CRUST AND UPPER-MANTLE MODELS ALONG THE ACTIVE TYRRHENIAN RIM

The volcanic complexes from the Eolian islands to the Campania/Roman r egions and Tuscany further north, rest on lithospheric sectors which o verlie the Adriatic continental lithosphere sinking along the Apennine -Maghrebian orogenic belt. Evidence for this stems from the melting, a t mantle depth, of upper crustal materials as indicated by the widespr ead interaction of S-type and K-alkaline melts. The genesis of atypica l magmas of the Roman Province (central-southern Italy) appears to be the result of an important block faulting and deep lithospheric riftin g of the Apennine continental margin lying parallel to and above relic sinking slabs. Intermediate and deep-focus earthquakes indicate that the lithospheric slab is still seismically active under the Eolian-Cal abrian area and, sporadically, at the southern end of Campania. On the other hand, in the Roman/Tuscan region, it seems to be almost inactiv e, few earthquakes having been located with hypocentral depths not exc eeding 150 km. The analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shorteni ng in correspondence of Tuscany and South Tyrrhenian sea, which are se parated by a tensional region, which extends from Latium to Calabria. The existence of distinct lithospheric slabs along the Tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as P-wave residuals, and is confirmed by the trend of long-wavel ength gravity anomalies. Bidimensional gravity models along transects in the Tyrrhenian sea and italian peninsula interpreted within the geo metrical constraints imposed by the results of the interpretation of a eromagnetic, seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above-mentioned lithospheri c slabs.