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The process of peridotite hydration, or serpentinization, is known to generate reducing conditions through the production of H2-CH4-rich fluids. The release of these abiotic energy sources has attracted a broad scientific attention spanning natural energy research, carbon cycling, and deep subsurface microbiology and astrobiology. Serpentinization is documented at various geological settings including sub-seafloor hydrothermal systems and at much higher pressures and temperatures in subduction zones. Determining the conditions at which serpentinization and H2 release occur is crucial to comprehensively understand the geochemical cycle of life-essential, redox-sensitive elements such as C in subduction zones and the potential supply of energy to the deep subsurface biosphere. However, especially at convergent margins, ultramafic rocks may record multiple serpentinization events ranging from seafloor to subduction metamorphic conditions, which challenges the study of this key geological process. Petrographic and geochemical tracers, such as δ11B, have been used to disentangle multiple serpentinization events taking place at different geodynamic settings and/or from different fluid sources. However, petrographic features may be of ambiguous interpretation, and boron isotope data may show significant overlap among different serpentinization conditions.To tackle these open questions, we adopted a high-resolution approach at the massif scale within the blueschist-facies Monte Maggiore ultramafic body, Alpine Corsica, France. This massif recorded the critical conditions of the lizardite/antigorite transition, which makes it an ideal case to study preserved and structurally controlled serpentinization events. We collected more than 150 samples of partially to fully serpentinized peridotites over an area of about 1Km2. The samples were selected and processed for petrographic analysis, Raman Spectroscopy, major and trace elements and δ11B with the aim of reconstructing a massif-scale distribution of multiple serpentinization events. Four main serpentine generations were identified: lizardite/chrysotile, lizardite/antigorite, sole antigorite, and late chrysotile. These generations show characteristic and systematic features, and their association defines a limited number of sample types at the massif scale. Bulk δ11B analyses show a wide range of values, from -2.51 to 23.33 ‰, which overlap with both slab and ocean derived fluids. When compared with petrographic data, it appears that samples belonging to the same sample type, therefore sharing common mineralogical and microstructural features characteristic of a specific serpentinization process, show substantially different boron isotopic values.Our results indicate that large petrographic and δ11B variability may exist within a single serpentinized ultramafic massif, and also among samples plausibly belonging to the same serpentinization event. This high-resolution study of serpentinization events at the massif scale calls for caution while interpreting large-scale serpentinization processes through the study of individual samples or small sample sets inferred to represent large geodynamic contexts.

The Cenozoic Arabia–Iran continental collision was associated with emplacement of a large variety of magmatic rock types. This aspect is particularly evident in the Bijar-Qorveh area of NW Iran, where Miocene andesitic to rhyolitic rocks and Quaternary basic alkaline rocks crop out. The Miocene intermediate to acid products show radiogenic Sr and Pb isotopic compositions (87Sr/86Sri 0.70531–0.71109, 206Pb/204Pb 18.71–19.01, 207Pb/204Pb 15.66–15.73, 208Pb/204Pb 38.76–39.14), coupled with unradiogenic Nd isotopic ratios (143Nd/144Ndi 0.51223–0.51265). These characteristics, together with primitive mantle-normalised multielemental patterns resembling ‘subduction-related’ geochemical fingerprints, are considered ultimately derived from the Iranian plate mantle wedge, metasomatised during previous NE-directed Neothetyan Ocean subduction. The alkali-rich andesitic and dacitic rocks evidence both closed- and open-system differentiation, as typically observed for collisional settings in general. Both rock types display a high Sr/Y (37–100) and La/Yb (29–74) ‘adakitic’ signature that it is interpreted here with plagioclase (± amphibole) accumulation or melting of local mafic crustal rocks. Open-system processes involve recycling of crustal cumulates for pyroxene-rich andesite and biotite-rich dacite varieties and low-degree partial melting of the local crust for rhyolites. A radical change occurred during the Quaternary, when SiO2-understaturated to SiO2-saturated poorly evolved rocks (basanites, tephrites, alkaline and subalkaline basalts) were emplaced. The complete change of mantle sources suggests a phase of local extensional tectonics related with WNW-ESE right-transcurrent faults. The major oxide, as well as incompatible trace element and Sr-Nd-Pb isotopic fingerprint of these younger rocks is more akin to that of intraplate magmas, but still bearing some evidences for a variable contribution from a ‘subduction-modified’ mantle source. The NW-trend of increasing involvement of this subduction component is indicative of the strong tectonic control on magmatism. Additional lithotypes indicate the presence of open-system differentiation and remelting processes in the youngest phase of magmatic activity.

The Pleistocene Intra-Apennine Province (IAP) in central Italy contains several small volume eruptive centres, characterized by basic-ultrabasic lithologies, often characterized also by ultracalcic and ultrapotassic compositions. They are emplaced above the thick carbonate and evaporite sedimentary sequence of the Apennine Chain. The small monogenetic volcano of Cupaello (~640 ka) offers the chance to investigate exotic volcanic rocks such as ultracalcic kamafugites, known in literature as coppaelite. This volcano also offers the opportunity to study the interaction of ultrabasic melts with sedimentary carbonates (Maiolica Formation). Indeed, assimilation of local carbonate-rich sediments has been already documented as a likely process at least in the neighbouring IAP volcanoes of San Venanzo [1] and Polino [2] volcanoes. On the other hand, alternative views considers the CaO-rich (CaO up to 38.8 wt%) and SiO2-poor (SiO2 down to 14.2 wt%) composition of some Cupaello pyroclastic rocks a reflection of a carbonatitic component in their mantle source [3]. Cupaello lavas are ultrabasic (silica = 42.6-44.1 wt%) and ultrapotassic (K2O = 5.2-7.6 wt%; K2O/Na2O = 18.0-33.9) rocks, characterized by euhedral to subhedral phenocrysts of clinopyroxene and phlogopite set in a hypohyaline-hypocrystalline groundmass made of melilite, kalsilite, phlogopite, olivine, calcite and glass. Perovskite, opaques, wollastonite, monticellite and apatite represent the accessory phases. The trace element signatures of Cupaello kamafugites, such as high LILE (e.g., Rb = 482-673 ppm), high LILE/HFSE ratios (Ba/Nb = 71-82), negative Eu anomalies (Eu/Eu* = 0.68-0.72), as well as the presence of negative anomalies for Nb, Ta, P and Ti coupled with peaks for Pb in primitive mantle-normalized diagrams are compatible with the derivation from a subduction-modified source [4]. Isotopic ratios confirm this hypothesis, with the presence of strongly radiogenic 87Sr/86Sr (0.71123-0.71125), unradiogenic 143Nd/144Nd (0.51200-0.51207) and 206Pb/204Pb isotopic ratios buffered to 18.76. The negative correlation of major oxides and trace elements with CaO, pointing toward an end-member represented by the Apennines limestone lithologies, offers an alternative hypothesis to the widely accepted presence of a carbonatitic component. The very small volume of emplaced magma, as well as the thick carbonate succession to be pierced to reach the surface renders unavoidable strong crustal assimilation by the original magma. The high Fo (89.5-90.2) in Cupaello olivine, as well as the thin border of monticellite around the rare olivine could be explained by assimilation of limestone wall rock, as demonstrated experimentally [5]. The CaO-richest (CaO up to 38.8 wt%) and SiO2-poorest (SiO2 down to 14.2 wt%) compositions are found in pyroclastic/epiclastic deposits (no longer available for sampling). We believe that these whole-rock compositions reflect the presence of abundant, almost completely sterile, secondary calcite. Bibliography [1] Lustrino et al., 2020, Earth-Sci. Rev., 208, 103256. [2] Lustrino et al., 2019, Sci. Rep., 9, 1-14. [3] Stoppa and Cundari, 1995, Contrib. Mineral. Petrol., 122, 275-288. [4] Carminati et al., 2012, Tectonophysics., 579, 173-192. [5] Lustrino et al., 2022, Geology, https://doi.org/10.1130/G49621.1

The northernmost sector of the western branch of the East African Rift (EAR) includes the young (~40-50 ka [1]) volcanic province of Toro Ankole, characterized by the presence of exotic volcanic products such as carbonatites, melilitites, kamafugites and foidites [2]. Among these, the occurrence of kamafugites (kalsilite-bearing volcanic rocks [3]) is noteworthy, as Toro Ankole represents the type locality for these compositions, found in only two other localities worldwide. The Toro Ankole volcanic province developed along the margin of the Archean Tanzanian craton, and its magmatic products show the influence of metasomatic processes and phases developed in the thick continental lithosphere. Indeed, MARID-like metasomatism is proposed in literature, with the formation of a veined mantle [4]. A multidisciplinary approach, based on a detailed petrographic, mineral chemical, geochemical and isotopic (Sr, Nd, Pb and B) study, has been carried out on 53 samples, which include not only lavas and tuffs, but also holocrystalline and wall rock xenoliths. Two types of lava may be identified: the first is represented by carbonatites and silico-carbonatites, characterized by low SiO2 (4.89-21.78 wt%) and low alkali (0.44-2.03 wt%) and high CaO (25.17-47.57 wt%), while the second most peculiar lithotypes is represented by kamafugites; katungites (melilite-rich kalsilite-olivine-bearing volcanic rocks), mafurites (kalsilite-rich melilite-olivine-bearing) and ugandites (olivine-rich kalsilite-melilite-bearing). The kamafugites are strongly SiO2-undersaturated and moderately ultrabasic, potassic to ultrapotassic volcanic rocks, with high MgO (6.08-22.20 wt%) and CaO (up to 15.46 wt%). They consist of phenocrysts of clinopyroxene and olivine set in a hypo-holocrystalline fine-grained groundmass made up of microliths of clinopyroxene, olivine, perovskite, kalsilite, nepheline, leucite, melilite, phlogopite, carbonates and opaques. The xenolith cargo shows wide range of compositions, varying from clinopyroxenite to glimmerite, with low modal abundance of opaques and perovskite in agreement with the literature data that generally report a lack of olivine and orthopyroxene in the mineral assemblage [5]. The common presence of phlogopite, abundant clinopyroxene and carbonate-rich veins indicate the presence of veined lithosphere [6]. This is consistent with the isotopic data for lavas and xenoliths (87Sr/86Sr = 0.70480-0.70563 and 143Nd/144Nd = 0.512515-0.512575), which outlines an enriched and complex mantle source. 206Pb/204Pb is extremely variable, with values from the holocrystalline xenolith (19.99-19.27) being slightly higher than lava samples (19.28-19.63). The d11B values for lavas and xenoliths, show a wide range, varying from DMM-like values (-6 and -8‰) to more variable OIB-like values (down to -12 and up to -3‰; [7]), through to positive values (up to +6.6‰ in the lavas). These latter also exhibit the highest Sr isotopic ratios of the dataset, pointing to the possible occurrence of old and altered oceanic crust and/or serpentinite in the mantle source. Bibliography [1] Boven et al., 1998, J. Afr. Earth Sci., 26, 463-476.[2] Holmes and Harwood, 1932, Quarterly J. Geol. Soc., 88, 370-442.[3] Le Maitre, 2002, Cambridge University Press.[4] Rosenthal et al., 2009, Earth Planet. Sci. Lett., 284, 236-248.[5] Link et al., 2008, 9th Int. Kimb. Conf., 1-3.[6] Foley, 1992, Lithos, 28, 435-453.[7] Agostini et al., 2021, Sci. Rep., https://doi.org/10.1038/s41598-021-90275-7.

Melt storage and supply beneath arc volcanoes may be distributed between a central stratovolcano and wider fields of monogenetic cones, indicating complex shallow plumbing systems. However, the impact of such spatially variable magma storage conditions on volatile degassing and trace element geochemistry is unclear. This study explores magma generation and storage processes beneath the Tolbachik volcanic field, Kamchatka, Russia, in order to investigate the evolution of the magmatic volatile phase and, specifically, the strong enrichment of chalcophile metals (in particular, Cu) in this system. We present new geochemical data for a large suite of olivine- and clinopyroxene-hosted melt inclusions (and host phenocrysts) from five separate monogenetic cones within the Tolbachik volcanic field. These high-Al composition magmas likely reflect the homogenised fractionation products of primitive intermediate-Mg melt compositions, stored at shallow depths after significant fractional crystallisation. Boron isotope compositions and incompatible trace element ratios of the melt inclusions suggest a deeper plumbing system that is dominated by extensive fractional crystallisation and fed by melts derived from an isotopically homogeneous parental magma composition. Volatile components (H2O, CO2, S, Cl, F) show that magmas feeding different monogenetic cones had variable initial volatile contents and subsequently experienced different fluid-saturated storage conditions and degassing histories. We also show that melts supplying the Tolbachik volcanic field are strongly enriched in Cu compared with almost all other Kamchatka rocks, including samples from the Tolbachik central stratocones, and other volcanoes situated in close proximity in the Central Kamchatka Depression. The melt inclusions record Cu concentrations ≥450 μg/g at ca. 4–5 wt.% MgO, which can only be explained by bulk incompatible partitioning behaviour of Cu, i.e. evolution under sulphide-undersaturated conditions. We suggest that initial mantle melting in this region exhausted mantle sulphides, leading to sulphide undersaturated primitive melts. This sulphide-free model for the high-Al cone melts is further supported by S/Se and Cu/Ag values that overlap those of the primitive mantle and MORB array, with bulk rock Cu/Ag ratios also overlapping other with other global arc datasets for magma evolution prior to fractionation of a monosulfide solid solution. We therefore demonstrate that the combination of novel chalcophile metal analyses with trace element, isotopic, and volatile data is a powerful tool for deciphering complex magmatic evolution conditions across the entire volcanic field.

Evidence of hydrothermal activity is reported for the Mesozoic pre- and syn-rift successions of the western Adriatic palaeomargin of the Alpine Tethys, preserved in the Western Southalpine Domain (NW Italy). The products of hydrothermal processes are represented by vein and breccia cements, as well as dolomitization and silicification of the host rocks. In the eastern part of the study area, interpreted as part of the necking zone of the continental margin, Middle Triassic dolostones and Lower Jurassic sediments are crossed by veins and hydrofracturing breccias cemented by saddle dolomite. The precipitation of dolomite cements occurred within the stratigraphic succession close to the sediment-water interface. Despite the shallow burial depth, fluid inclusion microthermometry and clumped isotopes show that hydrothermal fluids were relatively hot (80-150 degrees C). In the western part of the study area, interpreted as part of the hyperextended distal zone, a polyphase history of host-rock fracturing is recorded, with at least two generations of veins cemented by calcite, dolomite and quartz. Vein opening and cementation occurred at shallow burial depth around the time of deposition of the syn-rift clastic succession. Fluid inclusion microthermometry on both quartz and dolomite cements indicates a fluid temperature of 90-130 degrees C, again pointing to hydrothermal fluids. Both in Fenera-Sostegno and Montalto Dora areas, O, C and Sr isotope values, coupled with fluid inclusion and clumped isotope data, indicate that hydrothermal fluids derived from seawater interacted with crustal rocks during hydrothermal circulation. Stratigraphic and petrographic evidence, and U-Pb dating of dolomitized clasts within syn-rift sediments, document that hydrothermal fluids circulated through sediments from the latest Triassic to the Toarcian, corresponding to the entire syn-rift evolution of the western portion of the Adriatic palaeomargin. The documented hydrothermal processes are temporally correlated with regional-scale thermal events that took place in the same time interval at deeper crustal levels., Basin Research, 33 (6), ISSN:0950-091X, ISSN:1365-2117

In order to trace the cycling of fluid-mobile elements (FMEs) through subduction zone forearcs, we collected water samples from two warm and 16 cold springs along the subaerially exposed forearc of the Hikurangi subduction zone in New Zealand. Water samples were analyzed for their cation and anion concentrations, as well as their B, Li, Cl, and O stable isotope compositions. Fluids discharging through the prism have high concentrations of Cl (2400–16,000 mg/L), Br (6–70 mg/L), I (0.4–72 mg/L), Sr (0.1–200 mg/L), B (3–130 mg/L), Li (0.1–13 mg/L), and Na (33–6600 mg/L), consistent with data from previous studies. Most of these elements decrease overall in concentration from north to south, have a concentration peak in the central part of the margin, and have had limited concentration variability during the last three decades. Because Li, Cl, and B are all fluid-mobile elements, their incompatibility potentially limits modification by fluid-rock interaction, making them reliable tracers of fluid source. δ37Cl, δ11B, and δ7Li values range from −1.3‰ to +0.4‰ (n = 36), +11.8‰ to +41.9‰ (n = 25), and −3.1‰ to +29.0‰ (n = 29), respectively. Despite the change in concentrations along the margin, there is no corresponding trend in isotopic composition. Chlorine and boron isotope compositions are consistent with fluids dominated by seawater (δ37Cl = 0‰; δ11B = 40‰) and sedimentary pore fluids (δ37Cl ≈ −8‰ to 0‰; δ11B > ∼17‰). Br/Cl (0.0025–0.005) and I/Cl (0.00005–0.007) weight ratios also support a dominant seawater and pore-fluid source. Lithium isotope data also suggest fluids sourced from seawater (δ7Li = +31‰) as well as dehydrating sediments and/or modified by interaction with local sediment. The fluid geochemical data cannot be explained by a change in the fluid source along the margin, but rather by a change in the upper-plate structural permeability. In the north, extension likely results in a highly permeable forearc, whereas transpression in the south traps fluids within the upper plate and dilutes saline fluids with groundwater. Such changes in upper-plate structural permeability may influence fluid pressure conditions within the forearc, which in turn may influence the observed change in slip behavior on the interface from north Hikurangi (aseismic creep) to south Hikurangi (deep locking). This work highlights the role the upper plate may play in the geochemical modification and transport of slab-derived fluids, and supports the long-standing but poorly documented assumption that seawater and pore fluids are expelled at shallow levels in the subduction zone (

Hydrogeochemical changes before Mw ≥ ∼5.0 earthquakes are hoped to be applicable as seismic precursors. It is now necessary to pass from single experiences to structured networks, systematically monitoring large seismic areas for long periods. Our aim is to provide a pilot methodological experience for how such networks could be realized and the types of results they could deliver. We present the method and some initial results to document the method’s applicability. In 2017, we started the HydroQuakes project in seismically active central Italy, with the Sulmona and Matese areas selected as the two monitoring nodes. Each node includes 5–6 monitored springs, and for each spring, we performed laboratory analyses of major and trace elements and some isotopes. We installed in situ probes for continuous monitoring. Between December 2017 and January 2020, the most energetic earthquakes were three events with Mw of 3.9, 4.1, and 4.4. They were not preceded by significant hydrogeochemical anomalies, except for the Mw 4.1 event. Despite its low Mw, this earthquake occurred over a large normal fault at a great depth in the crust (∼17 km) and was preceded by weak but detectable hydrogeochemical anomalies of boron and δ11B that were similar but milder than the hydrogeochemical anomalies before the 2016 Mw 6.0 earthquake in the central Apennines. This and previous evidence show the B and δ11B hydro-seismo-sensitivity and indicates that pre-seismic hydrogeochemical anomalies could arise mostly before Mw ≥ ∼5.0 earthquakes, with weak exceptions occurring in specific conditions such as long and deep faults.

Late Miocene to Pleistocene volcanism within the Vardar zone (North Macedonia) covers a large area, has a wide range in composition and it is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. The scattered potassic to ultrapotassic volcanism developed south from the Scutari-Peć fault zone since 6.57 Ma [1]. The focus of this study is on three volcanic centers located on deep structures or thrust faults along the western part of the Vardar zone, for which there is none to very little geochronological and geochemical data available. Pakoševo and Debrište localities are represented as small remnants of lava flows cropping out at the southern edge of Skopje basin and at the western edge of Tikveš basin, respectively. Šumovit Greben center is considered as part of the Kožuf-Kozjak/Voras massif (6.5-1.8 Ma [1]), and it is located on its westernmost side, at the southern edge of Mariovo basin, which is largely comprised of volcanoclastic sediments. Here we present new eruption ages applying the unspiked Cassignol-Gillot K-Ar technique on groundmass, petrological and geochemical data, supplemented with Sr and Nd isotopes to complement and better understand the Neogene-Quaternary volcanism in the region. Obtaining the eruption ages of these volcanic centers could also help to better constrain the evolution of the sedimentary basins. All of the three centers belong to the shoshonitic series based on their elevated K-content. The oldest center amongst these three localities, as well as other Late Miocene centers within the region, is the trachyandesitic Debrište, which formed at ca. 8.1 Ma, and exhibits the highest Nd isotopic ratios (0.512441-0.512535). The trachybasaltic Pakoševo center formed at ca. 3.8 Ma and, based on its Nd isotopic ratio (0.512260), represents the strongest sign of crustal contamination. The rhyolitic Šumovit Greben center is a composite volcanic structure formed at ca. 3.0-2.7 Ma. Its youngest eruption unit has a slightly larger Nd isotopic ratio (0.512382), representing a less evolved magma at the end of its activity.This research was funded by the GINOP-2.3.2-15-2016-00009 ‘ICER’ project, the French-Hungarian Cooperation Program TÉT-FR-2018-00018 and the HORIZON 2020 grant N 676564.References:[1] Yanev et al., 2008 – Mineralogy and Petrology, 94(1-2), 45-60.

The chemical and physical processes operating during subduction-zonemetamorphismcan profoundly influence the cycling of elements on Earth. Deep-Earth carbon (C) cycling and mobility in subduction zones has been of particular recent interest to the scientific community. Here, we present textural and geochemical data (CO, Sr isotopes and bulk and in-situ trace element concentrations) for a suite of ophicarbonate rocks (carbonate-bearing serpentinites) metamorphosed over a range of peak pressure-temperature (P-T) conditions together representing a progradesubduction zoneP-Tpath. These rocks, in order of increasing peakP-Tconditions, are the Internal Liguride ophicarbonates (from the Bracco unit, N. Apennines), pumpellyite- and blueschist-facies ophicarbonates from the Sestri-Voltaggio zone (W. Ligurian Alps) and the Queyras (W. Alps), respectively, and eclogite-facies ophicarbonates from the Voltri Massif. The Bracco oceanic ophicarbonates retain breccia-like textures associated with their seafloor hydrothermal and sedimentary origins. Their trace element concentrations and δ18OVSMOW(+15.6 to +18.2‰), δ13CVPDB(+1.1 to +2.5‰) and their87Sr/86Sr (0.7058 to 0.7068), appear to reflect equilibration during Jurassic seawater-rock interactions. Intense shear deformation characterizes the more deeply subducted ophicarbonates, in which prominentcalciterecrystallization and carbonation ofserpentiniteclasts occurred. Theisotopic compositionsof the pumpellyite-facies ophicarbonates overlap those of their oceanic equivalents whereas the most deformed blueschist-facies sample shows enrichments in radiogenic Sr (87Sr/86Sr = 0.7075) and depletion in13C (with δ13C as low as −2.0‰). These differing textural and geochemical features for the two suites reflect interaction with fluids in closed and open systems, respectively. The higher-P-metamorphosed ophicarbonates show strong shear textures, with coexistingantigoriteand dolomite, carbonate veins crosscutting progradeantigoritefoliation and, in some cases, relics of magnesite-nodules enclosed in the foliation. These rocks are characterized by lower δ18O (+10.3 to 13.0‰), enrichment in radiogenic Sr (87Sr/86Sr up to 0.7096) and enrichment in incompatible and fluid-mobile element (FME; e.g., As, Sb, Pb). These data seemingly reflect interaction with externally-derived metamorphic fluids and the infiltrating fluids likely were derived from dehydrating serpentinites with hybrid serpentinite-sediment compositions. The interaction between these two lithologies could have occurred prior to or after dehydration of the serpentinites elsewhere. We suggest thatdecarbonationand dissolution/precipitation processes operating in ancient subduction zones, and resulting in the mobilization of C, are best traced by a combination of detailed field and petrographic observations, C, O and Sr isotope systematics (i.e., 3D isotopes), and FME inventories. Demonstration of such processes is key to advancing our understanding of the influence ofsubduction zonemetamorphismon the mobilization of C in subducting reservoirs and the efficiency of delivery of this C to depths beneathvolcanic arcsand into the deeper mantle.

The Pleistocene (~460–265 ka) San Venanzo volcanic complex belongs to the IAP (Intra-Apennine Province) in central Italy, which comprises at least four small Pleistocene monogenetic volcanoes plus several unrootedpyroclastic depositswith peculiar mineralogical and whole-rock chemical compositions. San Venanzo products are strongly SiO2-undersaturated, CaO- and MgO-rich and show ultrapotassic serial character. The relatively common occurrence ofcalcitein the pyroclastic rocks and the overall high CaO content are interpreted in literature as primary mineral. The main rockfaciesat San Venanzo are calcite-rich scoria and lapilli tuffs, with minor massivelava flows, and a rare pegmatoid variant (melilitolitic pockets). All the San Venanzo rocks are feldspar-free, with a typicalparagenesisof forsteritic olivine, non-stoichiometric Ca-richdiopside,melilite, leucite,kalsilite, opaque minerals,nepheline,phlogopite,calcite,apatite, cuspidine,wollastonite, kirschsteinite-monticellite s.s. ± glass and other minor and very rare minerals typical of agpaitic melts. Based on petrographic analyses, the studied rocks can be classified as olivine melilitites, olivine leucite melilitites, venanzites (a local variant of kamafugites), calcite leucite melilitolites and Ca-rich olivine leucitemelilititetuffs. Mass balance calculations indicate a direct genetic link between the lava bodies and the pegmatoid melilitolitic pocket through afractional crystallizationprocess characterized by the removal of ~74% of a melilite-bearing uganditic cumulate made up ofmelilite, leucite, olivine,kalsiliteandchromite. Primitive mantle-normalized patterns of the lavas and tuffs are rather spiked and share negative anomalies for Ba, Nb, Ta, P and Ti resembling typicalmagmasgenerated by supra-subduction mantle wedge. These compositions are very different from the only two other kamafugite localities outside Italy (Toro Ankole and Virunga in the East Africa Rift and Alto ParanaibaIgneous Provincein SE Brazil). The melilitolite sample is more incompatible element-enriched than the other San Venanzo volcanic rocks, coherently with its evolved liquid composition proposed here. Major and trace element contents indicate a general depletion proportional to the amount of CaO content. The negative trends in Harker-type diagrams with CaO as abscissa are compatible with a process of variable interaction between a silicate magma with sedimentary marly carbonates/limestones. The presence of Mg-rich (Fo97–92) and rim-ward CaO-enriched (up to 1.72wt%) euhedral olivine, as well as the presence of thin kirschsteinite rim around olivine crystals agree with a process of crustal carbonate assimilation by an originally strongly SiO2-undersaturated silicate magma. On the other hand, the lack of feldspars even in the rocks with the highest SiO2, the high CaO content, and the extreme SiO2-undersaturation of San Venanzo rocks exclude their derivation from a simple peridotitic source. In order to generate these peculiar compositions, the presence of a SiO2-K2O-CaO-rich H2O-bearing component, identified in a carbonatedphlogopiteperidotiteis required. The results of different isotopic systematics (Sr-Nd-Pb-He-Ne-Ar) presented here are compatible with a process ofcrustal contaminationboth atmantle sourcelevels (to explain the general N-S isotopic trends recorded in Quaternary volcanic rocks of Italianpeninsulaand Sicily) and with interaction of ultrabasic melts with limestones at shallow crustal depths.

The Miocene is a key interval in the geodynamic and oceanographic evolution of the Mediterranean marking the transition from a wide open basin to the modern closed basin. We used the Sr and Nd isotope records of two Miocene carbonate successions in the Adriatic to document that the evolution of the Mediterranean Basin controlled its seawater chemistry. During the late Aquitanian (similar to 21Ma), a time of glaciation and sea level lowstand, increased runoff affected the Sr isotope ratios of Mediterranean waters, whereas during the Burdigalian (20.44-15.97Ma) volcanism in the circum-Mediterranean area mainly influenced the Sr isotopic signature. During the Langhian (15.97-13.82Ma), a time of sea level highstand associated with the Middle Miocene Climatic Optimum, the Nd isotope values indicate that waters exchanged between the Paratethys and the Central Mediterranean. The Central Mediterranean was well connected with the Atlantic Ocean between the Langhian and the early Tortonian (15.97-11.5Ma), but exchange of water with the Paratethys declined. In the Messinian (6.3Ma), connections between some marginal Mediterranean basins, for example, the proto-Adriatic basin, and the Central Mediterranean, became restricted. In this basin, the Sr isotope values fell below the global reference line, while Nd isotope ratios show a strong affinity with the Atlantic Ocean and also indicate freshwater input. We conclude that the Mediterranean Nd isotope signature differs from that in the open oceans and reflects the basin physiography, reflecting a mix of signals derived from the adjacent oceans and local signals.

The 87Sr/86Sr isotope ratio has been widely used as a physical tool to date and correlate carbonate successions due to the long Sr residence time in comparison with the ocean mixing time. If this method works on oceanic successions, marginal basins may show different Sr isotope records in comparison with the coeval ocean one due to sea-level variations, continental run-off and restricted water exchanges. In this work, we present the 87Sr/86Sr isotope record of the upper Miocene carbonate ramp of the Lithothamnion Limestone (Majella Mountain, central Apennines), as an example of the onset of restricted water exchanges between a marginal basin and the ocean water masses. The overall latemost Tortonian-early Messinian Sr isotope record of the Lithothamnion Limestone fits below the global reference line. This deviation has been interpreted as due to the strong control that freshwater input and enhanced continental run-off, linked to the migration of the Apennine accretionary wedge and foredeep system, have had on the central Adriatic water chemistry. These results imply that an accurate oceanographic and geodynamic framework along with diagenetic overprint investigation has to be taken into consideration prior to apply SIS on carbonate successions on marginal basins, even when facies analyses indicate fully marine conditions. This seems to be the case for the upper Miocene Central Mediterranean carbonate successions, but may have more general validity and be extended to other recent or past marginal basins.

The late Miocene (11–9 Ma) volcanic rocks of Kef Hahouner, ~40 km NE of Constantine (NE Algeria), are commonly classified as lamproites in literature. However, these rocks are characterized by an anhydrous paragenesis with plagioclase and Mg-rich olivine phenocrysts, set in a groundmass made up of feldspars, pyroxenes and opaque minerals. Thus, we classify the Kef Hahouner rocks as ultrapotassic shoshonites and latites, having K2O N 3 wt.%, K2O/Na2O N 2.5, MgO N 3–4 wt.%, SiO2 b 55–57 wt.% and SiO2/K2O b 15. All the investigated samples showprimitive mantle-normalizedmulti-element patterns typical of orogenic (arctype) magmas, i.e. enriched in LILE (e.g. Cs, Rb and Ba) and LREE (e.g. La/Yb=37–59) with respect to the HFSE, peaks at Pb and troughs at Nb and Ta. Initial isotopic ratios are in the range of 87Sr/86Sr = 0.70874–0.70961, 143Nd/144Nd = 0.51222–0.51223, 206Pb/204Pb = 18.54–18.60, 207Pb/204Pb = 15.62–15.70 and 208Pb/204Pb = 38.88–39.16. The Kef Hahouner volcanic rocks show multi-element patterns similar to the other circum-Mediterranean lamproites and extreme Sr, Nd and Pb isotopic compositions. Nevertheless, the abundant plagioclase, the presence of Al-rich augite coupled with high Al2O3 whole rock compositions (9.6–21.4 wt.%), and the absence of phlogopite are all at inconsistentwith the definition of lamproite.Wereviewed the rocks classified as lamproites worldwide, and found that many of these rocks, as for the Kef Hahouner samples, should be actually defined as “normal” potassic to ultrapotassic volcanic rocks. Even the grouping of lamproites into “orogenic” and “anorogenic” types appears questionable.

The Elazig and Tunceli provinces in eastern Anatolia host a complex succession of Miocene-Pleistocene effusive and explosive volcanic rocks, divided into four distinct volcanic phases. The most abundant and widespread products are the calcalkaline Mazgirt volcanic rocks, characterized by wide Sr isotope variations (87Sr/86Sr ~0.7054-0.7077) and narrower 143Nd/144Nd (~0.51246-0.51260) and Pb isotopes (e.g., 206Pb/204Pb ~18.89-19.13). New 40Ar-39Ar ages indicate that Mazgirt volcanic activity occurred between ~16.3 and 15.1 Ma. The other three volcanic phases are represented by the Tunceli mildly alkaline basaltic lavas (~11.4-11.0 Ma), the Pliocene Karakocan (~4.1 Ma) and Pleistocene Elazig (~1.9-1.6 Ma) Na-alkali basaltic lavas with clear OIB-like geochemical signature.Mazgirt volcanics can be subdivided on the base of mode of emplacement into lava flows and lava domes units characterized by petrographic, chemical and isotopic differences: lava flows are calcalkaline, whereas lava domes mostly belong to a high-K calcalkaline series and are, on average, more LREE- and 87Sr-enriched. Lava domes are more porphyritic, with a phenocryst assemblage dominated by amphibole, whereas plagioclase and clinopyroxene are the most abundant phenocryst phases in lava flows, pointing out that evolution of dome magmas occurred in conditions of slightly higher pressure, favouring the crystallization of hydrous phases.The Karabakir Formation, previously reported as late Miocene- Pliocene, encloses Mazgirt volcanics and is capped by Tunceli basalts. These new age data constrain the Karabakir Formation emplacement from early to late Miocene.The evolution of this igneous activity mirrors the geodynamic framework of the region: the early-middle Miocene Mazgirt volcanics represent arc volcanism related to Eurasia-Arabia convergence. The late Miocene Tunceli basalts postdate the onset of post-collisional tectonics in Eastern Anatolia, whereas the Karakocan and Elazig volcanic rocks were emplaced after the initiation of strike-slip motion on the North Anatolian and East Anatolian Fault systems.

During Middle-earlyLate Triassic(∼243–235?Ma) a diffuse igneous activity developed in the Southern Alps (Italy). Sparselava flowand pyroclastic succession remnants of such Southern Alps Triassic Igneous Rocks (SATIR) crop out in the Brescian Prealps, the Vicentinian Alps (Recoaro-Schio-Posina), Non Valley, Dolomites and Julian Alps.Plutonic rocksare found in two main plutonic complexes (Monzoni and Predazzo) and a small stock (Cima di Pape). Coeval igneous products can be traced eastward to Austria and Dinarides, for a total length of ∼450?km. The coeval formation of major late Anisian-lateLadiniancarbonate platformsin the subsiding eastern Dolomites, and significant uplift and subaerial erosion in the western Dolomites suggest, for these areas, the occurrence of large-scale strike-slip andextensional tectonicswith the development of horst-and-graben structures. This study reports the first complete review of the SATIR activity, including new mineral chemical data on 14 samples, 61 major and trace element whole rock analyses and 7 Sr-Nd-Pbisotopic ratiosfor volcanic and plutonic samples from Dolomites (lavas plus Monzoni and Predazzo plutonic rocks) and Vicentinian Alps lavas. Despite the variable post-magmatic modifications, the large areal distribution of the products and their wide spectrum of chemical compositions, these samples show rather common geochemical and mineralogical characteristics and define major and trace element trends that can be associated with nearly close-system magmatic evolution. Minor uppercrustal contaminationscan be observed in specific cases, mostly in the most differentiated products (SiO2>70?wt%). A specific characteristic of SATIR is their calcalkaline to shoshonitic affinity, resembling the derivation from subduction-modifiedmantle sources, a feature at odds with the coeval strike-slip and extensional tectonics. Geochemical modelling, petrological considerations and geological constraints allow us to propose a model in which the SATIR mantle sources reflect previous subductionmetasomatism(likely occurred duringVariscantimes). These metasomatised mantle sources were reactivated ∼90–100 Myr after the end of the subduction, when continental rifting caused a raise of the geotherms and passive upwelling of asthenospheric mantle.

Leucite-bearing volcanic rocks are commonly found within and around the Mediterranean area. A specific type of this rock group are leucitites. They are found both in a hinterland position of active and fossil subduction systems as well as in foreland tectonic settings, but none have been found in the Maghreb (N Africa) and Mashreq (Middle East) areas. Here a review of the main leucitite occurrences in the circum-Mediterranean area is presented, with new whole-rock, mineral chemical and Sr-Nd-Pb isotopic ratios on key districts, with the aim of clarifying the classification and genesis of this rock type. Many of the rocks classified in literature as leucitites do not conform to the IUGS definition of leucitite (i.e., rocks with >10 vol% modal leucite and with foids/(foids + feldspars) ratio > 0.9, with leucite being the most abundant foid). Among circum-Mediterranean rocks classified as leucitites in the literature, we distinguish two types: clinopyroxene-olivine-phyric (COP) and leucite- phyric (LP) types. Only the second group can be truly classified as leucitite, being characterized by the absence or the very rare presence of feldspars, as well as by ultrapotassic composition. The COP group can be distinguished from the LP group on the basis of lower SiO2, Na2O + K2O, K2O/Na2O, Al2O3, Rb and Ba, and higher MgO, TiO2, Nb, Cr and Ni. The LP group shows multi-elemental patterns resembling magmas emplaced in subduction-related settings, while COP rocks are much more variable, showing HIMU-OIB-like to subduction-related-like incompatible element patterns. COP rocks are also characterized generally by more homogeneous isotopic compositions clustering towards low Sr and high Nd isotopic ratios, while LP leucitites plot all in the enriched Sr-Nd isotopic quadrant. LP rocks usually have lower 206Pb/204Pb and higher 207Pb/204Pb. This study shows that the geochemical signal of mantle melts does not always reflect the tectonic setting of magma emplacement, suggesting paying extreme attention in proposing geodynamic reconstructions on the basis of chemical data only.

Isla El Tigre volcano is located in the Gulf of Fonseca (Honduras) along the Central America volcanic front, where a significant change in the strike of the volcanic chain is observed. The studied samples of this poorly investigated volcano are mainly subalkaline basic to intermediate lavas (basalts and basaltic andesites) and subordinate subalkaline/alkaline transitional basalts, both having the typical mineralogical and geochemical characteristics of arc volcanic rocks. On the basis of petrographic and geochemical features, two groups of rocks have been distinguished. Lavas from the main volcanic edifice are highly porphyritic and hy-qz normative, and have lower MgO contents (< 5 wt.%). They show significant LILE and LREE enrichments and Nb-Ta depletions, and have a strong slab signature as well as incompatible element contents similar to those of the main front of the adjacent volcanoes in El Salvador and Nicaragua (e.g., Ba/La up to 80). In contrast, lavas from the parasitic cones have higher MgO contents (> 5 wt.%), are ol-hy normative and show lower HFSE depletions relative to LILE and LREE, with lower Ba/La, Ba/Nb and Zr/Nb ratios. This suggests that mantle-derived magmas were not produced by the same process throughout the activity of the volcano. The bulk rock geochemistry and 87Sr/86Sr (0.70373-0.70382), 143Nd/144Nd (0.51298-0.51301), 206Pb/204Pb (18.55-18.58), 207Pb/204Pb (15.54-15.56) and 208Pb/204Pb (38.23-38.26) isotopic data of Isla El Tigre compared with the other volcanoes of the Gulf of Fonseca and all available literature data for Central America suggests that this stratovolcano was mainly built by mantle-derived melts driven by slab-derived fluid-flux melting, while magmas erupted through its parasitic cones have a clear signature of decompression melting with minor slab contribution. The coexistence of these two different mantle melting generation processes is likely related to the complex geodynamic setting of the Gulf of Fonseca, where the volcanic front changes direction by ca. 30° and two fundamental tectonic structures of the Chortis continental block, mainly the N-S Honduras Depression and the NE-SW Guayape Fault Zone, cross each other.

This work was supported as part of Patrick Sugden's PhD studentship funded through the Leeds-York SPHERES NERC doctoral training partnership (NE/L002754/1). Part of the fieldwork and research was funded by the University of Leeds, the Carnegie Institution of Washington, the ERASMUS exchange programme (for IS) and the Science Committee of the Armenian Ministry of Education and Science (project #18T-1E368). The majority of the B isotope analytical work was supported by IGG-CNR funds P1600514. We present the first boron abundance and δ11B data for young (1.5-0 Ma) volcanic rocks formed in an active continent-continent collision zone. The δ11B of post-collisional volcanic rocks (−5 to +2‰) from the Armenian sector of the Arabia-Eurasia collision zone are heavier than mid-ocean ridge basalts (MORB), confirming trace element and isotope evidence for their derivation from a subduction-modified mantle source. Based on the low B/Nb (0.03-0.25 vs 0.2-90 in arc magmas), as well as low Ba/Th and Pb/Ce, this source records a subduction signature which is presently fluid-mobile element depleted relative to most arc settings. The heavier than MORB δ11B of post-collision volcanic rocks argues against derivation of their subduction signature from a stalled slab, which would be expected to produce a component with a lighter than MORB B, due to previous fluid depletion. Instead, the similarity of δ11B in Plio-Pleistocene post-collision to 41 Ma alkaline igneous rocks also from Armenia (and also presented in this study), suggests that the subduction signature is inherited from Mesozoic-Paleogene subduction of Neotethys oceanic slabs. The slab component is then stored in the mantle lithosphere in amphibole, which is consistent with the low [B] in both Armenian volcanic rocks and metasomatic amphibole in mantle xenoliths. Based on trace element and radiogenic isotope systematics, this slab component is thought to be dominated by sediment melts (or supercritical fluids). Previously published δ11B of metasediments suggests a sediment-derived metasomatic agent could produce the B isotope composition observed in Armenian volcanic rocks. The lack of evidence for aqueous fluids preserved over the 40 Myr since initial collision supports observations that this latter component is transitory, while the lifetime of sediment melts/supercritical fluids can be extended to >40 Myr. Publisher PDF

We report the results of a study on early Miocene to Pleistocene volcanic rocks cropping out west of the Karliova Triple Junction in Eastern Anatolia (Elazig, Tunceli, and Bingol provinces). Here the Eurasia-Arabia convergence resulted in collision, marked by the Bitlis-Zagros suture (similar to 13 Ma), followed by activation of the dextral transform North Anatolian Fault (NAF). At similar to 6 Ma the formation of the sinistral transform East Anatolian Fault (EAF) marked the separation of the Anatolian block, which became a kinematically independent plate. On the basis of petrographic, geochemical and Sr-Nd-Pb isotopic characteristics, as well as new Ar-40-Ar-39 age determinations, we distinguish three phases of activity: (1) early-middle Miocene (16.3-15.5 Ma) production of calc-alkaline basaltic trachyandesite to dacites in the Pertek and Mazgirt districts; (2) emplacement of late Miocene (11.4-11.0 Ma) transitional basalts in the Tunceli area; (3) emplacement of Plio-Pleistocene Na-alkali basalts in Karakocan (4.1Ma) and Elazig (1.7 Ma). The oldest samples are characterized by large ion lithophile element (LILE) enrichment (e.g. Ba/Nb = 32-76) with high Sr-87/Sr-86 (0.7052-0.7065) and low Nd-143/Nd-144 isotopic ratios (0.51246-0.51262). The late Miocene basalts display variable geochemical characteristics, including large variations in Sr-87/(86) Sr (0.7039-0.7068) and LILE/HFSE (high field strength element) ratios (e.g. Ba/Nb = 13-36). The Plio-Pleistocene alkali basalts have higher LILE and HFSE contents and lower LILE/HFSE ratios (Ba/Nb = 8-21) compared with the two previous groups, low Sr-87/Sr-86 (0.70330 0.7038) and high Nd-143/Nd-144 (0.51270-0.51290), with compositions similar to those of oceanic intraplate magmas. Pb isotopes vary slightly: Pb-206/Pb-204 ranges from 18.66 to 19.11, Pb-207/Pb-204 from 15.64 to 15.72 and Pb-208/Pb-204 from 38.67 to 39.24, with the calc-alkaline early-middle Miocene rocks characterized by higher Pb-207/Pb-204 and Pb-208/Pb-204 at a given Pb-206/Pb-204. The evolution of volcanic activity is strictly linked to the geodynamic scenario. The early-middle Miocene magmas, emplaced in a convergent setting, indicate derivation from mantle sources modified by subduction components, whereas the late Miocene Tunceli transitional basalts mark the change from compressional to strikeslip tectonics. During the development of the NAF and EAF, passive upwelling of the sub-slab mantle, favoured by the formation of small pull-apart basins, led to the onset of Na-alkali basaltic activity.

Tectonic mixing of slab- and mantle-derived materials at the interface between converging plates highly enhances fluid-mediated mass transfer from the slab to the overlying mantle. Subduction mélanges can provide information about the interaction among different slices accreted at plate interface domains, with implications on the tectonic and geochemical evolution of the plate-interface itself. At Cima di Gagnone, pelitic schists andgneissenclose chloriteharzburgiteandgarnetperidotitelenses, like in subduction mélanges located in-between downgoing slabs and overlying mantle. These peridotites host MORB-typeeclogiteand metarodingite, and derive from dehydration of serpentinized mantleprotoliths. Their enrichment in fluid-mobile B, As, Sb, U, Th is the result of an early-stage oceanicserpentinization, followed by interaction with hostmetasedimentsduring subduction burial. Here we define the element exchange process in the Gagnone mélange by means of the B, Sr and Pb isotope analysis of its main lithologies (ultramafic,mafic rocksand paragneiss). The87Sr/86Sr and206Pb/204Pb ratios ofultramafic rocks(0.7090–0.7124 and 18.292–18.837, respectively) show enrichments in radiogenic Sr and Pb after exchange with the host paraschist (up to 0.728787Sr/86Sr; 18.751206Pb/204Pb). The δ11B values of peridotites (down to −10‰) point to a combined effect of (1)11B release to deserpentinization fluids (serpentinized protoliths likely had positive δ11B and lower radiogenic Sr, Pb), and of (2) exchange with fluids from the surrounding metasediments. The whole Gagnone rock-suite is finally overprinted by retrograde fluids that essentially bring to an increase in radiogenic Pb (about 19.0206Pb/204Pb) and to values of 0.71087Sr/86Sr and of −10‰ δ11B. The recognition of different stages of interaction between mantle rocks and sedimentary/crustal reservoirs allows us to define the geochemical effects related to the early coupling of such rocks along the plate-interface. Our study shows that ultramafic rocks involved in subduction-zonemetamorphismand serpentinization uptake radiogenic Pb and Sr released by associated sedimentary reservoirs. The exchange process envisioned here is not only representative of subduction mélanges: it can also be a proxy of mass transfer between slab and serpentinized supra-subduction mantle, as occurs in forearcs. Dehydration of the Gagnone-type serpentinized mantle releases crust-derived components to arcs, without direct involvement of metasediment dehydration and/or melting in subarc environments. The retention of appreciable amounts of fluid-mobile elements, radiogenic Pb and Sr in dehydrated Gagnone peridotites has implications on element recycling in the deep Earth’s mantle.

Diplomazia2 is framed within the program "Science for Diplomacy: Multi-disciplinary Training Program", and it is the result of closer and more mature collaboration between the Directorate General for Cooperation on Development of the Ministry for Foreign Affairs and International Cooperation (MAECI), the Italian Agency for Cooperation on Development (AICS) and the National Research Council (CNR). The implementation of joint projects such as DIPLOMAzia2 highlights the effectiveness of the diplomacy-science partnership as the driving force behind the achievement of relevant goals jointly pursued by the international community.

The middle Miocene is an important time to understand modern global climate evolution and its consequences on marine systems. The Mid-Miocene Climatic Optimum (between 17·0Ma and 13·5Ma) was the warmest time interval of the past 35 million years during which atmospheric CO2concentrations were lower than today. In the Mid-Miocene Climatic Optimum, a significant carbon cycle perturbation occurred, expressed as a last long-term positive carbon isotope shift, known in literature as the Monterey Carbon Isotope Excursion and recorded in open-ocean settings. In this work, the lower to middle Miocene carbon isotope records from three different domains of the Central Mediterranean are analysed with the aim of identifying the local carbonate platform response to the major global carbon cycle perturbation of the Monterey Event. Carbon and oxygen isotope ratios have been measured on samples belonging to three different stratigraphic sections, two of them are representative of shallow-water settings (Latium–Abruzzi and Apula platforms), and the latter of a hemipelagic setting (Umbria–Marche Basin). A well-defined Monterey Carbon Isotope Excursion is recorded also in these shallow-water sections. Despite their expected problematic stratigraphic constraints, a reliable age model is provided by calcareous nannofossil biostratigraphy and strontium isotope stratigraphy. In both of the carbonate platform successions examined, the Monterey Carbon Isotope Excursion coincides with a spread of bryozoans over other carbonate-producing biota. The high productivity of the bryozoan-dominated factory in the aphotic zone had an important control on the platform depositional profile. The high rates of sediment production in the deeper aphotic and oligophotic zones produced a depositional profile of a low-angle ramp.

Recent geochemical work shows that subduction-zone serpentinites are repositories for fluid-mobile elements absorbed during interaction with sediment-derived fluids. Unraveling the geochemical fingerprint of these rocks helps to define timing of tectonic accretion of sediments along the subduction interface and the role ofserpentinitein element recycling tovolcanic arcs. Here we present the trace element andisotopic composition(B–O–H, Sr, Pb) of high-pressure serpentinites from the Voltri Massif (Ligurian Western Alps, Italy), to discuss their role as incompatible element carriers and their contribution to recycling of sediment-derived components in subduction zones. The serpentinites presented here record metamorphic olivine growth during eclogite-faciesmetamorphismand show undeformed and mylonitic textures. Field relations show that undeformed rocks are enclosed in deformed ones and that nometasedimentary rocksare present nearby. Undeformed serpentinite has very high δ11BSRM951(from +26‰ to +30‰), low Sr and Pbisotope ratios(87Sr/86Sr=0.7053–0.7069;206Pb/204Pb=18.131–18.205) and low As and Sb contents (0.1 and 0.01μg/g, respectively). Oxygen and hydrogen isotope compositions are +4.5‰ and −67‰, respectively. In contrast, mylonitic serpentinite shows lower δ11B (from +22‰ to +17‰), significant enrichment in radiogenic Sr and Pb isotopes (87Sr/86Sr up to 0.7105;206Pb/204Pb up to 18.725), and enrichment in As and Sb (1.3 and 0.39μg/g, respectively). δ18O of the mylonitic serpentinites reaches values of +5.9‰, whereas δD is comparable with that of undeformed rocks (approximately −70‰). In mylonitic serpentinites, the B and Sr isotopic values and the fluid-mobile element (FME) concentrations are near those for the Voltri metasedimentary rocks (calc- and mica-schists). Pb systematics also reveal influx of a crust-derived component. Our dataset shows that undeformed serpentinite still preserves an oceanic geochemical fingerprint, whereas mylonitic serpentinite is reset in its concentrations of FME and its B, Sr and Pb isotope compositions, due to interaction with sediment- and crust-derived fluids. The environment of this interaction is either compatible with (i) an outer-rise zone setting, withpercolationof seawater-derived fluids enriched in sedimentary components into bending-related fault structures, or with (ii) subduction channel domains, where ascending sediment-derived slab fluids infiltrate slices of former oceanic serpentinite accreted to the plate interface domain. Influx of sediment-derived subduction fluids along major deformation zones in serpentinite modifies the element budget of the rocks, with important implications for element recycling and the tectonic history of serpentinite. The B, Sr and Pb isotopic systematics, coupled with FME concentration in serpentinites are particularly helpful geochemical tracers of interaction between different reservoirs in subduction-interface environments, and are more sensitive than the traditionally applied stable oxygen and hydrogen isotope compositions.

After the studies of the '60s and '70s, a new collaboration between Turkish and Italian researchers started in 1995, which is still active. From 1995 to 2010 main target of this collaboration was Western Anatolia region. Main results were the setting up of a new geodynamic model for the Western Anatolian and Aegean Region, and a detailed description of the volcanic products outcropping all over Western Anatolia, where seven magmatic association with different geochemical characters were recognized, both with subduction-related or with intraplate-type affinity. Further studies, involving radiogenic isotope geochemistry as well as B-Li stable isotopes, allowed to better define the evolution of the mantle source of magmas, and to put further constraints on the geodynamic evolution of the region.

The history of research on Anatolia volcanism began in the early 60s of the last century and continued up to now. Early researches were published in 1966 and had as main topics the Central Anatolia. Subsequently, researchers from the University of Pisa studied the link between the volcanism of Western Anatolia and Aegean Sea region. Later researches shifted again towards the Central Anatolia and moved to the north-eastern region of Lake Van and the Kars plateau. All the collected data were merged in a review paper in 1982 (Innocenti et alii, 1982b), which summarized the evolution of Neogene Volcanism in Anatolia that constitutes a milestone and, mainly from a stratigraphic point of view, is largely still valid.

A diffuse Neogene-Quaternary volcanic belt crops out in Central and Eastern Anatolia. Since the early '60s, several Italian geologists, in collaboration with Turkish colleagues investigated many Anatolian sectors characterized by the presence of igneous activity. The main aim is to infer the causes of activation of their mantle sources in terms of local and global-scale geology constraining the time-space distribution of the the main products. Latest studies were first targeted on the Karacada? shield volcano (the Southeastern Anatolia), the biggest volcanic edifice of the whole circum-Mediterranean area, occupying an area in the order of 104 km2, on the Arabian plate foreland, characterized by alkali basaltic products with OIB-HiMu geochemical signature. Other studies, still in progress, highlight the occurrence of both orogenic and anorogenic products in three areas: Central Anatolia (from Konya to Sivas, including Kapadokya), SE Anatolia (around ?anl?urfa and Gaziantep), and the westernmost sector of Eastern Anatolia (between Elaz?? and Bingöl). An almost continuos shift from calc-alkaline igneous activity to mildly sodic alkali basaltic compositions, with some products with transitional affinity, is commonly recorded essentially only in the westernmost areas. On the other hand, in Central and SE Anatolia a clear temporal evolution of the erupted magmas in terms of important changes in major oxides, trace elements as well as Sr-Nd-Pb isotopic ratios is not recorded. Indeed here a largely overlapping (both in terms of space and time) "orogenic" and "anorogenic" products is commonly observed. On the other hand, calc-alkaline lavas clearly predate alkali basalts (with transitional products showing intermediate age) in Eastern Anatolia.

The Aegean rift is considered to be either a classic backarc basin, or the result of the westward escape of Anatolia, or the effect of a gravitational collapse of an over-thickened lithosphere. Here these models are questioned. We alternatively present a number of geodynamic and magmatic constraints suggesting a simple model for the genesis of the extension as being related to the differential advancement of the upper lithosphere over a heterogeneous lower African plate. The Greek microplate overrides the Ionian oceanic segment of the African plate faster than the Anatolian microplate over the thicker Levantine more continental segment. This setting is evidenced by GPS-velocity gradient in the hangingwall of the Hellenic–Cyprus subduction system and requires a zone of rifting splitting the hangingwall into two microplates. This mechanism is unrelated to the replacement of retreated slab by the asthenosphere as typically occurs in the backarc of west-directed subduction zones. The supposed greater dehydration of the Ionian segment of the slab is providing a larger amount of fluids into the low velocity channel at the top of the asthenosphere, allowing a faster decoupling between the Greek microplate and the underlying mantle with respect to the Anatolian microplate. Slab ruptures associated with the differential retreat controlled by the inherited lithospheric heterogeneities in the lower plate and the proposed upwelling of the mantle suggested by global circulation models would explain the occurrence and coexistence of slab-related and slab-unrelated magmatism.

In lavas spanning ~ 10Ma of subduction-related volcanism in Western Anatolia, we observe remarkably similar patterns of δ 7 Li and δ 11 B variation. In this setting, magmatism records a transition from calc–alkaline to ultrapotassic character, consistent with overall lower mean extents of melting, and a changing mantle source that reflects a fractionating, higher temperature slab input consistent with the gradual cessation of subduction. Subsequent rift-related intraplate magmatism record δ 7 Li signatures within the range observed for MORBs and OIBs, indicating an abrupt transition to a mantle source unmodified by subduction.

Over the last ~267 ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30 % of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K2O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An38–21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300 ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50–1532 ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO2 rhyolites may be a common process at the Aeolian volcanoes, as already attested for a variety of volcanic systems around the world., Contributions to Mineralogy and Petrology, 170 (5-6), ISSN:0010-7999, ISSN:1432-0967

On 15 October 2011, a submarine eruption offshore of El Hierro Island gave rise to floating volcanic products, known as xenopumices, i.e., pumiceous xenoliths partly mingled and coated with the juvenile basanitic magma. Over the last few years, no consensus in the scientific community in explaining the origin of these products has been reached. In order to better understand the formation of xenopumice, we present a textural, mineralogical, and geochemical study of the possible magmatic, hydrothermal, and pyrometamorphic processes, which usually operate in the plumbing systems of active volcanoes. We carried out a comprehensive SEM investigation and Sr-Nd-Pb isotope analyses on some samples representative of three different xenopumice facies. All the data were compared with previous studies, new data for El Hierro extrusives and a literature dataset of Canary Islands igneous and sedimentary rocks. In the investigated xenopumices, we emphasize the presence of restitic magmatic phases as well as crystallization of minerals (mainly olivine + pyroxene + magnetite aggregates) as pseudomorphs after pre-existing mafic phenocrysts, providing evidence of pyrometamorphism induced by the high-T juvenile basanitic magma. In addition, we identify veins consisting of zircon + REE-oxides + mullite associated with Si-rich glass and hydrothermal quartz, which indicate the fundamental role played by hydrothermal fluid circulation in the xenopumice protolith. The petrological data agree with a pre-syneruptive formation of the xenopumice, when El Hierro basanite magma intruded hydrothermally altered trachyandesite to trachyte rocks and triggered local partial melting. Therefore, the El Hierro xenopumice represents a snapshot of the transient processes at the magma-wall rock interface, which normally occurs in the feeding system of active volcanoes.

Boron isotope data are presented for Cenozoic Western Anatolia rocks, which define two main associations: (i) calc-alkaline, shoshonitic and ultra-potassic rocks (Early to Middle Miocene); and (ii) Late Miocene–Quaternary intraplate alkali basalts. Boron data, together with Sr-Nd isotope and other trace elements, are consistent with a progressive dehydration of the slab, producing fluid phases gradually depleted in B (and 11B). These fluids were added to the supraslab mantle, triggering a partial melting that gave rise to orogenic magmatism. The stretching and tearing of the slab caused by the faster convergence of Greece over Africa with respect to Anatolia facilitated an interaction of the upwelling subslab asthenosphere with residual slab-fluids during the Late Miocene followed by production of typical intraplate magmas during the Pleistocene–Holocene, whose relatively high delta11B (approximately -2‰) is considered representative of the local asthenosphere not affected by subduction contamination.

Serpentinites form by hydration of mantle peridotite and constitute the largest potential reservoir of fluid-mobile elements entering subduction zones. Isotope ratios of one such element, boron, distinguish fluid contributions from crustal versus serpentinite sources. Despite 85% of boron hosted within abyssal peridotite being lost at the onset of subduction at the lizardite-to-antigorite transition, a sufficient cargo of boron to account for the composition of island arc magma is retained (c. 7 mu gg(-1), with a delta B-11 of + 22%) until the down-going slab reaches the antigorite-out isograd. At this point a B-11-rich fluid, capable of providing the distinctive d11B signature of island arc basalts, is released. Beyond the uniquely preserved antigorite-out isograd in serpentinites from Cerro del Almirez, Betic Cordillera, Spain, the prograde lithologies (antigorite-chlorite-orthopyroxene-olivine serpentinite, granofels-texture chlorite-harzburgite and spinifex-texture chlorite-harzburgite) have very different boron isotope signatures (delta B-11 - -3 to + 6%), but with no significant difference in boron concentration compared to the antigorite-serpentinite on the low P-T side of the isograd. B-11-rich fluid, which at least partly equilibrated with pelagic sediments, is implicated in the composition of these prograde lithologies, which dehydrated under open-systemconditions. Serpentinite-hosted boron lost during the early stages of dehydration is readily incorporated into forearc peridotite. This, in turn, may be dragged to sub-arc depths as a result of subduction erosion and incorporated in a melange comprising forearc serpentinite, altered oceanic crust and pelagic sediment. At the antigorite-out isograd it dehydrates, thus potentially providing an additional source of B-11-rich fluids. (C) 2014 Elsevier B.V. All rights reserved.

Ultramafic rocks recovered from Hole 1268a, Ocean Drilling Program Leg 209, to the south of the 15°20′N Fracture Zone on the Mid-Atlantic ridge have experienced a complex history of melt depletion and subsequent interaction with a series of fluids under varying temperature and pH conditions. After intense melt depletion, varying degrees of serpentinization at 100–200 °C took place, initially under seawater-like pH conditions. Subsequently, interaction with a higher temperature (300–350 °C) fluid with low (4–5) pH and low MgO/SiO2 resulted in the heterogeneous alteration of these serpentinites to talc-bearing ultramafic lithologies. The proximity of the currently active, high temperature Logatchev hydrothermal field, located on the opposite flank of the Mid-Atlantic ridge, suggests that unlike more distal localities sampled during ODP Leg 209, Hole 1268a has experienced Si-metasomatism (i.e. talc-alteration) by a Logatchev-like hydrothermal fluid. Serpentinite strontium isotope ratios were not materially shifted by interaction with the subsequent high-T fluid, despite the likelihood that this fluid had locally interacted with mid-ocean ridge gabbro. 87Sr/86Sr in the ultramafic lithologies of Hole 1268a are close to that of seawater (c.0.709) and even acid leached serpentinites retain 87Sr/86Sr in excess of 0.707, indistinguishable from Logatchev hydrothermal fluid. On the other hand, boron isotope ratios appear to have been shifted from seawater-like values in the serpentinites (δ11B = c.+40‰) to much lighter values in talc-altered serpentinites (δ11B = +9 to +20‰). This is likely a consequence of the effects of changing ambient pH and temperature during the mineralogical transition from serpentine to talc. Heterogeneous boron isotope systematics have consequences for the composition of ultramafic portions of the lithosphere returned to the convecting mantle by subduction. Inhomogeneities in δ11B, [B] and mineralogy introduce significant uncertainties in the prediction of the composition of slab fluids released during the early- to mid-stages of subduction.

The Estancia Glencross Area (EGA) volcanic rocks form a series of five isolated buttes located at the southern end (∼52°S) of the discontinuous belt of Cenozoic basaltic lava formations occurring in the extra-Andean Patagonia. EGA volcanics are subalkalinebasaltsand basalticandesiteserupted at 8.0–8.5 Ma in a region closely behind the Andean Cordillera. EGAvolcanismpredated by about 4–5 my the onset of the volcanism in the nearby Pali Aike Volcanic Field, which produced highly primitive, alkaline lavas. Incompatible trace-element distributions and Sr–Nd isotope compositions of EGA rocks are those typical of within-plate OIB-type basalts and are indicative of minimal interaction of sub-lithosphericmagmaswith enriched reservoirs. The geochemical characteristics of EGA volcanics, as well as their age and location are consistent with a model of slab window opening beneath this region. The high silica content and thegarnetsignature of the estimated EGA primary magma are explained by a two-stage process involving the initial production of melts from a garnetlherzolitesource followed by the reaction of these melts withharzburgitecountry rocks during their ascent through the mantle lithosphere. The melt/harzburgite reaction, favoured by a slow melt ascent rate, as well as the low magma production at EGA, are likely related to the dominantly compressive stress regime operating in this area during LateMiocene.

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.