New insights on volcanic activity related to the opening of the Central Tyrrhenian Sea: the transitional basalts of the Ventotene volcanic ridge (Pontine Islands, Italy).

High-resolution geophysical data and ROV dives collected along the eastern margin of the Tyrrhenian back-arc basin, in the Pontine Islands area, led to the exploration and mapping of the Ventotene Volcanic Ridge (VR; Cuffaro et al., 2016). The latter is a NW-SE-oriented, and partially buried morphological high, located 25 km north of Ventotene Is. (Eastern Pontine Islands, EPI), whose volcanic origin is linked to the local and regional fault patterns. The VR is considered part of the alignment of volcanoes developed the from NW to SE in the central-eastern area of Tyrrhenian Sea, from Western Pontine Islands (WPI) to Campanian Volcanic Region. Here we report the petrographic/geochemical (including Sr-Nd isotopes) and new 40Ar-39Ar age data of samples dredged along the VR in December 2015 from National Research Council Vessel Minerva Uno. We discuss the results in the light of tectonic setting of the VR, in the context of the extensional deformations related to the opening of the Tyrrhenian back-arc basin, which drove the magmatism from the WPI to the east Tyrrhenian margin during Plio-Pleistocene. The magmatism developed in the WPI cover a ?me span of 4.5-1.0 Ma and includes differentiated products of three distinct rock-series, namely, High Potassium-Calc Alkaline (HK-CA), Transitional (TR) and K-alkaline (KA). The parental products of HK-CA and KA series were mostly erupted eastward, in the Campania Plain subsoil (~2 Ma), and in the EPI up to Campania Plain (0.9 Ma to present), respectively. VR samples are basalt to trachybasalt belonging to the transitional-series and then suitable parental melts of the WPI transitional peralkaline rhyolites (1.6-1.1 Ma). This means that the 2.7 Ma age determined for VR basalts significantly enlarge the ?time interval of transitional magmas emplacement in the area. Moreover, a par?al temporal overlap between HK-CA (4.5-2.0 Ma) and transitional (2.7-1.1 Ma) magmatism occurs and an almost continuity with the KA rock-series ones (~1.0 Ma to present). Based also on geochemical signatures of VR samples, we suggest that between ~4.5 and ~2.0 Ma in the area between WPI through the central Tyrrhenian Sea (VR) up to the subsoil of Campi Flegrei a HK-CA/TR magmatism, with typical orogenic signatures originated from similar thought heterogeneous supra-subduction sources, due to crustal components variously recycled in the mantle via subduction. The change towards the more typical KA products with orogenic signatures, which started to erupt at Ponza Is. and continued south-eastwards through La Botte neck, the EPI up to Procida and Ischia Islands, is probably correlated with changes in regional tectonic activity in the area. Cuffaro M., Martorelli E., Bosman A., Conti A., Bigi S., Muccini F., Cocchi L., Ligi M., Bortoluzzi G., Scrocca D., Canese S., Chiocci F.L., Conte A.M., Doglioni C. & Perinelli C. 2016. The Ventotene Volcanic Ridge: a newly explored complex in the central Tyrrhenian Sea (Italy). Bull. Volcanol., 78:86.