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19 pages, 15 figures, 2 tables, supplementary material https://doi.org/10.1016/j.margeo.2020.106372.-- Data availability: The datasets analysed during the current study are available from the corresponding author on reasonable request, The upper continental slope offshore Capo Vaticano (southern Tyrrhenian Sea) is characterized by a contourite depositional system with well-developed elongated sediment drifts. This system is related to a northward paleo-bottom current, similar to the present-day modified-Levantine Intermediate Water (modified-LIW) flowing from the Messina Strait. In this work, we show results from an integrated analysis of descriptive oceanography, high-resolution seismic profiles and core data (i.e., grain size, foraminiferal assemblages, tephrostratigraphy and AMS radiocarbon dating) collected from the crest and moat sectors of drift deposits. The studied succession formed since the mid Holocene, under the action of the modified-LIW and the stratigraphic architecture indicates an upslope migration of the moat and rather stable position of the crest sector. Grain-size features recorded from two sediment cores indicate the occurrence of a succession of complete bi-gradational sand-rich contourite sequences. Sandy facies were observed both as lag deposits formed in active moat channel and as coarser intervals of bi-gradational sequences forming drift deposits close to its crest. Their occurrence would highlight that upper slope environments impacted by intermediate water masses and proximal to sandy sources may represent favorable settings for accumulation of sandy sediment. The moat sector is characterized by a more complex stratigraphic record, where either moat sedimentation or lateral deposition of finer sediment occur, suggesting that further investigation is required to better understand this complex element of contourite systems. Based on available age information, some of the bi-gradational sequences probably formed during the Dark Age Cold Period, providing example of a small-scale cyclicity of contourite deposition, likely related to short-term (possibly multicentennial scale) fluctuations of the paleo modified-LIW. According to age constraints and analysis of foraminiferal assemblages, these fluctuations were likely governed by climate variations, with a weaker activity during warmer periods and faster currents during colder events, Core LGT5 was collected during the Gioia77 cruise funded by the Eurofleets2 Project. With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

In the Tyrrhenian back-arc basin, the Ventotene Volcanic Ridge (VR) represents a NW-SE-oriented morphological high, located 25 km north of Ventotene Island in the Eastern Pontine Islands. It is considered part of an alignment of volcanic edifices developed in the central-eastern Tyrrhenian Sea, from the western Pontine Islands (WPI) to the Campanian Volcanic Region. The samples dredged along the VR are basalts to trachybasalts belonging to the transitional (TR) rock-series, with a Ar-Ar age of 2.760 ± 0.039 Ma. Petrological and geochronological data link the VR basalts to the TR peralkaline rhyolites cropping out at the WPI (~1.6-1.1 Ma); here, during a time span of ~4.5-1.0 Ma highly differentiated products of high-potassium calc-alkaline (HKCA, ~4.5-2.9 Ma) and K-alkaline (KA, ~1 Ma) series were also erupted. Notably, the parental melts of the three rock-series were recognized in the continental slope close to the WPI (TR, HKCA) and eastward, namely in eastern Pontine Islands (KA), at the VR (TR), and in the Campanian Plain (HKCA). All the parental melts show typical orogenic geochemical signatures being originated from a similar heterogeneous suprasubduction mantle source, without the involvement of anorogenic sources. Tectonically, the faults bordering the VR, associated to the Pliocene E-W directed rifting stage of the Tyrrhenian back-arc basin were characterized by a more intense activity during the time span ~5.0-2.0 Ma (the emplacement time of HKCA and TR series), while KA products are related to a later stage of extension deformation (

Tourmalines from the late-Variscan Arbus pluton (SW Sardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mossbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges from schorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na + Fe2+ ↔ □ + Al, which relates schorl to foitite. The homovalent substitution (OH) ↔ F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2+ + (OH, F) ↔ Al + O relates schorl/fluor-schorl to oxy-schorl. Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite + quartz → schorl + quartz → fluor-schorl + quartz → foitite + quartz. The schorl → foitite evolution represents a distinct trend towards (Al + □) increase and unit-cell volume decrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other Li-minerals in the Arbus pluton. Tourmaline-bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle-upper crust.

Discoveries from multibeam bathymetry and geochemical surveys performed off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water ( 250 m) that host pockmarks, mounds, small cones and active fluid vents, and which are interpreted as complex fluid escape features developed both through vigorous-explosive events and steady seepage. Their spatial distribution suggests that the NE-SW trending faults bounding the Ponza-Zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids. Moreover, we performed a detailed geochemical study to investigate the source of the hydrothermal fluids. The geochemical signature of the collected fluids provides information of active CO2-dominated degassing with a significant contribution of mantle volatiles, with measured 3He/4He values > 3.0 Ra that are similar to those recorded at Stromboli and Panarea volcanoes. The hydrothermal system produces volatiles that may originate from residual magma batches, similar to the Pleistocene trachytes cropping out in the SE sector of Ponza Island, that were probably intruded in the shallow crustal levels and never erupted. The discovery of the Zannone hydrothermal field updates the record of active hydrothermal areas of the Mediterranean Sea. Moreover, the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the Mediterranean Sea.

An inclusive study of tourmaline, a well-known petrogenetic indicator, allowed the reconstruction of late-stage evolution of B-bearing Variscan granodioritic magmas in Sardinia batholith (Italy). Tourmaline samples from Mandrolisai igneous massif were chemically and structurally investigated by electron microprobe analysis, single-crystal X-ray diffraction, Mossbauer, infrared and optical absorption spectroscopy. Tourmaline aggregates occur both as large crystals displaying graphic textures with quartz, in aplite layers and pegmatite dykes within tonalitic granodiorite, and as fine-grained assemblages, in tourmalinite veins crystallized along fractures within metamorphic country rocks. Tourmaline was identified as schorl in pegmatites and as dravite in veins, both with relevant foitite and magnesio-foitite components. Petrological and mineralogical constraints based on mineral oxythermobarometry and tourmaline crystal chemistry converged towards crystallization temperatures in the range 650–400 °C at about 2.2 kbar, under NNO conditions that remained almost unvaried during the whole magma crystallization path. In the reconstructed scenario, Mandrolisai tourmaline recorded the late stages of consolidation of a single granodioritic magma batch, whose crystallization path locally led to residual concentration of B in the melt. Due to melt/hydrous fluid immiscibility processes, B enrichment promoted the crystallization of the large tourmaline + quartz assemblages in pegmatites. Late B-bearing fluids triggered metasomatic reactions and favored the precipitation of fine-grained tourmaline in tourmalinite veins under a brittle solid-state regime, which overprinted a fracture network of the country rocks previously formed under magmatic flow conditions. Mandrolisai granodiorites are metaluminous (ASI = 0.93–0.95), that is far from the compositional characters of typical B-bearing magmas, mostly felsic and markedly peraluminous (ASI > 1.2). The uncommon occurrence of tourmaline-bearing rocks in Mandrolisai may be an evidence of the limited control exerted by Al2O3 saturation on the origin of tourmaline. Conversely, a more important role of B contents, likely coming from crustal sources, may be invoked for tourmaline saturation in the magma.

The Zannone Giant Pockmark (ZGP) is a shallow-water (&lt, &minus, 150 m) giant depression located on the shelf off Zannone Island (Pontine Archipelago, central Tyrrhenian Sea, Italy), hosting active hydrothermal vents. The ZGP seabed displays different fluid-venting morphologies (pockmarks, lithified pavements, mounds, and cone-shaped structures) and widespread bacterial communities. In this study, we analyzed ROV (Remote Operated Vehicle) images to gain information on seabed geology and the textural, mineralogical, and geochemical composition of authigenic crusts and gravel-sized clasts sampled close to active emissions. ROV images show authigenic dome-shaped crusts composed of native sulfur associated with barite, gypsum, amorphous silica, and secondary hydrothermal minerals (illite&ndash, montmorillonite). The gravel-sized clasts are mostly rhyolites strongly affected by hydrothermal alteration (Alteration Index &gt, 88, depletion of some mobile elements and enrichment of some base metals), causing feldspar-destruction, silicification, formation of hydrothermal phyllosilicates, and precipitation of disseminated pyrite. More intense alteration implying the complete obliteration of the primary mineralogy or fabric is represented by quartz-pyrite samples. ZGP seabed morphology and petro-geochemical features of deposits point to the possible occurrence of a sulfide system linked to the degassing of magma similar to that feeding the Pleistocene products of Ponza Island.

In the present work, we report the chemical composition of representative emerald crystals from some of the most important worldwide deposits. Major and trace elements were investigated using Electron Microprobe Analysis (EMPA) and Secondary Ion Mass Spectrometry (SIMS) techniques. Binary, ternary and spider diagrams along with statistical analysis, i.e., Principal Component Analysis (PCA), were used to discriminate each deposit with high reliability. PCA of SiO2, Al2O3, V, Sc, B, Li content identified distinct groups. The use of binary and ternary diagrams contributed to discriminate among emerald crystals from various deposits, which are included in the same clusters of the PCA analysis. In addition, the geochemical features of each group were linked to the geological environment and genetic processes which leaded to emerald formation. In particular, the emeralds related to granitic-pegmatitic intrusions (Type-1) or those occurring in environments controlled by tectonic events (Type-2) were distinguished using the concentrations of major and trace elements. The results of this study can contribute to improve the existing genetic models and classification schemes as well as to identify useful geochemical fingerprints for provenance purposes.

The characterisation of the late Variscan intrusion of Monte Linas (southern Sardinia) allowed to firstly study some Sn-bearing ores of this area and their relationships with the surrounding intrusives. The Monte Linas pluton was emplaced at ca. 290 Ma at a shallow crustal level between allochthonous units and the foreland of the Sardinian Variscan belt. The pluton emplaced in a post-collisional regime into a previously exhumed low-grade basement, forming a coarse-grained monzogranite that is capped by an almost continuous sub-horizontal sheet of fine-grained rocks. The rocks within the pluton are ferroan F-bearing granites, belonging to the ilmenite-series. They have alumina saturation index values indicative of sub-aluminous to slightly peraluminous granitoids, as also indicated by the chemical composition of biotite within the pluton. The new data of this study indicate that the Monte Linas pluton formed from water-undersaturated magmas under low-fO2 conditions at temperatures > 850 °C. The later stages of magmatism were characterised by boiling and fluid expulsion at confining pressures of < 1 kbar, producing fayalite-bearing pegmatites, miarolitic facies and greisening. A wide variety of mineral deposits are associated with the Monte Linas pluton, including different types of Sn-bearing and Mo-bearing ores. Sn-bearing ores are represented by 1) Sn-As and Sn-Pb-Zn-Cu veins, and 2) "wrigglite" skarn Fe-Zn-Sn ores. Field and analytical studies, including fluid inclusion analyses, EMPA and SEM-EDS, allow to refer these deposits to the evolution of initial highly saline, hypothermal magmatic fluids, as confirmed by parageneses and fluid inclusion analyses of cassiterite in veins, which provide evidence of polyphase processes that started at temperatures close to 400 °C. The hydrothermal systems were initially characterised by low-fO2 and high-chlorine solutions that mobilised Sn and underwent rapid changes in physicochemical conditions that led to the deposition of cassiterite. In the "wrigglite" F-rich genetic environment, a role of fluoride as complexing agent for Sn can be inferred. The Monte Linas pluton is also characterised by Mo deposits, not typical in ilmenite series granites; they occur both as greisens and veins. Mo was mobilized as a result of rapid increases in fO2 within the magmatic system, and precipitated in a fS2-rich environment nearby the contact between the intrusion and the surrounding country rocks. The variety of Sn mineralising events around the Monte Linas pluton confirms the role of physicochemical characters of magmas and of magmatic processes in the genesis of tin deposits. The occurrence in southern Sardinia of a wide suite of ilmenite-series ferroan granites emplaced in similar geological contexts allows to consider the idea of a low-grade tin province and opens the way to further explorations.

Until now, the use of trace elements to discriminate among differing provenances of classical white marbles from Mediterranean areas have produced controversial results, and the many drawbacks of this approach have been widely discussed. The behavior of trace elements was tested, aiming to determine their effectiveness for provenance purposes. In this work, in particular, representative specimens of fine-grained white marbles from quarries at Carrara, Penteli, Paros, Afyon and Goktepe were analyzed by Laser Ablation ICP-MS. LA-ICP-MS is recent analytical technique, which allows high-precision measurement of a large number of elements in given points in solid samples without any pre-treatment. The results and their statistical treatment showed that many elements, such as Mn, Y, V, Pb and Th, can be used as interesting markers in that they can identify marbles from different sites. In addition, other elements may be useful in singling out one specific quarry district, such as Zr for Paros, Sr for Goktepe or Mg for Carrara. Trace elements determination may be very promising as a method of assigning unknown marble artifacts to a clearly identified quarry and LA-ICP-MS analytical technique may partly solve the problem of incomparability of the data published in past studies.

Mortars from the walls of S. Maria di Cerrate Abbey (South Italy) ranging in age from the 12th to the 20th century, were studied using a multidisciplinary approach designed to produce a guideline of investigation that can be applied to the knowledge and preservation of archaeological sites. The analyses highlighted the differences between medieval and post-medieval mortars; the former showed a dominantly carbonate aggregate, the latter a mostly siliciclastic aggregate. Among these, mortars dated from the XVI–XVII centuries display a mixed siliciclastic-carbonate binder whereas mortars from the XIX–XX centuries exhibit a predominantly carbonate binder with the Al-silicates mostly gathered as lumps.

Chiocci, Francesco L. ... et. al.-- 6 pages, 2 figures, High-resolution morpho-bathymetric data at 1:200,000 scale obtained during the FAIVI cruise (2011) and the resulting geomorphologic map of the Terceira island offshore area (central Azores, Portugal) are presented for the first time. The uneven morphology around Terceira is primarily related to volcanic features, such as linear and cone-shaped eruptive centres and lava flows. Such features are mostly concentrated on volcanic ridges and are aligned along preferential axes, suggesting a strong interaction between tectonics and volcanic processes. The occurrence of active tectonics is also demonstrated by systems of faults cutting the seafloor to the north, east and south of the island. Mapped erosive-depositional features include an insular shelf located at < 150 m water depth (wd), small landslide headwalls, erosive scarps, channelized features and crescent-shaped bedforms. The presented map may represent the base for a first-order geo-hazard assessment. © 2013 Copyright D. Casalbore

Rock samples dredged offshore the Pontine Archipelago (400–2000 m water depth) were studied by palaeontological analyses of planktic foraminifera and endo-epilithozoan faunas colonising Fe–Mn crusts and by petrographic analyses of volcanic samples. Palaeontological and petrographic analyses have revealed a complex Plio-Pleistocene depositional history controlled by hemipelagic sedimentation and volcanic activity with episodic non-depositional phases. The sedimentary deposits are associated with ferromanganese hardgrounds, more or less colonised by endolithic and epilithozoan organisms. The presence of foraminifera typical of tropical and subtropical waters (such as Globigerinoides ruber , Globigerinoides trilobus , Pulleniatina obliquiloculata and Sphaeroidinella dehiscens ) indicates that the micritic deposition occurred during warm climatic periods, whilst micrite cementation and hardground formation are here attributed to colder climates. The depositional processes recognised on the Pontine continental slope reveal a sediment-starved condition that locally resemble those of seamount environment. The slope sedimentation found in the Pontine Archipelago can be helpful in the interpretation of ancient deposits from seamounts and continental slope depositional environments, characterised by hardground and hiatuses.

Crystals of beryl from miarolitic pockets, hosted in pegmatitic dikes on the Island of Elba, in Italy, were analyzed for the major and minor elements, including the light elements, by EMPA and SIMS techniques. Back-scattered electron (BSE) images and X-ray maps were used to define the complex textures of these crystals and to highlight the pattern of element distribution in each sample. The majority of the analyzed crystals exhibit a complex pattern of zoning caused by changes in the chemical composition, which follow the main mechanisms of substitution defined for the crystal chemistry of beryl. The following main features are illustrated: (1) the occurrence of crystals with octahedral-site or tetrahedral-site substitutions in different domains of the same crystal, (2) the occurrence of crystals with exclusively tetrahedral or exclusively octahedral substitutions, and (3) the occurrence of crystals or crystal domains having a limited extent of octahedral-site and tetrahedral-site substitutions. However, the analytical data confirm the presence of a gap between the two series, having octahedral-site or tetrahedral-site substitutions. The observed enrichment in Cs and Li is strictly related to the geochemical and petrological features of the LCT host pegmatites. The presence of Ca in some beryl crystals in pegmatites emplaced in carbonate rocks suggests an interaction of the late hydrothermal fluids with country rocks. An enrichment in Fe could also be ascribed to the circulation of fluids having such a contaminant element attributed to the contribution of country rocks or the destabilization of early-crystallized Fe-rich minerals.

New high-resolution geophysical data collected along the eastern margin of the Tyrrhenian back-arc basin, in the Pontine Islands area, reveal a ~NW-SE elongated morphological high, the Ventotene Volcanic Ridge (VR), located on the northern edge of the Ventotene Basin. High-resolution multibeam bathymetry, combined with magnetic data, multi- and single-channel seismic profiles, and ROV dives, suggest that VR results from aggregation of a series of volcanic edifices. The summit of these volcanoes is flat and occurs at about 170 m water depth. Given their depths, we propose that flat morphologies were probably caused by surf erosion during Quaternary glacial sea level lowstands. Seismic stratigraphy together with magnetic data suggest that the volcanic activity in this area is older than 190-130 ka age and may be coeval with that of Ventotene Island (Middle Pleistocene). The submarine volcanoes, located 25 km north of Ventotene, are part of a ~E-W regional volcanic alignment and extend the Pontine volcanism landward toward the Gaeta bay. Integration of structural data from multichannel seismic profiles in this sector of the eastern Tyrrhenian margin indicates that several normal and/or transtensional faults, striking WNW-ESE, NNW-SSE, and NE-SW, offset the basement and form alternating structural highs and depressions filled by thick, mostly undeformed, sedimentary units. Arc-related magmatism is widespread in the study area, where the VR is placed at the hangingwall of the west-directed Apennines subduction zone, which is undergoing tensional and transtensional tectonics. Bathymetric and topographic evidence shows that VR lies in between a major NE-SW trending escarpment east of Ponza and a NE-SW trending graben southwest of the Roccamonfina volcano, a NE-SW transfer zone that accommodate the extension along this segmented portion of the margin. This suggests that the interaction between NE-SW and NW-SE trending fault systems acts as a structural control on location of eruptive centers, given that main volcanic edifices develop along the NW-SE direction, compatible with the extensional setting of the Tyrrhenian basin.

Water–rock interaction experiments have been performed to investigate the production of CO 2 -rich gas in the deep reservoir of the geothermal system of Mt Amiata (Italy) through the interaction between a natural phyllite sample (coming from 1115 m below ground level and considered representative of the deep reservoir) and a coexisting fluid phase. Experiments were conducted with an externally heated pressure vessel, a chamber furnace and a stirred micro-reactor at 300 °C and at P up to 35 MPa, using different solid/liquid ratios, and also under nominally anhydrous conditions. Experimental results show that CO 2 -rich gases containing variable amount of CO, CH 4 and other aliphatic and aromatic hydrocarbons were produced by fluid–rock interaction. Compositional data of the gas, coupled with solid residua characterization, show that thermal decomposition of magnesian siderite in phyllite is the process responsible for the gas genesis. This process is particularly effective when aqueous solutions interact with phyllite and it may represent the thermometamorphic reaction mainly responsible of the production of CO 2 -rich gas under hydrothermal conditions similar to those of the main reservoir in the Mt Amiata geothermal area.

The present study shows the preliminary micropalaeontological results obtained from surface samples collected during an Eurofleet marine geological survey in the Terceira offshore (Azores Archipelago, Portugal) carried out in September 2011.Benthic foraminiferal assemblages were studied in order to obtain a sea-floor ecological characterisation in natural stressed environments like active volcanic area of the Azores Islands. Sediments were collected at water depths ranging between 260 and 410 m and consist of blackish, sand-sized glass shards, in which highly vesicularto scoriaceous clasts prevail on fluidal striated fragments. All samples were stained with Rose Bengal to determine living and dead assemblages.The dominance of living specimens suggests that the first generation of foraminiferal colonisers was found. Diversity index (α-Fisher index), Faunal density and Foraminiferal Abnormality Index (FAI) were calculated to assess the structure of the assemblage and the degree of environmental stress. Living and dead assemblages are verysimilar; they are very scarce but sufficiently diversified. The living benthic assemblage is dominated by epi/shallow infaunal species Angulogerina angulosa and typical infaunal taxa like Bolivina spp.Subordinately other epifaunal (Ehrenbergina bradyi, Lenticulina spp., Quinqueloculina seminula, Stomatorbina concentrica) and agglutinated species (Ammoglobigerina globigeriniformis, Eggerelloides scabrus, Haplophragmoides canariensis, Spiroplectinella wrightii, Textularia spp.) are also recorded. Significant frequencies of specimens showing signs of test decalcification were found. These test alterations could be due to hydrothermal fluids, since similar features were recorded in foraminiferal specimens coming from other volcanic substrates in the Aeolian Arc (Tyrrhenian Sea). The dominance of living and dead A. angulosa specimens allows us to consider this species as opportunistic pioneer taxon able to colonise stressed environments. This is confirmed also by the highest values of FAI (>2%), recorded in most of the samples, indicating a persisting environmental stress. Angulogerina angulosa and Bolivina spp. are the species showing more abundant deformed specimens (irregular development of chambers and aberrant tests). On the basis of our observations, the recolonisation process and the spatial distribution patterns are strongly influenced by the sea bottom high hydrodynamic regime which is responsible for volcanic deposit transport and depositional events. These conditions may be reflected on the relationship between benthic foraminifers and substrate features, which are mainly restricted to grain size, morphology and texture of volcanic shards.

Marble quarries exploited in antiquity of the Denizli and Karacasu Basins (Turkey) were characterized by their petrography, carbon and oxygen isotopes, and cathodoluminescence. This study is an useful contribution for provenance studies of archeological artifacts composed of unknown marble. Marble quarries from the Hierapolis, Laodikeia, and Aphrodisias territories were considered; they constitute a homogeneous group of marble extraction districts. Collectively, they were among the most important sites for marble exploitation throughout antiquity from southwestern Anatolia, where only Afyon and Ephesus, which have already been studied extensively, were more important. In spite of that, the exportation of these marbles in ancient times has not yet been demonstrated. This is partially because their identification has never been fully addressed scientifically. Petrography, isotopes, and cathodoluminescence techniques used together are effective in discriminating among the study marbles. This could facilitate the determination of the provenance of these marbles in local monuments and artifacts. However, it could be difficult to determine the marble provenances in cases where a larger set of possible provenances should be taken into consideration.

Controlled cooling experiments at atmospheric pressure and fO2 of the NNO buffer were performed on three Stromboli lavas of calcalkaline (CA), high-K calcalkaline (HKCA) and shoshonitic (SHO) affinities. The experiments were conducted at cooling rates of 900 °C/h (fast cooling rate—FCR) and 1 °C/h (slow cooling rate—SCR), respectively, to investigate the kinetic factors governing textural and compositional features such as phase growth morphology, phase relations and phase compositions. The experiments produced different types of textures as both the cooling rate and the quenching temperatures were varied. In general, FCR experiments show a decrease of crystal size as well as a change in crystal shape from euhedral, to granular, to skeletal up to dendritic morphology with decreasing temperatures. SCR experiments produce less variable crystal size and crystal morphology. Measurements of plagioclases indicate that the crystal size and calculated crystal growth are functions of cooling rate; crystal growth rates are about two orders of magnitude higher in FCR experiments than SCR ones. Such textural responses are in agreement with the empirical calibration based on the plagioclase size dependence on cooling rate developed by Cashman (1993) . Experimental phase relations display three main features of the crystallization process: (1) the delay in the crystallization of the liquidus phase in the FCR experiments with respect to the SCR ones; (2) crystallization, controlled by the multiphase cotectic relations (plagioclase + pyroxenes ± olivine), is more enhanced for FCR experiments compared to that of SCR ones at the lowest experimental temperature (1100 °C); (3) crystallization of augite and pigeonite is sensitive to cooling rate and system compositions; pigeonite, not found in the natural rocks, crystallizes in the CA sample across SCR and FCR runs, and in the HKCA sample just in the SCR experiments. FCR and SCR experiments produce similar liquid lines of descent for both CA and HKCA starting materials suggesting that the processes of nucleation and growth play reciprocal roles through mass balance as cooling rate varies. This is not true for the SHO composition where the trends of melt composition appear to be especially influenced by the different amounts of olivine crystallization at the different cooling rates. Data on mineral compositions show that plagioclase and clinopyroxene are the phases more strongly affected by the cooling gradients; crystals from SCR experiments and, to a lesser extent, from FCR experiments, show zoning patterns mainly at the lowest experimental temperature.

Volcanic rocks on Ponza Island (Tyrrhenian Sea, central Italy) consist of Pliocene submarine rhyolites and Pleistocene subaerial trachyte and comendite lavas. Chemical variations and the homogeneous Sr and Nd isotopic signatures within the analyzed Pliocene rocks are ascribed to crystal fractionation. The absolute isotopic values, however, indicate the important role of a crustal component in the origin of these magmas. The very high-silica rocks were probably derived from a superimposed mechanism which may have been connected to the ascent of hydrothermal magmatic fluids.

High-resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the Pantelleria volcanic complex. This submarine eruption has been documented mainly by historical reports, describing basaltic scoria bombs floating on the sea surface (i.e., lava balloons). In this study, the 1891 eruptive vent has been identified as a small cone (volume of ∼700,000 m3) rising ∼90 m from 350 m w.d., and located within a newly discovered submarine volcanic field covering a wide area offshore from the NW coast of Pantelleria; recently, Kelly et al. (2012) confirmed this location by a multibeam and ROV survey. Pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts (i.e., small bombs, bomb fragments, and lapilli) and glass ash-sized grains; both have been characterized in their morphology, textures, and geochemistry. The distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes; these characteristics, along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to Hawaiian fountaining. Glass grains from a buoyant plume were dispersed northward from the vent, up to distances of 1.5 km, redirected by the Levantine Intermediate Water. The identification of the 1891 submarine eruptive vent offshore Pantelleria, as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow-intermediate depths and, among these, of the rare eruptions producing lava balloons.

[object Object]The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal structure refinement and electron microprobe analysis. All crystals are characterized by a dominance of Al Cr substitution with minor evidences of Mg Fe2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the MAl+TMg TAl+MMg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due to the higher concentration in Fe3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.

A general description of Mesozoic and Tertiary (Fortaleza) Brazilian alkaline and alkaline-carbonatite districts is presented with reference to mineralogy, petrology, geochemistry and geochronology. It mainly refers to scientific results obtained during the last decade by an Italo-Brazilian research team. Alkaline occurrences are distributed across Brazilian territory from the southern (Piratini, Rio Grande do Sul State) to the northeastern (Fortaleza, Ceara State) regions and are mainly concentrated along the borders of the Parana Basin generally coinciding with important tectonic lineaments. The most noteworthy characteristics of these alkaline and alkaline-carbonatite suites are: (i) prevalence of intrusive forms; (ii) abundance of cumulate assemblages (minor dunites, frequent clinopyroxenites and members of the ijolite series) and (iii) abundance of evolved rock-types. Many data demonstrate that crystal fractionation was the main process responsible for magma evolution of all Brazilian alkaline rocks. A hypothesis is proposed for the genesis of carbonatite liquids by immiscibility processes. The incidence of REE and trace elements for different major groups of lithotypes, belonging both to carbonatite-bearing and carbonatite-free districts, are documented. Sr and preliminary Nd isotopic data are indicative of a mantle origin for the least evolved magmas of all the studied occurrences. Mantle source material and melting models for the generation of the Brazilian alkaline magma types are also discussed.

Rift-related Cenozoic alkaline mafic lavas from northern Victoria Land (Antarctica) carry abundant mantle xenoliths whose oxygen fugacities (fO2) were determined to assess how the metasomatism, related to Cenozoic magmatism, affected the state of oxidation of the lithospheric mantle. The xenoliths used for this study are anhydrous spinel peridotites sampled in two localities, Greene Point and Baker Rocks, that show different extents of metasomatism: these are limited to incompatible element enrichments in Greene Point and to enrichments in major, minor and trace elements at Baker Rocks. The data set includes a composite xenolith from Baker Rocks, formed by a depleted lherzolite crosscut by an amphibole-bearing vein. Mo¨ssbauer spectroscopy was used to accurately determine the Fe3?/Fetot ratios in spinel and amphibole minerals. Amphiboles were also characterized by Single-Crystal X-ray Diffraction, and the crystallographic data were used to calculate the dehydrogenation. The oxidation state recorded by the xenoliths ranges from 0.2 to 1.5 log-bar units below the fayalite- magnetite-quartz (FMQ) buffer (DlogfO2) with the highest values observed in the metasomatized samples from Greene Point. For the vein of composite Baker Rocks xenolith, Dlog fO2 was estimated on the basis of the amphibole in -1.7 log-bar units, a value close to those calculated for all Baker Rocks xenoliths (DlogfO2 = -1.5 to -1.1 log-bar units). These results indicate a similar oxidation state for lithospheric mantle prior to the metasomatic event at Greene Point and Baker Rocks (DlogfO2 * -1.3 log-bar units). Metasomatism produced different effects in the shallow mantle at the two sites. At Greene Point, an oxidizing metasomatic melt caused the rise of fO2 in peridotite portions close to melt conduits up to FMQ. In contrast, at Baker Rocks, a metasomatizing melt with fO2 similar to that of the peridotite matrix produced chemical changes in the surrounding mantle rocks and amphibole crystallization without significantly modifying the local oxidation state. The origin of such different metasomatic melts, as well as the variety of primary magmas produced during the magmatic phase of Cenozoic rifting, is linked to the geodynamic evolution of the rift and probably involved the melting of a heterogeneous mantle source composed of a peridotite veined by pyroxene-bearing veins formed from an earlier amagmatic phase of the rift.

The separate effects of pressure (10 −4 and 1.0 GPa), water, CO 2 , oxygen fugacity and calcium doping on the liquid line of descent of a primitive leucite-basanite magma (SiO 2 = 47.06 wt%, MgO = 12.76 wt% and Mg# = 75.1) from the Montefiascone Volcanic Complex (Vulsini volcanoes, central Italy) were experimentally investigated in the 1350–1160 °C temperature range. Results indicate that low-pressure liquidus temperatures are ≤1280 °C and that the high-pressure T liquidus is 1350 °C under anhydrous conditions; the latter is lowered to ~ 1275 °C by the addition of 3 wt% water. Cr-spinel is always the liquidus phase. At comparable f O 2 values, high and low pressure runs produced the same phase assemblage (spinel + olivine + clinopyroxene) up to 50 % crystallization, although olivine was partially or totally replaced by phlogopite in hydrous experiments. An increase in oxygen fugacity and the addition of CaO determine an increase in both the degree of melt crystallization and the stability field of clinopyroxene. These determine contrasting effects on the composition of residual liquids: the former increases SiO 2 content, whereas the latter induces the desilication of melts. The replacement of olivine by phlogopite, induced by increasing amounts of water, leads to the production of glass with lower potassium contents. Comparison of the natural and experimental melts shows that many of major and trace element variations exhibited by high-K primitive ( i.e. , high Mg/Mg + Fe) magmas at Montefiascone, are consistent with their derivation from a single parental leucite-basanite melt by fractional crystallization of different proportions of mineral phases, plus carbonate assimilation. The changes in phases stability and melt composition caused by carbonate assimilation may also have fundamental implications for the origin of the calcic high-magnesium leucitites and melilitites. In particular, the complex metasomatic interactions that can develop at the interface between potassic magmas and carbonate wall rocks, may lead to melting of calcite. This low-viscosity melt readily mixes with the surrounding magma inducing the crystallization of Ca-Tschermak-rich pyroxene and hercynitic spinel, affecting significantly the SiO 2 , CaO and alumina composition of the resulting hybrid melt. A key finding of our study is that magmas such as the studied leucite-basanite may be considered parental to the wide spectrum of mafic high-K compositions in the Roman Province, which have been traditionally considered as representing near primary magmas reflecting distinct mantle source compositions and/or processes.

Artigo The alkaline-carbonatite district of Lages (Santa Catarina, Brazil), contains mafic-ultramafic and prevalent leucocratic bodies mainly composed of olivine melilitites, olivine nephelinites, basanites, phonotephrites, nepheline syenites and peralkaline phonolites. Kimberlitic pipe breccias and carbonatitic rocks are also present. Petrography, mineral and bulk-rock chemistry and mass balance calculations show that differentiated leucocratic rock-types can be derived by fractional crystallization processes from basanitic magmas. Trace element and Sr-Nd isotopic data suggest metasomatized mantle sources for the primary magmas and variable crustal contamination for the more differentiated rock-types.

The alkaline district of Fortaleza (Cearä, Brazil) consists of a number of phonotephritic plugs, domes, and dykes cropping out in the Precambrian basement, aged around 30 Ma.Chemically and petrographically the rocks range in composition from tephrites and phonolitic tephrites to peralkaline phonolites. At one locality (Caruru), olivine clinopyroxenite, essexite, and nepheline syenite xenoliths of cognate origin were also found included in phonolites. Whole rock and mineral chemistry variations coherently indicate that the various magmatic bodies of the suite essentially evolved by fractional crystallization. Mass balance calculations between bulk rocks and constituent minerals show that the evolution from tephrites to phonolitic tephrites and phonolites can be generally accounted for by subtraction of cumulates, which partly correspond to essexites and nepheline syenite xenoliths found in phonolites. Tephrites which are the least fractionated alkaline magmas in the area could, in turn, be derived from parental basanitic melts as suggested by the presence of olivine clinopyroxenite xenoliths that represent the proper fractionated solid complementary to tephritic liquids. 87