Southern Tyrrhenian Sea

Abstract

The Southern Tyrrhenian seafloor (south of the 41° Parallel line) hosts a large number of Miocene to Quaternary volcanoes ranging in composition from MORB- to OIB- and arc-type. MORB-type rocks are concentrated in the Vavilov Basin, but their role is evident for other Tyrrhenian Sea volcanoes. OIB-type components similar to Etna and Ustica (FOZO) are better shown by the Prometeo lava field (SE of Ustica Island) and by a single sample from the Marsili Seamount. A distinct OIB-type composition, similar to Sardinia Plio-Quaternary magmas, is found for a few rocks collected offshore eastern Sardinia. Subduction-type rocks are widely distributed throughout the Tyrrhenian Sea basin, from the Upper Miocene potassic alkaline Cornacya volcano (offshore southeastern Sardinia) to the tholeiitic, calcalkaline and shoshonitic seamounts in the central Tyrrhenian Sea and the Aeolian area. The wide variety of rock types reveals a highly heterogeneous upper mantle in the Southern Tyrrhenian Sea. Such extreme heterogeneity is debated. Most authors agree that the Tyrrhenian Sea represents a back-arc basin where melting of various mantle rocks (ancient lithosphere, passively ascending asthenosphere, and mantle rocks inflown from the foreland) is responsible for the generation of MORB- and OIB-type magmas. Arc-type magmatism would be related to the release of fluids by the Ionian subduction systems that migrated south-eastward contemporaneously with the opening of the Southern Tyrrhenian Sea.