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The Strait of Sicily Rift Zone (SSRZ) is a northwest-southeast trending transtensional rift situated in the Mediterranean Sea between Sicily and north Africa. The SSRZ consists of three basins: the Pantelleria Trough, the Linosa Basin, and the Malta Trough. Volcanoes are situated in or adjacent to all except the Malta Trough, and include two islands (Pantelleria and Linosa) and several seamounts. The thickness of the crust throughout the region is 25-35 km, but thins to 16-18 km in the basins of the SSRZ. The Pantelleria Trough is characterized by high average heat flow values and a strong positive Bourger anomaly, which suggest assthenospheric upwelling to ~60 km and the presence of abundant basaltic material at depth. Mafic lavas ranging in composition from alkaline and transitional basalt to hawaiite (~45-50 wt% SiO2) comprise the dominant volume of eruptive products in the SSRZ; evolved rocks (trachyte and pantellerite) and common only on Pantelleria, where they crop out over ~94% of the island’s surface. Mafic lavas on Pantelleria are also the most evolved with Mg# ≤ 58, Ni ≤ 98 ppm, and Cr ≤ 183 ppm; more primitive mafic lavas can be found forming the seamounts (Mg# ≤ 67, Ni ≤ 280 ppm, and Cr ≤ 391 ppm) and cropping out on the island of Linosa (Mg# ≤ 71, Ni ≤ 409 ppm, and Cr ≤ 674 ppm) . There are two distinct mafic series on Pantelleria: a generally older (>50 ka) High Ti-P series (“Paleo-Pantelleria”), characterized by TiO2 > 3.0, P2O5 > 0.9, and high REE ratios; and a generally younger (

A general geochemical study comprehensive of major elements, trace elements and Sr-Nd isotopes in the bulk rock, coupled to noble gases analyses from fluid inclusions retained in minerals, was performed. The studied samples ( basalts, trachybasalts and basanites) represent some among the most primitive products of Etnean history. The variable composition measured in trace elements (i.e. Zr/Nb=2.81–4.98, Ce/Yb=35.02–66.90, La/Yb=15.36–35.52, Th/Y=0.17–0.43) was modeled as due to varying degrees of melting of a common mantle source. We numerically simulated the process by MELTS code to calculate a melting percentage for each product, and we accordingly estimated the pristine trace-elements content of their mantle source. This latter resulted to be common to all of the investigated samples and evidenced a close affinity between Etnean and Hyblean mantle. The observed coupling between trace elements and noble gases allow us to better define the Etnean mantle, which is compatible with a peridotitic matrix veined by 10% of clinopyroxenites. The geochemistry of the Sr-Nd-He isotopes (87Sr/86Sr= 0.703321–0.703910, 143Nd/144Nd= 0.512836 – 0.512913 and 3He/4He= 6.7–7.6 Ra), evidence also that crustal-derived fluids contaminated at various degrees the inferred source (?) The 87Sr/86Sr enrichment appears correlated to estimated degree of melting for each product, therefore the metasomatic fluids probably refertilized some portions of the mantle prior to partial melting. In contrast, the observed decoupling between 3He/4He and 87Sr/86Sr ratios could be related to shallower processes, due to magma aging or to a contribution of shallow fluids, responsible of the more radiogenic values of 3He/4He.

We carried out a geochemical investigation of the mantle beneath Hyblean and Etnean area through ultramafic xenoliths (peridotites and pyroxenites) retained in Miocenic age Hyblean volcanics and primitive Etnean lavas and tephra, respectively. Major and trace elements and Sr-Nd isotopes (whole rock and /or minerals) were analysed together with noble gases entrapped in fluid inclusions hosted in olivines and pyroxenes phenocrysts. The geochemical results from Hyblean xenoliths study highlighted the presence of two distinct compositional groups: the peridotites, featured by a more enriched geochemical fingerprint (3He/4He ∼7 Ra, 143Nd/144Nd ∼0.5129 and Zr/Nb ∼ 4) whereas the pyroxenites, characterized by a more primitive character (3He/4He up to 7.6 Ra, 143Nd/144Nd ∼0.5130 and Zr/Nb ∼30). Our interpretation is that metasomatic processes interested the Hyblean lithosphere and the pyroxenites (former primitive mantle melts) represent the metasomatizing agent. During their ascent these primitive melts permeated the peridotitic mantle at different levels, producing a variable degree of refertilization. The metasomatic processes affected distributions of both trace elements and noble gases, even though these geochemical tracers displayed very different sensitivity to the effects of metasomatic mixing between two end-members. The investigated primitive Etnean magmas showed a variable REE enrichment respect to MORB (Lan/Ybn =11-26) and isotopic values of Sr, Nd and He in the following ranges: 143Nd/144Nd= 0.512869 -0.512896; 86Sr/87Sr=0.70330 - 0.70370; 3He/4He = 7-7.6 Ra. A variable melting degree of a common mantle source together with a variable level of crystallization and crustal contamination is hypothesised to explain the variations exhibited by the above Etnean dataset. Numerical simulation performed on MELT code allowed to estimate the trace elements content of the Etnean mantle source. These results, joined to the most primitive isotopic values of He- Sr- Nd among the investigated products helped to geochemically characterize the mantle beneath the Etnean area suggesting a strict relation with that Hyblean. Indeed, the modeled Etnean source locates on the mixing zone between the Hyblean peridotite and pyroxenite, so testifying a simultaneous contribution of two components in the genesis of the investigated lavas and supporting the hypothesis of an heterogeneous and metasomatized lithosphere common to both areas.

Peralkaline silicic magmas were erupted at Pantelleria in a variety of eruptive typologies and magnitudes: pyroclastic flows, Plinian to strombolian pumice fallout and lava flows. The initial cycle (330- 180 ka) was characterized mainly by effusive activity, and was followed by an intermediate cycle (181 - 85 ka), characterized by a clear drift to explosive activity. This period, onto we focus, is bracketed by six ignimbrite-forming eruptions (older and intermediate of the two caldera collapses at 140 and 50 ka that characterize the volcanological history of the island, which drained silicic and variably peralkaline magma for a cumulative volume close to 6 km3 DRE. These ignimbrites lack of continuity among the few outcrops (commonly in vertical scars) and also suffer from strong welding and rheomorphism. First reconstructions and correlations [Mahood and Hildreth, 1986], although still valid for many aspects, suffer from the poor precision of K/Ar ages, especially when Ar excess and xenocrystic contamination are common, as is the case for Pantelleria lavas and pyroclastic rocks. Recently, new correlations based on paleomagnetic methods [Speranza et al., 2012] succesfully identified and correlated two welded pyroclastic breccias outcropping in the NE and SW sectors of the island with the old caldera collapse, and also demonstrated the equivalence of two other ignimbrite units previously considered as separate eruptions. Based on 14 new 40Ar/39Ar ages (laser heating on anorthoclase feldspar separates) ages and petrographic data, we propose an updated stratigraphy for the intermediate period and to provide accurate age brackets to the correlations. Recently, the application of 40Ar/39Ar methods on much younger (age < 20 ka) silicic lavas and tephra at Pantelleria [Scaillet et al., 2011], demonstrated highly precise and contributed to unravel the complex post-Green Tuff stratigraphy. Our results can be summarized as follows: - The pre-La Vecchia caldera eruptive history ended with the emplacement of two trachytic ignimbrites (at 181 ± 1.2 ka and 171 ± 1.7 ka), which were emplaced only in the south sector of the island. Both were truncated by the old (La Vecchia) caldera collapse. - The age of the old caldera collapse is now tightly constrained between 139-146 ka , i.e. the new age of the welded pyroclastic breccia (previously undated). that represents the caldera-forming eruption [Speranza et al., 2012]. - After the La Vecchia caldera collapse, the first ignimbrite eruption occurred at 123 ka with a trachy-comenditic and crystal-rich unit emplaced in the NE to NW sectors of the island. - At 107 ka a crystal-rich trachytic ignimbrite was erupted, together with some fines-rich lobes that (K/Ar ages) were previously considered as two different units, but with similar 40Ar/39Ar ages. - Higher up in the stratigraphic sequence, two previously considered different ignimbrites (for an inferred volume of erupted magma close to 1.5 km3 DRE) demonstrated coeval by 40Ar/39Ar dating, and together are part of an eruptive paroxysm at 85 ka comparable in magnitude to the Plinian eruption of the Green Tuff (age 50 ka), - The the recurrence time of the above mentioned eruptions, for a cumulative erupted magma volume close to 6 km3 DRE, suggest that at the end of the inter-eruptive period 85-50 ka the production and evolution rates of pantellerite magma peaked to reach a maximum peralkalinity.