Description: The Cenozoic igneous activity of Sardinia is essentially concentrated in the 38-0.1 Myr time range. On the basis of volcanological, petrographic, mineralogical, geochemical and isotopic considerations, two main rock types can be defined. The first group, here defined SR (Subduction-Related) comprises Late Eocene-Middle Miocene (~ 38-15 Ma) igneous rocks, essentially developed along the Sardinian Trough, a N-S oriented graben developed during the Late Oligocene-Middle Miocene. The climax of magmatism is recorded during the Early Miocene (~ 23-18 Ma) with minor activity before and after this time range. Major and trace element indicators, as well as Sr-Nd-Pb-Hf-Os-O isotope systematic indicate complex petrogenetic processes including subduction-related metasomatism, variable degrees of crustal contamination at shallow depths, fractional crystallization and basic rock partial melting. Hybridization processes between mantle and crustal melts and between pure mantle and crustally contaminated mantle melts increased the isotopic and elemental variability of the composition of the evolved (intermediate to acid) melts. The earliest igneous activity, pre-dating the Early Miocene magmatic climax, is related to the pushing effects exerted by the Alpine Tethys over the Hercynian or older lower crust, rather than to dehydration processes of the oceanic plate itself. The second group comprises volcanic rocks emplaced from ~ 12 to ~ 0.1 Ma. The major and, partially, trace element content of these rocks roughly resemble magmas emplaced in within-plate tectonic settings. From a Sr-Nd-Pb-Hf-Os isotopic point of view, it is possible to subdivide these rocks in two subgroups. The first, defined RPV (Radiogenic Pb Volcanic) group comprises the oldest and very rare products (~ 12-4.4 Ma) occurring only in the southern sectors of Sardinia. The second group, defined UPV (Unradiogenic Pb Volcanic), comprises rocks emplaced in the remaining central and northern sectors during the ~ 4.8-0.1 Ma time range. The origin of the RPV rocks remains quite enigmatic, since they formed just a few Myr after the end of a subduction-related igneous activity but do not show any evidence of slab-derived metasomatic effects. In contrast, the complex origin of the mafic UPV rocks, characterized by low 206Pb/204Pb (17.4-18.1), low 143Nd/144Nd (0.51232-0.51264), low 176Hf/177Hf (0.28258-0.28280), mildly radiogenic 87Sr/86Sr (~ 0.7044) and radiogenic 187Os/188Os ratios (0.125-0.160) can be explained with a mantle source modified after interaction with ancient delaminated lower crustal lithologies. The strong isotopic difference between the RPV and UPV magmas and the absence of lower crustal-related features in the SR and RPV remain aspects to be solved.

Description: The central-western Mediterranean area is a key region for understanding the complex interaction between igneous activity and tectonics. In this review, the specific geochemical character of several ‘subductionrelated’ Cenozoic igneous provinces are described with a view to identifying the processes responsible for the modifications of their sources. Different petrogenetic models are reviewed in the light of competing geological and geodynamic scenarios proposed in the literature. Plutonic rocks occur almost exclusively in the Eocene–Oligocene Periadriatic Province of the Alps while relatively minor plutonic bodies (mostly Miocene in age) crop out in N Morocco, S Spain and N Algeria. Igneous activity is otherwise confined to lava flows and dykes accompanied by relatively greater volumes of pyroclastic (often ignimbritic) products. Overall, the igneous activity spanned a wide temporal range, from middle Eocene (such as the Periadriatic Province) to the present (as in the Neapolitan of southern Italy). The magmatic products are mostly SiO2-oversaturated, showing calcalkaline to high-K calcalcaline affinity, except in some areas (as in peninsular Italy) where potassic to ultrapotassic compositions prevail. The ultrapotassic magmas (which include leucitites to leucite-phonolites) are dominantly SiO2-undersaturated, although rare, SiO2-saturated (i.e., leucite-free lamproites) appear over much of this region, examples being in the Betics (southeast Spain), the northwest Alps, northeast Corsica (France), Tuscany (northwest Italy), southeast Tyrrhenian Sea (Cornacya Seamount) and possibly in the Tell region (northeast Algeria). Excepted for the Alpine case, subduction-related igneous activity is strictly linked to the formation of the Mediterranean Sea. This Sea, at least in its central and western sectors, is made up of several young (b30 Ma) V-shaped back-arc basins plus several dispersed continental fragments, originally in crustal continuity with the European plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle ‘wedge’ regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO2 and H2O in the fluid phase released by the subducting plates are the most important. Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) entrifugal wave of both compressive and extensional tectonics starting from a ‘pivotal’ region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction ‘inversion’ events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subductionrelated magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related ‘exotic’ (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the hanging-wall of the Late Cretaceous–Eocene Adria–Europe subduction system in the Alps); i) voluminous production of subductionrelated magmas coeval with extensional tectonic régimes (e.g., during Oligo-Miocene Sardinian Trough formation). To summarize, these salient central-western Mediterranean features, characterizing a late-stage of the classic ‘Wilson Cycle’ offer a ‘template’ for interpreting magmatic compositions in analogous settings elsewhere.

Description: A diffuse and voluminous (〉1400 km3) Miocene-Quaternary volcanic activity developed around the Karlıova Triple Junction in East Anatolia as a consequence of collisional tectonics among Anatolia, Arabia and Eurasia continental plates. The volcanic rocks of this region are grouped into three phases of activity: 1) Early Phase (Solhan volcanism; ~7.3–4.4 Ma), with emplacement of alkali basalt to trachyte lava flows and pyroclastic successions; 2) Middle Phase (Turnadağ and Varto volcanism; ~3.6–2.6 Ma), mostly with products with the same compositional range plus minor dacites and rhyolites, and 3) Late Phase (Özenç volcanism; ~2.6–0.5 Ma), with emplacement of alkali basaltic, hawaiitic and mugearitic lavas and dykes. Primitive Mantle-normalized patterns of the three rock groups share an enriched LILE and depleted HFSE contents, with overall positive spikes of Pb and mildly fractionated LREE/HREE trends showing more similar affinity to global subducting sediments rather than to magmas emplaced in mid-plate settings (i.e., OIB). Initial Sr isotopic ratios of the least evolved compositions range from values lower than BSE (87Sr/86Sri = 0.7041) to radiogenic compositions (87Sr/86Sri = 0.7050). They reflect either FC-like processes, with 87Sr/86Sri up to 0.7064, or closed system fractional crystallization, with 87Sr/86Sri = 0.7046–0.7049. Initial Nd are higher than ChUR estimate for the most and the least evolved compositions (143Nd/144Ndi = 0.51267–0.51280), indicating provenance from isotopically depleted sources. Lead isotopic ratios are characterized by a remarkable homogeneous 206Pb/204Pb (18.95–19.04), with 207Pb/204Pb (15.65–15.72) and 208Pb/204Pb (38.87–39.21) slightly above the Northern Hemisphere Reference Line, pointing towards the EMII end-member. Geochemical modelling for the least evolved volcanic units indicate the likely generation from an amphibole-bearing spinel-lherzolitic source. P-T calculations for partial melting calculations gave lithospheric pressures for initial magma generation (0.8–1.3 GPa). Possible cause of melting might be related to passive upwelling of asthenosphere as a response to the local extension linked to the development of North Anatolian and East Anatolian Fault Zones. Anyhow, volcanic units from the KTJ display only limited geochemical signatures of garnet-bearing sources, or any HIMU-OIB like characteristics, as instead observed in the other portions of the Eastern Anatolia. The long-lasting complex tectonic evolution of the Eastern Anatolia is responsible for the large geochemical variability of the magmatic products. However, the general characteristics of KTJ volcanic rocks are mainly dominated by subduction-related signatures, with most of the primary magma characteristics having been heavily masked by fractionation and crustal assimilation processes.

Description: The composition of the upper mantle bounded by the Canaries, Eastern Anatolia, Libya and Poland is indirectly investigated by means of the chemical composition of igneous rocks with anorogenic' geochemical characteristics emplaced during the Cenozoic. The relatively homogeneous composition of these products in terms of incompatible trace-element content and Sr-Nd-Pb isotopic composition is unexpected, considering the variable lithospheric structure of this large area and the different tectono-thermal histories of the various districts. In order to reconcile the geochemical characteristics with a statistical sampling model, it would be necessary to propose volumes of the enriched regions much lower than the sampling volumes for each volcano (that is, less than 10 cubic metres), or alternatively, efficient magma blending from larger areas. The data are consistent with a relatively well-stirred and mixed sub-lithospheric upper mantle, in the solid state, which is also hard to understand. This contrasts with the situation under oceans where magma blending from diverse sources and sampling theory can explain the compositional statistics.

Description: During Ocean Drilling Program Leg 200, ~45 Ma igneous basement, was cored in the northeastern Pacific at Site 1224. The basement surface was inferred to be 28 meters below seafloor (mbsf). Basement lithology down to 170 mbsf is divided into three major units: Unit 1 = massive flow, Unit 2 = pillow breccia, and Unit 3 = intermixed pillows and thin flows. The bulk compositions of Site 1224 rocks have high abundances of the high-field strength elements (HFSE) Y, Zr, and Nb relative to normal and even enriched mid-ocean-ridge basalts. Chemical stratigraphic differences among the three units at this site are clear. Unit 3 rocks have the highest FeO/MgO ratio and HFSE concentration, and Unit 2 lavas have the lowest. Unit 2 lavas also have the highest Y/Zr ratios. Unit 1 is separated into lower and upper flow units based on differences in HFSE content. Clearly, there were significant differences in the petrogenetic processes that created these units. Compositional and lithologic differences among the basement units correlate with differences in physical properties among the units described by the Leg 200 Shipboard Scientific Party. Physical properties are therefore associated with petrological features.