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South-Eastern Spain is a key locality of the Western Mediterranean to unravel the origin of post-collisional magmatism and its relationships with the multi-stage evolution of the upper mantle in complex geodynamic settings. This study is focused on the Plio-Pleistocene post-collisional intraplate-like alkali basalts cropping out in the Tallante area (South-Eastern Spain) that are erupted in a region previously characterised by subduction related calc-alkaline to ultrapotassic (i.e., lamproitic) volcanism. Tallante alkali basalts represent a volcanic episode similar to other contemporary small volume intraplate volcanic occurrences of Western-Central Europe and North Africa, which are believed to derive from a Common Mantle Reservoir characterising the entire Circum Mediterranean asthenosphere. We report new major, trace element, and Sr-Nd-Pb isotope data on Tallante alkali basalts, showing compositions broadly similar to the other mafic volcanic rocks derived from the Common Mantle Reservoir and thus suggesting an asthenospheric component similar to other European within plate volcanic rocks. On the other hand, specific trace element ratios, such as Ce/Pb, Nb/U, Th/Yb, along with delta207Pb/204Pb and 87Sr/86Sr, clearly indicate the involvement of an enriched, subduction-related component, with a lamproitic geochemical and isotopic flavour. The trace element ratios suggest that low melting degree magmas from the Common Mantle Reservoir infiltrated and triggered melting of the strongly metasomatised sub-continental lithospheric mantle, which produced the lamproitic magmas previously erupted in the same area. The proposed origin of Tallante alkali basalts, located along a large scale left-lateral strike-slip fault, is consistent with analytical, numerical and laboratory models indicating that narrow subduction zones such as the Gibraltar Arc are characterised by mantle inflow around the slab edges determining upwelling and adiabatic melting of the asthenospheric mantle through slab tears.

High-MgO lamproite and lamproite-like (i.e. lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine-Himalayan collisional margin, which followed the closure of the Tethys Ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g. plugs, dykes and laccoliths) and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (northern Italy), through the Late Miocene in Corsica (southern France) and in Murcia-Almeria (southeastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (central Italy), in the Balkan peninsula (Serbia and Macedonia) and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent, and it is rarely found only in the groundmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time-integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatized by at least two different agents: (1) a high Th/La and Sm/La (i.e. SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; (2) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterized by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterize areas that were affected by multiple Wilson cycles, as observed in the Alpine-Himalayan Realm.

An analytical protocol for high-precision, in situ microscale isotopic investigations is presented here, which combines the use of a high-performing mechanical microsampling device and high-precision TIMS measurements on micro-Sr samples, allowing for excellent results both in accuracy and precision. The present paper is a detailed methodological description of the whole analytical procedure from sampling to elemental purification and Sr-isotope measurements. The method offers the potential to attain isotope data at the microscale on a wide range of solid materials with the use of minimally invasive sampling. In addition, we present three significant case studies for geological and life sciences, as examples of the various applications of microscale 87Sr/86Sr isotope ratios, concerning (i) the pre-eruptive mechanisms triggering recent eruptions at Nisyros volcano (Greece), (ii) the dynamics involved with the initial magma ascent during Eyjafjallajökull volcano’s (Iceland) 2010 eruption, which are usually related to the precursory signals of the eruption, and (iii) the environmental context of a MIS 3 cave bear, Ursus spelaeus. The studied cases show the robustness of the methods, which can be also be applied in other areas, such as cultural heritage, archaeology, petrology, and forensic sciences.

Ultramafic xenoliths are rarely found at convergent plate margins. A notable exception is in the Betic Cordillera of southern Spain, where the eruption of xenolith-bearing alkaline basalts during the Pliocene post-dated the Cenozoic phase of plate convergence and subduction-related magmatism. Mantle xenoliths of the monogenetic volcano of Tallante display extreme compositional heterogeneities, plausibly related to multiple tectono-magmatic episodes that affected the area. This study focuses on two peculiar composite mantle xenolith samples from Tallante, where mantle peridotite is crosscut by felsic veins of different size and mineralogy, including quartz, orthopyroxene, and plagioclase. The veins are separated from the peridotite matrix by an orthopyroxene-rich reaction zone, indicating that the causative agents were alkali-rich hydrous silica-oversaturated melts, which were likely related to recycling of subducted continental crust components. The present study reports new and detailed major and trace elements and Sr-Nd-Pb analyses of the minerals in the composite Tallante xenoliths that confirm the continental crust derivation of the metasomatic melts, and clarifies the mode in which subduction-related components are transferred to the mantle wedge in orogenic areas. The particular REE patterns of the studied minerals, as well as the variation of the isotopic ratios between the different zones of the composite xenoliths, reveal a complex metasomatic process. The distribution of the different elements, and their isotope ratios, in the studied xenoliths are controlled by the mineral phases stabilised by the interaction between the percolating melts and the peridotitic country rock. The persistence of marked isotopic heterogeneities and the lack of re-equilibration suggest that metasomatism of the sub-continental lithospheric mantle occurred shortly before the xenolith exhumation. In this scenario, the studied xenoliths and the metasomatic processes that affected them may be representative of the mantle sources of mafic potassic to ultrapotassic magmas occurring in post-collisional tectonic settings.

The Mediterranean area is one of the most intriguing places on Earth where geodynamics and volcanoes are strictly related, and evolved through time. The complexity of the tectonic setting is further enriched by the observed shift of the petrochemical affinity of magmas, in the same volcanic area, from subduction-related to intraplate. The successive opening of back-arc basins (e.g., Ligurian-Provençal basin, Tyrrhenian Sea), following the roll-back of the subducting Adria Plate, produced a migration of magmatism to form a transitional eastward pattern of volcanoes both onshore and offshore. The Mio-Pliocene volcanic rocks occurring in the Central Mediterranean area are characterised by exceptional variability of the petro-chemical and isotopic features, which allow the distinction of several sectors, when also the areal distribution is considered. Thus, the Mediterranean area has always been site of studies focused on magma genesis and on the geodynamic significance of the complex scenario achieved through time. In the scientific literature, a large number of papers were published on the magmatism of each single volcanic association/area, but very few dealt with the general picture of the offshore magmatic and geodynamic evolution. The aim of this chapter is to provide an outline of the most prominent geological, petrological, geochemical and isotopic characteristics of the submarine volcanic centres found in the Central Mediterranean basin, with the aim of providing a fairly complete picture of the existing relationships between the geodynamics and the igneous petrology in this area.

The active volcano of Ischia, the well-known island off-shore the city of Naples, has had a discontinuous volcanic activity characterised by caldera-forming paroxysmal eruptions, lava flows, and lava domes for >150 kyr. The overall geochemical composition of erupted magmas includes shoshonite, latite, and trachyte/trachyphonolite. In a complementary study, we demonstrated that the evolution of Ischia trachytes with Sr 10 wt.% outcrop a few kilometers apart at Procida island, and suggest that the evolved latites and trachytes at Ischia might have originated by crustal assimilation processes affecting Procida basalts. However, Energy Constrained Assimilation and Fractional Crystallisation modelling sets robust constraints against this hypothesis and provide geochemical arguments for a pristine mantle-derived radiogenic isotope signature for trachytes and latites, implying that they also evolved from parental basaltic magmas in a closed-system environment akin to trachytes with Sr

The fate of carbonate-rich sediments recycled at destructive plate margins is a key issue for constraining the budget of deep CO2 supplied to the atmosphere by volcanism. Experimental studies have demonstrated that metasomatic melts can be generated by partial melting of subducted carbonate-pelitic sediments, but signatures of the involvement of such components in erupted magmas are more elusive. We have made new U-Th disequilibria, Sr-Nd-Pb isotope, and high-precision delta238U analyses on lavas from Mount Vesuvius (Italy) and show that their measured 238U excesses require a mantle source affected by the addition of U-rich carbonated melts, generated by partial melting of subducted calcareous sediments in the presence of residual epidote. Accordingly, we argue that the occurrence of 238U excesses in "sediment-dominated" arc magmas represents diagnostic evidence of addition of carbonate sediments via subduction, hence providing constraints on deep carbon cycling within Earth. Our quantitative enrichment model, combined with published experimental results, allows us to estimate a resulting flux of 0.15-0.8 Mt/yr CO2 from the subducted carbonates to the mantle source of Mount Vesuvius.