Dry high-temperature shearing in the fossil Hercynian lower crust of Calabria (southern Italy)

In the Hercynian lower crust of Calabria, post-Hercynian shearing occurred during retrograde amphibolite to sub-greenschist facies conditions and was localised in mm to cm thick shear zones. With the aid of (i) petrological and microstructure-based thermobarometry, (ii) textural analyses, and (iii) infra-red spectroscopy, the timing, P-T conditions and kinematics of shearing are exemplified. ( 1) The general top-to-the-NW transport of the lower crustal section is reflected by the shear zone. (2) A period of annealing is bracketed by a stage of high-temperature and one of low-temperature shearing. (3) Even in ultramylonitic layers and in the greenschist facies, shearing occurred in dry conditions. (4) The shear zone was active for approximately 60 million years. (5) After the first formation of a shear zone, the concentration and continuation of movements was not necessarily governed by the infiltration of fluids but by the presence of a texturally weak zone. (6) Despite the general problems of exchange-reaction-based thermobarometry in shear zones, in specific cases like the one presented here reliable results may be