New geochemical data on submarine volcanics from the Pontine Archipelago (Tyrrenian Sea, Italy)

In the framework of the spatial-temporal distribution and compositional variability of Plio-Quaternary magmatic products emplaced in the Tyrrhenian and surrounding regions, the magmatism of he Western Pontine Islands (WPI -Ponza, Zannone, Palmarola) is still matter of debate,due to the complex geological setting in which the islands formed. The magmatism of WPI offers the opportunity to investigate the origin of calcalkaline and alkaline-peralkaline magmas. in a complex basin undergoing extension within an overall collisional geodynamic setting. Previous studies defined that: 1) Pliocene volcanic episodes are represented by silica-rich, high-K calcalkaline volcanic units at Ponza and Zannone islands; 2) Pleistocene volcanic episodes are represented by intermediate to highly evolved (K-trachytes to peralkaline trachytes and rhyolites) shoshonitic rocks cropping out in SE Ponza and Palmarola islands. According to Conte & Dolfi (2002) the magmatism of WPI was related to magmas similar to the less evolved mafic-intermediate calcalkaline and shoshonitic magmas occurring nearby Campanian Volcanic District, which variously interacted with crustal materials. Other Authors proposed different scenarios, relating the WPI magmatism: i) to sources influenced by the change of geodynamic setting from subduction-related to intraplate (Cadoux et al., 2005) or ii) to the framework of the whole italian magmatism resulting by a mixture of a ~FOZO mantle component and minor upper crustal contamination (Cadoux et al., 2007). Paone (2013) emphasized the occurrence of widespread anatectic processes for Pliocene and Pleistocene rhyolites. In this contribution we present new data on dredged samples from the submarine part of the archipelago that extends the dataset currently available from subaerial rocks. Noteworthy, the new samples include relatively undifferentiated rocks (andesites, latites), which weren’t known in the WPI magmatic associations. In this framework, on the basis of new major/trace element and Sr-Nd isotopic data we propose that the WPI magmas formed in coherent subduction-related environment from mantle derived melts variously affected by crustal contamination during differentiation in shallow level magma chambers.