Conclusions
The metadolerites from the Frido Unit have been affected by ocean-floor metamorphism under amphibolite to greenschists facies conditions. Subsequent subduction-related metamorphism under relatively HP/LT (blueschist facies) conditions affected the rocks during the formation of the Apennine accretionary prism. Late orogenic minerals of the prehnite-pumpellyite facies have crystallized in rocks and in veins. Such long-lasting metamorphic evolution accompanying the rocks investigated here, from their emplacement in the Jurassic western Tethys to the tectonic history in the Apennine accretionary wedge, is easily readable within microstructural domains characterized by pseudomorphic textures. The zoned structure of amphiboles replacing igneous clinopyroxene records the entire metamorphic evolution, as attested by the occurrence of Ca-amphiboles (brown amphibole rimmed by green and blue-green to pale-green amphiboles) that are statically replaced by Ca-Na-amphibole and subsequent Na-amphibole. The investigated textural domains still record such a long-lasting metamorphic evolution since the rock was relatively unaffected by high strain zones (undeformed pods), due to deformation partitioning in the weaker serpentinite matrix or in low-grade metasediments during oceanic lithospheric stretching or during emplacement in the accretionary wedge.