P-T-t path of yhe 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 assem- blages) towards low-P ⁄ high-T metamorphic assemblages (fibrolite- and cordierite-bearing assemblages). Peak-metamorphic conditions of ∼ 590 °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 (∼550 °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.