallographic preferred orientation of any single rock-forming mineral. Our analytical data show that during milonite formation, quartz deformed by prism <c> glide, which is indicative for high temperature condition, typically of the granulite facies. These condition were only achieved in a time interval between 300 and 250 Ma, i.e. during the extension phase of the Varisican Orogeny, or immediately after.