Thermal structure of the shallow upper mantle beneath Italy and neighbouring areas: Correlation with magmatic activity and geodynamic significance

Using an advanced seismic velocity–temperature conversion technique, we infer the temperature and melt distribution in the uppermantle (down to 300 km) beneath Italy and surroundings, starting from absolute S-wave velocity models. The presence of melt, indicated by the seismic reconstruction of the mantle structure in the Tyrrhenian Sea area, requires an extension of the standard conversion procedure to allow for a correction of seismic velocities for the effect of hydrous melt occurrence. The thermal structure of the upper mantle along four sections crossing the Tyrrhenian basin and the Italian peninsula is investigated. Some characteristics of the obtained thermal structures and melt distributions are well delineated and in accordance with recent models of the evolution of the Tyrrhenian Sea area. The negative thermal anomalies observed in all sections clearly delineate the subduction process of the Adriatic plate (beneath Umbria, Calabria and the Aeolian arc), or the episode of post-continental convergence (beneath Tuscany), or the thermal effect of the remnant of the Adriatic plate (Campania). Temperature values at Moho seem to be generally correlated with surface heat flow determinations in the Tyrrhenian Sea area and surroundings, although most sectors of the study area (like Tuscan–Tyrrhenian area, Apennines and Adriatic trough) have not yet reached the steady-state thermal regime. The thermal gradients evaluated in the Adria foreland are high in comparison with those of the back-arc area (Tyrrhenian Sea) and could be an effect of the eastward mantle flow beneath Adria lithosphere or a result of the presence of low fraction of melts ≤1 wt.%, which cannot rise in compressive regimes, or both. The melt fraction distribution obtained by the conversion procedure is approximately correlated with the age of the magmatism, the highest abundance occurring in the southern Tyrrhenian Sea, in accordance with widespread active volcanism in this area.