From ocean to subduction: the polyphase metamorphic evolution of the Frido Unit metadolerite dikes (Southern Apennine, Italy)

Maria T. Cristi Sansone, Paola Tartarotti, Giovanna Rizzo, and Giacomo Prosser

The Liguride accretionary wedge in the Southern Apennine chain includes ophiolitic slices representing remnants of the Jurassic Tethyan ocean. In the northeastern slope of the Pollino Ridge (Calabria-Lucania border zone) ophiolitic rocks mostly consist of serpentinites crosscut by metadolerite dikes showing different types of textures, ranging from magmatic intersertal/intergranular and blastophitic to mylonitic and cataclastic. The metadolerite dikes 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 history, from the emplacement in the Jurassic western Tethys to the subsequent evolution in the Apennine accretionary wedge, is traced by pseudomorphic and coronitic textures of amphibole replacing igneous clinopyroxene. More specifically, this is attested to by the occurrence of brown amphibole coronas 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 metadolerites are almost unaffected by high strain zones 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.