Concurrent leucite-free and leucite-bearing magmatism in the recent stages of activity (<305 ka) of the Roccamonfina volcano (Central-Southern Italy)

We report here the results of a petrological study of lava and pyroclastic products from the recent phase of activity of the Roccamonfina volcano, postdating the ca. 305 ka eruption of the White Trachytic Tuffs (WTT). Rocks mostly belong to a leucite-free low-K series (LKS), but also include products of a leucite-bearing high-K series (HKS). The latter is prominent during the early phases of the volcano activity (>350 ka, older than the Brown Leucitic Tuff or BLT eruption), for which subordinate LKS activity has also been recently recognised. This further emphasizes that the petrological evolution of the volcano was more complex than previously thought, with a more progressive HKS to LKS transition. Compared to their older counterparts, post-WTT HKS magmas are generally less silica-undersaturated, with leucite mostly in the groundmass instead of being a major phenocryst phase. Compositions range from potassic trachybasalt/basanite to phonolite and are generally lower in K2O (4.0-8.8 vs. 5.0-11.1 wt%), Rb (136-437 vs. 271-1196 ppm) and Sr (349-1240 vs. 156-2651 ppm) with respect to pre-BLT HKS basanite/tephrite-phonolite rocks. Primitive-mantle normalised spiderdiagrams for the least evolved HKS rocks of the two periods share the same subduction-related signature, but the post-WTT rocks have lower LILE/HFSE and LREE-MREE/HREE enrichments. Post-WTT LKS rocks range from basalt to (high-silica) trachyte and are mostly silica-saturated to slightly silica-oversaturated, whereas the few pre-BLT LKS rocks are weakly silica-undersaturated trachytes. Except for SiO2 (45.2-68.9 vs. 46.7-58.8 wt%) and K2O concentrations (1.20-7.26 wt%), post-WTT LKS magmas are distinguished from HKS magmas by very subtle compositional differences, the least evolved rock types of the former having slightly lower Th/Nb, LaN/YbN and DyN/YbN and slightly higher Ta/Nb. Isotope compositions for the post-WTT rocks define two main clusters, both more Sr-unradiogenic (87Sr/86Sr 0.70747-0.70862 and 0.70658-0.70737) and Nd-radiogenic (143Nd/144Nd 0.51223-0.51228 and 0.51236-0.51240) with respect to the pre-BLT magmas (0.70868-0.71019 and 0.51211-0.51224). Further, two samples from the HKS series make a third group with even lower 87Sr/86Sr (0.70652-0.70653) and higher 143Nd/144Nd (0.51250-0.51252). Our preliminary results suggest that several source components were likely involved during the recent phase of the Roccamonfina activity, possibly including also those that produced the magmas from the ancient phase of activity. Additional complexities have to be invoked in order to explain the concurrent generation of both leucite-bearing and leucite-free magma series.