Recent petrological studies on the Axial Zone of the Variscan chain have revealed the occurrence of anticlockwise P-T trajectories in metamorphic rocks from Corsica and Sardinia. These new findings, at first glance, appears to be in contrast with the clockwise P-T paths classically described for several high-pressure metamorphic rocks from the Variscan Sardinia - Corsica block in the last decades. For the first time in Variscan Corsica, Massonne et al. (2018) described the anticlockwise P-T path of micaschists from the Porto Vecchio region. These rocks underwent prograde metamorphism starting at 3 kbar/600°C and then reached peak metamorphic conditions at 7 kbar/600-630°C. The Porto Vecchio micaschists are bordered to the north by the Solenzara-Fautea metamorphic rock unit that is, in turn, characterized by migmatites and granulites that underwent a clockwise P-T loop related to burial of continental crust to high-pressure (1.8–1.4 GPa) followed by high- to ultrahigh-temperature conditions (900–1000 °C; Giacomini et al., 2008). New, preliminary results on these rocks reveal that these latter peak temperatures could be probably significantly lower than those above mentioned, but there is no doubt about the clockwise shape of their P-T path. In the neighbouring Variscan terrains of north-eastern Sardinia, Scodina et al. (2019) reconstructed the P-T history of an amphibolite body whose burial path started at 0.8 GPa and was then followed by a slight increase in temperature up to peak metamorphic conditions of 1.3–1.4 GPa/690–740 °C. These amphibolites are hosted by migmatites for which a clockwise P-T path, related to a nearly isothermal exhumation, is widely accepted in the literature and confirmed by the most recent studies (Massonne et al., 2013 and references therein). In conclusion, it thus appears that during the Variscan collision, rock slices of different crustal levels were brought together and metamorphic rocks from upper and lower plates were involved in a particle path along an exhumation channel. Giacomini F., Dallai L., Carminati E., Tiepolo M. & Ghezzo C. 2008. Exhumation of a Variscan orogenic complex: Insights into the composite granulitic–amphibolitic metamorphic basement of southeast Corsica (France).J. Metam. Geol., 26, 403–436. Massonne H.-J., Cruciani G. & Franceschelli M. 2013. Geothermobarometry on anatectic melts - a high-pressure Variscan migmatite from northeast Sardinia. Int. Geol. Rev., 55, 1490–1505. Massonne H.-J., Cruciani G., Franceschelli M. & Musumeci G. 2018. Anticlockwise pressure–temperature paths record Variscan upper-plate exhumation: example from micaschists of the Porto Vecchio region, Corsica. J. Metam. Geol., 36, 55–77. Scodina M., Cruciani G., Franceschelli M. & Massonne H.-J. 2019. Anticlockwise P-T evolution of amphibolites from NE Sardinia, Italy: geodynamic implications for the tectonic evolution of the Variscan Corsica-Sardinia block. Lithos, 324–325, 763–775.
Clockwise and anticlockwise P-T path in the axial zone of the Variscan Sardinia-Corsica block
Franceschelli M.;Cruciani G.
2019-01-01
Abstract
Recent petrological studies on the Axial Zone of the Variscan chain have revealed the occurrence of anticlockwise P-T trajectories in metamorphic rocks from Corsica and Sardinia. These new findings, at first glance, appears to be in contrast with the clockwise P-T paths classically described for several high-pressure metamorphic rocks from the Variscan Sardinia - Corsica block in the last decades. For the first time in Variscan Corsica, Massonne et al. (2018) described the anticlockwise P-T path of micaschists from the Porto Vecchio region. These rocks underwent prograde metamorphism starting at 3 kbar/600°C and then reached peak metamorphic conditions at 7 kbar/600-630°C. The Porto Vecchio micaschists are bordered to the north by the Solenzara-Fautea metamorphic rock unit that is, in turn, characterized by migmatites and granulites that underwent a clockwise P-T loop related to burial of continental crust to high-pressure (1.8–1.4 GPa) followed by high- to ultrahigh-temperature conditions (900–1000 °C; Giacomini et al., 2008). New, preliminary results on these rocks reveal that these latter peak temperatures could be probably significantly lower than those above mentioned, but there is no doubt about the clockwise shape of their P-T path. In the neighbouring Variscan terrains of north-eastern Sardinia, Scodina et al. (2019) reconstructed the P-T history of an amphibolite body whose burial path started at 0.8 GPa and was then followed by a slight increase in temperature up to peak metamorphic conditions of 1.3–1.4 GPa/690–740 °C. These amphibolites are hosted by migmatites for which a clockwise P-T path, related to a nearly isothermal exhumation, is widely accepted in the literature and confirmed by the most recent studies (Massonne et al., 2013 and references therein). In conclusion, it thus appears that during the Variscan collision, rock slices of different crustal levels were brought together and metamorphic rocks from upper and lower plates were involved in a particle path along an exhumation channel. Giacomini F., Dallai L., Carminati E., Tiepolo M. & Ghezzo C. 2008. Exhumation of a Variscan orogenic complex: Insights into the composite granulitic–amphibolitic metamorphic basement of southeast Corsica (France).J. Metam. Geol., 26, 403–436. Massonne H.-J., Cruciani G. & Franceschelli M. 2013. Geothermobarometry on anatectic melts - a high-pressure Variscan migmatite from northeast Sardinia. Int. Geol. Rev., 55, 1490–1505. Massonne H.-J., Cruciani G., Franceschelli M. & Musumeci G. 2018. Anticlockwise pressure–temperature paths record Variscan upper-plate exhumation: example from micaschists of the Porto Vecchio region, Corsica. J. Metam. Geol., 36, 55–77. Scodina M., Cruciani G., Franceschelli M. & Massonne H.-J. 2019. Anticlockwise P-T evolution of amphibolites from NE Sardinia, Italy: geodynamic implications for the tectonic evolution of the Variscan Corsica-Sardinia block. Lithos, 324–325, 763–775.
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