P–T–t path of the Hercynian low-pressure rocks from the Mandatoriccio complex (Sila Massif, Calabria, Italy): new insights for crustal evolution

The tectono-metamorphic evolution of the Hercynian intermediate-upper crust outcropping in eastern Sila (Calabria, Italy) has been reconstructed, integrating microstructural analysis, P-T pseudosections, mineral isopleths and geochronological data. The studied rocks belong to a nearly complete crustal section that comprises granulite facies metamorphic rocks at the base and granitoids in the intermediate levels. Clockwise P-T paths have been constrained for metapelites of the basal level of the intermediate-upper crust (Umbriatico area). These rocks show noticeable porphyroblastic textures documenting the progressive change from medium-P metamorphic assemblages (garnet-and staurolite-bearing assemblages) towards low-P/high-T metamorphic assemblages (fibrolite- and cordierite-bearing assemblages). Peak-metamorphic conditions of similar to 590 degrees C and 0.35 GPa are estimated by integrating microstructural observations with P-T pseudosections calculated for bulk-rock and reaction-domain compositions. The top level of the intermediate-upper crust (Campana area) recorded only the major heating phase at low-P (similar to 550 degrees C and 0.25 GPa), as documented by the static growth of biotite spots and of cordierite and andalusite porphyroblasts in metapelites. In situ U-Th-Pb dating of monazite from schists containing low-P/high-T metamorphic assemblages gave a weighted mean U-Pb concordia age of 299 +/- 3 Ma, which has been interpreted as the timing of peak metamorphism. In the framework of the whole Hercynian crustal section the peak of low-P/high-T metamorphism in the intermediate-to-upper crust took place concurrently with granulite facies metamorphism in the lower crust and with emplacement of the granitoids in the intermediate levels. In addition, decompression is a distinctive trait of the P-T evolution both in the lower and upper crust. It is proposed that post-collisional extension, together with exhumation, is the most suitable tectonic setting in which magmatic and metamorphic processes can be active simultaneously in different levels of the continental crust.