The inner Northern Apennines belt (i.e., northern Tyrrhenian Sea and Tuscany) is an Alpine chain affectedby high-P metamorphic conditions during its evolution. Although Elba Island is structurally located closeto the Adria-Europe suture zone, for several authors it represents a sector of the orogen affected bylow-P metamorphism. The involvement of Elba Island tectonic units in high-P metamorphism was onlysuspected for the sparse presence of phengitic white mica in the metasedimentary rocks. This paperpresents the first clear evidence of high-P and low-T metamorphism found in metabasite rocks embed-ded in the Cretaceous calcschist of eastern Elba Island. Mineral composition of metabasite includesGln + Cpx + Ep + Ab + Act + Qtz + Ilm ± Ti-oxide ± Spn and is indicative of a former equilibration in the epi-dote blueschist subfacies and subsequent retrogression in the greenschist facies. Recorded metamorphicconditions are P = 0.9–1.0 GPa and T = 330–350◦C. Tectonic discrimination using immobile elements inthe metabasite does not point to an oceanic setting. As a consequence, the metasedimentary succes-sion containing metabasite is explained as belonging to the Tuscan continental domain and not to theLigurian-Piedmont Ocean, as previously interpreted. Our results have two significant implications: (i)it is confirmed and strengthened that the tectonic stacking of the Elba Island units did not occur in alow-pressure context; (ii) Elba Island is now completely reconciled in the tectonic and metamorphicevolution of the inner Northern Apennines.

HP-LT metamorphism in Elba Island: Implications for the geodynamic evolution of the inner Northern Apennines (Italy)

BIANCO, CATERINA;Brogi, Andrea;CAGGIANELLI, Alfredo;LIOTTA, Domenico;
2015-01-01

Abstract

The inner Northern Apennines belt (i.e., northern Tyrrhenian Sea and Tuscany) is an Alpine chain affectedby high-P metamorphic conditions during its evolution. Although Elba Island is structurally located closeto the Adria-Europe suture zone, for several authors it represents a sector of the orogen affected bylow-P metamorphism. The involvement of Elba Island tectonic units in high-P metamorphism was onlysuspected for the sparse presence of phengitic white mica in the metasedimentary rocks. This paperpresents the first clear evidence of high-P and low-T metamorphism found in metabasite rocks embed-ded in the Cretaceous calcschist of eastern Elba Island. Mineral composition of metabasite includesGln + Cpx + Ep + Ab + Act + Qtz + Ilm ± Ti-oxide ± Spn and is indicative of a former equilibration in the epi-dote blueschist subfacies and subsequent retrogression in the greenschist facies. Recorded metamorphicconditions are P = 0.9–1.0 GPa and T = 330–350◦C. Tectonic discrimination using immobile elements inthe metabasite does not point to an oceanic setting. As a consequence, the metasedimentary succes-sion containing metabasite is explained as belonging to the Tuscan continental domain and not to theLigurian-Piedmont Ocean, as previously interpreted. Our results have two significant implications: (i)it is confirmed and strengthened that the tectonic stacking of the Elba Island units did not occur in alow-pressure context; (ii) Elba Island is now completely reconciled in the tectonic and metamorphicevolution of the inner Northern Apennines.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11586/140823
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