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Time-series crystallization/dissolution experiments were conducted on a natural potassic basalt seeded with bytownitic plagioclases (Plg) at atmospheric pressure, in air, at 1180- 1240 °C and isothermal dwell time up to 20 hours. Plg-seed presence promotes the early formation of new-Plg, dampening the clinopyroxene (Cpx) crystallization. New-Plgs grow at a rate from 10-6 up to 10-8 cm·s-1 as the dwell time increases. Seeds overgrow at similar rate. Cpx crystallizes with a delay of at least 3 hours; this has a significant impact on the composition of both residual melt and new-Plgs. For undercooling >35 °C the Cpx delay causes a strong supersaturation of this phase in the melt resulting in a decrease in the new-Plg nucleation rate by 2 orders of magnitude in the 3 h-experiment. In the 15h-run, Cpx coarsening and the decrease of crystallinity suggest the achievement of a near-equilibrium conditions. Cpx growth rate is in the order of 10-7 cm·s-1 showing very limited variation. Finally, for the investigated superheating (5-15 °C) only the long lasting experiments allows an estimation of Plg dissolution rate (10-9 cm·s-1) although changes in the melt composition are already detectable in the 3h-runs. As a whole our results suggest that in natural systems, the takeover of antecrysts/ xenocrysts by a magma can induce on a short time scales, changes in its initial nucleation behavior with remarkable petrological implications for the solidification paths and eruptive dynamics of potassic magmatic systems., Periodico di Mineralogia, Vol. 92 No. 1 (2023)

A review of northern Victoria Land ultramafic xenoliths, collected and studied over more than 30 years, was carried out. More than 200 samples were gathered and characterized in a coherent and comparative manner, both for mantle-derived and cumulate xenoliths. Almost 2000 analyses of major elements and more than 300 analyses of trace elements of in situ and separated olivine, pyroxenes, amphibole, spinel and glass were taken into consideration. Particular attention was devoted to mantle lithologies in order to emphasize the composition and the evolution of this portion of the subcontinental lithosphere. The three main localities in northern Victoria Land where mantle xenoliths were found (i.e. Mount Melbourne (Baker Rocks), Greene Point and Handler Ridge), over a >200 km distance, were described and compared with ultramafic xenoliths in three other localities (Harrow Peaks, Browning Pass and Mount Overlord) that are mainly cumulate in nature. Altogether, these data enabled us to reconstruct a long evolutionary history, from old depletion to most recent refertilization and metasomatic events, for this large sector of the northern Victoria Land subcontinental lithospheric mantle.

Raw materials are essential for the sustainable development of modern societies. Access to and cost-effectiveness of mineral raw materials are critical to the smooth functioning of the EU economy. The growing demand for raw materials raises increasing concerns about mineral resources. Feldspars along with quartz, the main components of granitoid rocks, are widely used in ceramic and glass industry. The need to meet the demands of the ceramic industry has stimulated research and development of new ceramic flows in granite complexes.Italy is the world’s second-largest feldspar producer (22% of total) and the world biggest importer (22% of global world trades) (European Commission). Since the strong demand is rapidly depleting the proven reserves in EU Member States, the EU ceramics sector is increasingly dependent on feldspar imports from Turkey. Thus, it is necessary to find additional sources of feldspar or to further increase inter-continental transport. At present, Buddusò-Alà dei Sardi (Sardinia-Italy) is the most important granite production area in Italy. However, granite mining activities cause serious environmental problems. Feldspar production and trade generate large amounts of pollutant and greenhouse gas emissions, due either to the energy consumption of mining activities or the transport of the finished product from the exporting countries. The areas where quarries are active suffer from landscape degradation, due to incomplete compliance or non-compliance with quarry recovery plans, considering that opening new quarries is cheaper than moving large amounts of waste. Finally, granite mining accounts for huge amounts of soil consumption, as it requires large areas in which the quarry waste accumulates.The LIFE REGS II project (LIFE19 ENV/IT/000373 LIFE REGS II) aims at demonstrating an innovative and economically-viable extraction technology to produce feldspars, of the same quality to those obtained from virgin raw material, using granite scraps. This will reduce demand for feldspar from environmentally-damaging granite mining operations as well as to minimize the soil consumption and to boost the awareness about the importance of recycling granite scraps.To this respect, samples of the granite scraps accumulated in 18 landfills located in the Buddusò-Alà dei Sardi granite quarries have been analyzed for their mineral texture and composition. Modal variability of the main mineral constituents (quartz+plagioclase±potassium-feldspar+biotite/chlorite) allowed to distinguish three main groups characterized by different ratios of feldspars/mafic phases with the exception of samples from a specific landfill that display an increase in the plagioclase at the expense of potassium-feldspar+quartz along with an increase in epidote at the expense of biotite/chlorite.Texturally potassium-feldspar occasionally occurs as microcline perthite while plagioclase is always affected by extensive alteration resulting in a variety of textural intergrowths of neoformed minerals. Such features are reflected in the inter/intra-crystalline compositional variations in terms of feldspar end-members and in the type of the alteration products. This provides the elements for a first estimate of the technological properties of felsdpars, allowing to recognize the material stored in the 18 landfills qualitatively better for commercial purpose, and to experimentally identify the most effective methods of physical treatments to enrich and extract feldspars useful for industrial uses.

This study investigates the potential use of micro-Raman spectroscopy for the quantification of water in ultrapotassic silicate glasses. A calibration was developed using experimental phono-tephritic glasses with water content ranging from ~ 1 to ~ 3 wt%. The calibration curve showed a typical direct proportionality between water content and the ratio of high- (3100–3750 cm−1) and low-wavenumber (100–1500 cm−1) spectral regions, with a linear fit coefficient m = 1.74. The comparison with the m coefficients available in literature for other silicate compositions showed a deviation of our composition as a function of some major oxides such as FeO, TiO2 and K2O, highlighting the possible influence of the polymerization degree (NBO/T: non-bridging oxygens per tetrahedron) on m coefficient. In this respect, we observed a linear relationship between m coefficient and NBO/T and a positive correlation between the area underneath the silicate region (100–1500 cm−1) and NBO/T for the phono-tephrite of this study and for other compositions spanning from basalts to phonolite and rhyolites available in literature. For ultrapotassic natural and experimental glasses characterized by the presence of CO2, documented by the carbonate peak at 1062–1092 cm−1, it has been possible to extrapolate the CO2 content by using the model of Morizet et al. (2013) obtaining values of ~ 1.1 ± 0.3 and ~ 1.7 ± 0.2 wt%, respectively. The obtained m coefficient was applied to estimate water content of natural phono-tephritic glasses belonging to the Colli Albani Volcanic District. Moreover, we estimated water content also for some natural K-foiditic glasses from the same volcanic district. Since the m coefficient results to be strongly dependent on the chemical composition of the sample of interest, the coefficient estimated for the phono-tephrites of this study could result in significant overestimation or underestimation of the water content of the Colli Albani Volcanic District K-foiditic natural samples. Thus, we extrapolated the m coefficient for the K-foiditic samples by means of an equation obtained in this study as function of the polymerization degree (NBO/T).

We present new experimental data on major and trace element partition coefficients (D) between clinopyroxene and a K-basaltic melt from Procida Island (Campi Flegrei Volcanic District, south Italy). Time-series experiments were conducted at 0.8 GPa and 1080–1250 °C aiming to investigate the role of the crystallization kinetics on trace elements partitioning behaviour at a pressure relevant for deep magmatic reservoirs. Results indicate that large ion lithophile elements (LILE) are incompatible (e.g., DSr ≤ 0.15), light rare elements (LREE; e.g., DLa ≤ 0.20) are always more incompatible than heavy rare elements (HREE), which in some cases result to be compatible with clinopyroxene (e.g., DDy = 1.40); high field strength elements (HFSE) are generally incompatible (DHFSE ≤ 0.8), while transition elements (TE) range from slightly incompatible (e.g., DV = 0.6) to highly compatible (e.g., DCr = 63). The calculated D values for LILEs, REEs, HFSEs, and TEs tend to decrease with the increase of temperature and to increase with increasing tetrahedrally-coordinated aluminium content, in agreement with the previous studies. Moreover, we observed the influence of the growth rate on the partition coefficients, with the highest DREE values calculated in the runs with the highest growth rate (~10−7 cm s−1), due to the less efficient rejection of incompatible elements during rapid crystal growth, that in this study is not linked to disequilibrium conditions, but to the presence of pre-existing nuclei. Additionally, the apparent increase in DREE values with time observed in some runs is not referable to a change in time but rather to the different degrees of polymerization, expressed as the ratios NBO/T of these melts, strictly related to a loss of Fe occurred during the experiments, and thus to a different melt viscosity. Finally, the application of the experimental clinopyroxene-melt partition coefficients highlights that the deepest step of the magmatic differentiation in the Campi Flegrei Volcanic District is represented by the fractionation of about 20–30% of a clinopyroxenitic mineral assemblage from a basaltic parental magma.

Deep geothermal contributions can affect the thermal equilibrium of glacial systems, which can induce changes in their thermal state. These changes can be influenced by glacier dynamics and by the different ice flow velocities experienced over time, which dictate the static and dynamic interactions with glacial trough bedrock. To assess such interactions and to weight the effects of ice mass thermalisations on bedrock, 2D multistage numerical modelling was performed for Priestley Glacier (an outlet glacier) in the East Antarctic glacial system (northern Victoria Land), which has experienced extreme heat flux variations related to rifting and late Cenozoic volcanism. The thermal evolution of Priestley Glacier over the last ~500 ka was modelled considering the mutual contributions of local and deep thermal sources through a parametric variation in the geothermal heat flux. The ice mass velocity was indirectly taken into account by assuming an ice persistence time over the bedrock under timelled considering the mutual contributions of local and deep thermal sources through a parametric variation in the geothermal heat flux. The ice mass velocity was indirectly taken into account by assuming an ice persistence time over the bedrock under time-dependent modelling conditions. Ice thickness and geothermal heat fluxes, varying from 50 to 120 mW/m2, were conditions are strongly linked in determining the thermal state of the glacier base and consequently its impact on basal erosion. According to the adopted ice stationing levels, heat flux conditions not exceeding 70 mW/m2 are needed for preserving a dry-based glacier only assuming velocity conditions equal to or lower than those observed to date along Priestley Glacier. Assuming increased velocity conditions, the glacier sensitivity to heat fluxes decreases, and high to very high heat fluxes are not sufficient to cause glacier base transitions to wet states.

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 (

Isotopic disequilibrium is increasingly recognized as a common feature of magmatic systems, but the details of the mechanism(s) underpinning the development of isotopic disequilibrium during partial melting processes are not fully understood. Partial melting of mica-rich lithologies may be predicted to generate melts enriched in radiogenic Sr compared to the bulk protolith compositions due to the typically high Rb/Sr ratio coupled with low melting temperature of mica in crustal rocks. Here we report a puzzling case study where the Sr-isotope composition of the melt fraction (leucosome) of partially molten metapelites (migmatites) is less radiogenic than the restitic component (melanosome). The examined migmatites fringe (50m wide zone) a low-pressure (≤200 MPa), high-temperature (1050°C) quartz-dioritic intrusion, which was emplaced in the Gennargentu Igneous Complex (Sardinia, Italy) at 306626Ma (bulk-rock Rb/Sr dating). The migmatites derive from anatexis of the muscovite-rich metapelitic wall-rocks. They include a quartzo-feldspathic leucosome and a melanosome containing cordierite, K-feldspar, plagioclase, biotite, Fe-Ti oxide minerals and both corundum and hercynite. The leucosome has a less radiogenic Sr and more radiogenic Nd isotope composition than the melanosome (87Sr/86Sr (306 Ma) = 0·71068 and 0·71536; εNd(306Ma) = -6·4 and -9·2, respectively), with bulk migmatite samples having intermediate compositions. The significantly lower content of mica in the migmatites compared to the protolith indicates that muscovite and, to a lesser extent, biotite largely contributed to melt formation. However, the leucosome volume (50%) estimated through mass balance calculations is considerably higher than the amount of melt (≤10 vol. %) generally produced by mica-dehydration melting in the crust, suggesting that partial melting was enhanced by an external hydrous fluid. The O-isotope composition of the migmatites is lower than the typical metapelite values (>10‰) but overlaps with the δ18O range of the quartz-diorites (8·8-9·9‰), suggesting that such a hydrous fluid was released from the quartz-dioritic intrusion. We put forward a model whereby the anatexis temperature conditions (T < 800°C) favored the preservation of isotopic disequilibrium of micas and plagioclase in the protolith. In this context, the leucosome formed by the preferential melting of less radiogenic plagioclase rather than more radiogenic micas. The melt was then efficiently separated from the melanosome containing restitic biotite and 'peritectic K-feldspar and magnetite' derived from mica breakdown. During the anatectic process the quartz-diorite provided not only the heat budget, but also the fluid amount responsible for (i) the hydration of the pelitic country rock, (ii) the increase of melt fraction, and (iii) the higher mobility of anatectic magma.

Dissolution of clinopyroxene (cpx) in a K-basaltic melt from the Campi Flegrei Volcanic District (Italy) has been investigated through dissolution and dissolution-crystallization experiments at pressure of 0.8 GPa, superliquidus temperature of 1350 °C, and dwell times between 0.5 and 1 h. The obtained dissolution rates range from 7.9·10−6 cm s−1 to 6.1·10−6 cm s−1 as a function of dwell time. In the dissolution-crystallization experiment (1300 °C; 0.8 GPa; 2 h), the formation of overgrowth rims accompanied by new cpx crystals suggests that the injection of recharge magmas in basaltic reservoir may lead to inverse or oscillatory zonation. The interaction between cpx and K-basaltic melt at ~1570 °C was studied by in situ radiography using synchrotron radiation combined with the Paris-Edinburgh press. This resulted in cpx resorption to occur depending on the temperature conditions with respect to the liquidus temperature of the cpx (TcpxL). The calculated cpx dissolution rates are ~5·10−3 cm s−1 at T ≤ TcpxL and ~ 3·10−2 cm s−1 at T ≥ TcpxL. The role of crystal dissolution in the estimation of magma residence times has been also tested for a natural magmatic system by interpolating the dissolution rates (~10−5–10−6 cm s−1) with the textural data of cpx phenocrysts from the Agnano-Monte Spina pyroclastic deposit at Campi Flegrei caldera (Campanian region, Italy). Results from calculations indicate that the time required for partial or complete resorption of phenocrysts varies from ~0.5 to ~40 h, and that the effect of crystal dissolution may be relevant to estimate magma residence times whether significant dissolution occurs during magma mixing processes.

Aiming to improve the current knowledge about amphibole growth kinetics at deep crustal levels, new amphibole growth rate data are provided. Our findings, indeed, may be useful to correctly interpret the textural features of amphibole-bearing mafic cumulates and rocks, and for a better constraining of the timescales of magmatic processes at upper mantle-lower crustal depths. Experiments were performed to determine the amphibole growth rates in a primitive alkaline basalt from Procida island (Campi Flegrei Volcanic District, southern Italy) at the following conditions: temperature of 1030 and 1080 °C, pressure of 0.8 GPa, water content in the range 3.3-4.2 wt%, and variable dwell time from 0.25 to 9 h. Amphibole growth rates range from 1.5·10-7 to 2.9·10-8 cm·s-1 with increasing the duration of the experiments. It is observed that, keeping a constant dwell time, an increase of the experimental temperature or of the water content results in comparable growth rate increase. Coexisting synthetic amphibole and clinopyroxene show a faster growth rates in favour of amphibole regardless of the dwell time, since the chemical and structural similarities of these minerals cause kinetic competition. Moreover, the chemical composition of amphibole is influenced mainly by the experimental time; in detail, in the shortest (≤3 h) and low temperature runs edenite is the prevailing composition whereas the magnesiohastingsitic term becomes dominant at higher temperature and longer run duration. Based on the interpretation of the Fe-Mg exchange coefficient values between amphibole and coexisting liquid, the magnesiohastingsitic amphibole is considered to be the stable term at the investigated run conditions. Finally, the resulting growth rates have been applied to constrain the crystallization time of natural amphiboles and clinopyroxenes from the Oligo-Miocene cumulates of north-western Sardinia (i.e., Capo Marargiu Volcanic District, Italy), yielding crystallization times in the range 1.46-3.12 yr.

Clinopyroxene growth rates were experimentally determined in a K-basaltic rock from Campi Flegrei Volcanic District (south Italy). The primary objective was to provide constraints on the clinopyroxene crystallization kinetics at high pressure: we carried out a series of experiments at 0.8 GPa, 1030–1250 °C, 1 ≤ H2O ≤ 4 wt.%, with durations of 0.25, 3, 6 and 9 h. Overall, growth rate reaches a maximum value in the shortest experiments (~ 3·10−7 cm·s−1), decreasing to ~ 1·10−8 cm·s−1 in the longest duration runs. Temperature and water content do not seem to significantly affect the growth rate. Moreover, partition coefficients based on the crystal-liquid exchange show that mineral chemistry progressively approaches equilibrium with increasing run duration. Furthermore, to estimate the magma recharge of the deep reservoirs, we combined the determined growth rates with data from thermobarometry and from crystal size distribution analyses of clinopyroxenes in the most primitive scoria clasts of the Campi Flegrei Volcanic District (CFVD). We obtained a minimum residence time of ~ 5 months for the larger clinopyroxene population, and an ascent velocity of ~ 0.5·10−4 m·s−1 for the CFVD K-basaltic magma. The smaller clinopyroxene phenocrysts and microlite populations, however, suggest that the late stage of Procida magma crystallization took place in disequilibrium conditions.

Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O < 1 and high CO2 activity in the melt, as testified by the CO3 in the clinopyroxene melt inclusions, by the early crystallization of CO3-bearing apatite and by the high CO2 activity in the free volatile phase that led to crystallization of calcium carbonate in the scoria clast vesicles. The K-foiditic magmas plot on the Cpx + Lc + melt divariant surface of the Ol-Cpx-Lc-Mel-H2O-CO2, P ≥ 0.2 GPa and T ≤ 1100 °C. The assimilation of cold carbonate by hot magmas is an important open-system process allowing the establishment of aH20 < 1 condition in the volatile-rich, Colli Albani magma chambers where the stability fields of the olivine and phlogopite are reduced in favor of clinopyroxene and leucite. Trace element modelling indicates large amount of carbonate assimilation (~12.4 wt%) involved in the differentiation process that origins the K-foiditic magmas starting from a K-rich, phonotephritic parental magma. The large amount of assimilate carbonate is consistent with the peculiar distribution of the latent heat across the crystallization interval of the phonotephritic parental magma. The isenthalpic assimilation process is very efficient in the phonotephritic magma because the crystallization of clinopyroxene and leucite in equilibrium with a K-foiditic melt proceeds over a relatively large temperature interval (>200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.

The alkaline basaltic magmas at Mt. Overlord (northern Victoria Land, Antarctica) entrained abundant ultramafic xenoliths (wehrlites, clinopyroxenites and hornblendites). Textures, bulk rock compositions, mineral chemistry and thermobarometric calculations indicate that the xenoliths represent cumulates that crystallised at the mantle–crust boundary. In particular, the major and trace element compositions of the bulk rocks and minerals indicate that the Mt. Overlord cumulates were formed through processes of crystal fractionation that affected hydrous basanitic magmas. Some of the xenoliths have textural features that suggest a lengthy (> 13 Myr) post-emplacement history at relatively low temperatures (1050–1100 °C) and high pressures (0.8 to 1.4 GPa) and that their primary parental melts were therefore related to the earliest phases of Cenozoic magmatism. These processes produced a “wet and hot deep zone” that had a strong influence on the thermochemical evolution of the lower crust beneath Mt. Overlord.

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.

The recent geological history of Ischia Island is characterized by slope-scale gravitational deformations closely related to volcano-tectonic dynamics of the Mt. Epomeo resurgent caldera. This study focuses on the gravitational deformation that involves alkali-trachytic lava and trachytic ignimbrite flow-units of Mt. Nuovo, located in the western portion of Mt. Epomeo. A preliminary, high-resolution engineering-geological model was obtained through geological, geomorphological and geophysical surveys and reveals a complex morpho-structure with geomorphological evidence of gravitational instability. The complexity of the ongoing slope deformations is confirmed by field geo-structural evidences that led to the identification of a multiple compound mechanism with a main rupture surface which is about 200 m deep. This geometry was better constrained by passive seismic investigations consisting in noise measurements, focused on resonance frequencies of the soil (i.e. based on H/V Nakamura approach). In addition, a close relationship between the outcrop of Mt. Epomeo Green Tuff breccia layers and the distribution of hydrothermal emissions and gas vent can be inferred, as it is related to the higher permeability of the breccia layers with respect to the main Mt. Epomeo Green Tuff flow unit, where the ascent path of deep hydrothermal fluids developed along faults and fracture networks. © Società Geologica Italiana, Roma 2015.

Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from mantle depths. On this basis, we have performed hydrous crystallization experiments for a quantitative understanding of the role of H2O in the differentiation of deep-seated trachybasaltic magmas at the key pressure of the Moho transition zone. For H2O = 2.1&ndash, 3.2 wt %, the original trachybasaltic composition shifts towards phonotephritic magmas never erupted during the entire volcanic activity of Mt. Etna. Conversely, for H2O = 3.8&ndash, 8.2 wt %, the obtained trachybasalts and basaltic trachyandesites reproduce most of the pre-historic and historic eruptions. The comparison with previous low pressure experimental data and natural compositions from Mt. Etna provides explanation for (1) the abundant release of H2O throughout the plumbing system of the volcano during impulsive ascent of deep-seated magmas, (2) the upward acceleration of magmas feeding gas-dominated, sustained explosive eruptions, (3) the physicochemical changes of gas-fluxed magmas ponding at shallow crustal levels, and (4) the huge gas emissions measured at the summit craters and flank vents which result in a persistent volcanic gas plume.

The Zannone Hydrothermal Field (ZHF, 60 km2), located in the shallow-waters (3.0 Ra), similar to those recorded in other shallow water areas of the Tyrrhenian Sea (Stromboli and Panarea islands). Geochemical analyses suggest that the vented hydrothermal volatiles are probably associated with residual magma batches, chemically similar to the Pleistocene trachytes cropping out at Ponza Island, that still provide thermal energy to the submarine geothermal system. The vent activity at the ZHF seems to be controlled by the tectonic structures of the Ponza-Zannone structural high and fed by hot volatiles of magmatic origin. At present it is characterized by slow and diffuse degassing but in recent times it encompassed more explosive events. Finally, diffuse episodes of such activity have to be considered in terms of possible triggering mechanisms of shallow instability phenomena.

Amphibole growth rates were experimentally determined at hydrous (3.3–4.2 wt% H2O), isobaric (0.8 GPa) conditions, variable temperature (1030 and 1080 °C) and dwell time (0.25, 3, 6, and 9 h), using as starting material a primitive alkaline basalt from Procida island (Campi Flegrei Volcanic District, south Italy). Amphibole growth rates decrease from 1.5·10−7 to 2.9·10−8 cm s−1 as the duration of the experiments increase from 0.25 to 9 h. Moreover, increasing both temperature and water content leads to similar growth rate increase at constant dwell time. The comparison between amphibole and clinopyroxene growth rates determined at the same experimental conditions reveals for amphibole a faster growth relatively to the coexisting clinopyroxene, regardless of the dwell time. Furthermore, the experimental time appears to be a critical parameter for the composition of synthetic amphiboles; specifically, edenite is the dominant composition in short experiments (≤3 h), particularly, at low temperature (1030 °C), whereas the magnesiohastingsitic amphibole becomes progressively more important shifting towards longer duration and higher temperature run conditions. The magnesiohastingsite, on the basis of the amphibole-liquid Fe-Mg exchange coefficient values, results to be the compositional term representative of amphibole-melt equilibrium at the investigated P-T-H2O conditions. Finally, experimental growth rates from this study have been used to investigate the crystallization time of natural amphiboles and clinopyroxenes from the Oligo-Miocene cumulates of north-western Sardinia (i.e. Capo Marargiu Volcanic District, Italy), yielding crystallization times of 1.46–3.12 yr.

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.

Among the abundant mantle xenoliths carried by the Cenozoic alkaline basalts of northern Victoria Land, Antarctica, we have studied a suite of clinopyroxene-rich cumulates collected at Browning Pass (Mt. Melbourne Volcanic Province), ranging in composition from wehrlites to clinopyroxenites. Clinopyroxenes belonging to both the Cr-diopside (wehrlites) and Al-augite series (ol-clinopyroxenites and clinopyroxenites) all show convex-upward REE patterns. Modal and cryptic metasomatism has variably affected the xenoliths, accounting for amphibole replacement of clinopyroxene and/or selective enrichment in incompatible elements. Chemical features, along with O-Sr-Nd isotopic data, indicate that both the parental magmas and the metasomatizing melts are related to the Cenozoic magmatic activity and imply the role of at least two mantle components with distinct isotopic fingerprints. The positive covariation between ?18Oolivine and the amount of modal olivine, and between ?18Oolivine and olivine Fo content, suggest that during the fractionation of olivine and pyroxene, the parent magma experienced a change in O-isotope composition; a low-?18O melt component was not only added to the minerals during the metasomatic event but was also involved in the genesis of the parental melts. The Browning Pass cumulates are used to constrain the origin of the Antarctic Cenozoic magmatism from a heterogeneous mantle source whose depleted end-member is inferred to be the local lithospheric mantle, whereas the enriched end-member is represented by early metasomatic veins or domains emplaced into the depleted mantle during an amagmatic phase of rifting at the beginning of Ross Sea opening. Thermobarometric analysis of the process shows that the respective contribution to magma generation of the two end-members is related to the change of local thermal regime induced by an 'edge effect' in the mantle circulation at the lithospheric step between the thick East Antarctic craton and the thinned Ross Sea crust.

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.

We have refined the clinopyroxene-based hygrometer published by Armienti et al. (2013) for a better quantitative understanding of the role of H2O in the differentiation of Etnean magmas. The original calibration data set has been significantly improved by including several experimental clinopyroxene compositions that closely reproduce those found in natural Etnean products. To verify the accuracy of the model, some randomly selected experimental clinopyroxene compositions external to the calibration data set have been used as test data. Through a statistic algorithm based on the Mallows’ CP criterion, we also check that all model parameters do not cause data overfitting, or systematic error. The application of the refined hygrometer to the Mt. Etna 2011–2013 lava fountains indicates that most of the decreases in H2O content occur at P < 100 MPa, in agreement with melt inclusion data suggesting abundant H2O degassing at shallow crustal levels during magma ascent in the conduit and eruption to the surface.

During the 2001 eruption of Mount Etna, two independent vent systems simultaneously erupted two different lavas. The Upper Vents system (UV), opened between 3100 and 2650 m a.s.l., emitted products that are markedly porphyritic and rich in plagioclase, while the Lower Vents system (LV), opened at 2100 and 2550 m a.s.l., emitted products that are sparsely porphyritic with scarce plagioclase. In this study, the crystal size distributions (CSDs) of plagioclase were measured for a series of 14 samples collected from all the main flows of the 2001 eruption. The coefficient of R 2 determination was used to evaluate the goodness of fit of linear models to the CSDs, and the results are represented as a grid of R 2 values by using a numerical code developed ad hoc. R 2 diagrams suggest that the 2001 products can be separated into two main groups with slightly different characteristics: plagioclase CSDs from the UVs can be modeled by three straight lines with different slopes while the plagioclase CSDs from the LVs are largely concave. We have interpreted the CSDs of the UVs as representing three different populations of plagioclases: (i) the large phenocrysts (type I), which started to crystallize at lower cooling rate in a deep reservoir from 13 to 8 months before eruption onset; (ii) the phenocrysts (type II), which crystallized largely during continuous degassing in a shallow reservoir; and (iii) the microlites, which crystallized during magma ascent immediately prior to the eruption. The plagioclase CSD curves for the LVs lava are interpreted to reflect strong and rapid changes in undercooling induced by strong and sudden degassing.

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.

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.

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.

Peridotite xenoliths found in Cenozoic alkali basalts of northern Victoria Land, Antarctica, vary from fertile spinel-lherzolite to harzburgite. They often contain glass-bearing pockets formed after primary pyroxenes and spinel. Few samples are composite and consist of depleted spinel lherzolite crosscut by amphibole veins and/or lherzolite in contact with poikilitic wehrlite. Peridotite xenoliths are characterized by negative Al2O3–Mg# and TiO2–Mg# covariations of clino- and orthopyroxenes, low to intermediate HREE concentrations in clinopyroxene, negative Cr–Al trend in spinel, suggesting variable degrees of partial melting. Metasomatic overprint is evidenced by trace element enrichment in clinopyroxene and sporadic increase of Ti–Fetot. Preferential Nb, Zr, Sr enrichments in clinopyroxene associated with high Ti–Fetot contents constrain the metasomatic agent to be an alkaline basic melt. In composite xenoliths, clinopyroxene REE contents increase next to the veins suggesting metasomatic diffusion of incompatible element. Oxygen isotope data indicate disequilibrium conditions among clinopyroxene, olivine and orthopyroxene. The highest delta18O values are observed in minerals of the amphibole-bearing xenolith. The delta18Ocpx correlations with clinopyroxene modal abundance and geochemical parameters (e.g. Mg# and Cr#) suggest a possible influence of partial melting on oxygen isotope composition. Thermobarometric estimates define a geotherm of 80°C/GPa for the refractory lithosphere of NVL, in a pressure range between 1 and 2.5 GPa. Clinopyroxene microlites of melt pockets provide P–T data close to the anhydrous peridotite solidus and confirm that they originated from heating and decompression during transport in the host magma. All these geothermometric data constrain the mantle potential temperature to values of 1250–1350°C, consistent with the occurrence of mantle decompressional melting in a transtensive tectonic regime for the Ross Sea region.