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The Campi Flegrei geothermal system sets in one of the most famous and hazardous volcanic caldera in the world. The geothermal dynamics is suspected to have a crucial role in the monitored unrest phases and in the eruption triggering as well. Numerical models in the literature do not properly consider the geochemical effects of fluid-rock interaction into the hydrothermal circulation and this gap limits the wholly understanding of the dynamics. This paper focuses on fluid-rock interaction effects at the Campi Flegrei and presents relevant information requested for reactive transport simulations. In particular, we provide: (1) an extensive review of available data and new petrographic analyses of the San Vito cores rearranged in a conceptual model useful to define representative geochemical and petrophysical parameters of rock formations suitable for numerical simulations and (2) the implemented thermodynamic and kinetic data set calibrated for the San Vito 1 well area, central in the geothermal reservoir. A preliminary 0D-geochemical model, performed with a different contribution of CO2 at high (165 °C) and low (85 °C) temperatures, firstly allows reproducing the hydrothermal reactions over time of the Campanian Ignimbrite formation, the most important deposits in the case study area.

Fluorine-, boron-, and magnesium-rich metamorphosed xenoliths occur in the Campanian Ignimbrite (CI) deposits at Fiano (southern Italy), at about 50 km northeast of the sourced volcanic area. These rocks originated from Mesozoic limestones of the Campanian Apennines, embedded in a fluid flow. The studied Fiano xenoliths consist of ten fluorophlogopite-bearing calc-silicate rocks and five carbonate xenoliths, characterized by combining mineralogical analyses with whole rock and stable isotope data. The micaceous xenoliths are composed of abundant idiomorphic fluorophlogopite, widespread fluorite, F-rich chondrodite, fluoborite, diopside, Fe(Mg)-oxides, calcite, humite, K-bearing fluoro-richterite and grossular. Out of the five mica-free xenoliths, two are calcite marbles, containing very subordinate fluorite and hematite, and three are weakly meamorphism carbonates, composed of calcite only. The crystal structure and chemical composition of fluorophlogopite approach those of the end member. The Fiano xenoliths are enriched in trace elements with respect to the primary limestones. Comparison between the REE patterns of the Fiano xenoliths and those of both CI and Somma-Vesuvius marble and carbonate xenoliths shows that the Fiano pattern on the whole both overlaps that of Somma-Vesuvius marble and carbonate xenoliths, and yet reproduces the trend of CI rocks. δ13C and δ18O values depict the same trend of depletion in the heavy isotopes observed in the Somma-Vesuvius nodules, related tothermometamorphism. Trace element distribution, paragenesis, stable isotope geochemistry and data modelling point to infiltration of steam enriched in F, B, Mg, As into carbonate rocks at temperature of ca. 300-450°C during the emplacement of the CI.

A lithoid tuff, found in 2011 (Ricci pit, Agro Pontino, Southern Lazio, Italy), was studied for its composition, origin and palaeogeographical implications. This tuff was the first occurrence of a Würmian-age tephra layer, encountered in the coastal basins of Southern Lazio. Based on its mineralogy and isotopic composition (Sr and Nd), its stratigraphic position and the pre- and post-depositional soil formation and weathering, it was identified as a distal tephra deposit from the Colli Albani volcano, connected with the Albano 5-7 eruptive stage and dating from 40-36 ka BP. The lithoid tuff consists of tephra that were slightly reworked and subsequently lithified, when this central part of the Agro Pontino graben still consisted of a non-dissected, level lagoonal plain. The study confirms the earlier established importance of this tephra layer as stratigraphic marker for Central Italy, and shows that its distribution is wider than earlier assumed, notably to the SE of the Colli Albani volcano.

The medicinal properties of mineral pigments, mordants or washing powders presented in Pliny’s 35th book of Natural History and in those of other authors of the Greco-Roman world (Galen, Dioscorides, Scribonius) have been relatively little researched compared to their botanical counterparts. Over the last fifteen years there has been detailed geoarchaeological prospections and chemical/mineralogical analyses allowed to identify some of these minerals in their recorded places, essentially of origin largely on volcanic islands in the Aegean (Photos-Jones & Hall, 2011). The medicinal minerals of antiquity are now understood to consist primarily of layered silicates, sulphates and metal oxides/sulphides (Photos-Jones et al., 2015). Recent studies have been also focused on (1) processing methods by which raw materials could have been converted to finished products, i.e. the medicinals, and (2) assaying for purity (Hall and Photos-Jones 2005; 2009; Photos-Jones and Hall 2010). Moreover microbiological work on layered silicates from some volcanic islands in the Aegean (Samos) and stamped archaeological earths (terra sigillata) (Lemnos) has shown them to be antibacterial (Photos-Jones et al., 2015). The present research focuses on the second group of medicinal minerals, namely sulphur and sulphates and in particular solfataric alum efflorescences from two volcanic landscapes, in Greece and Italy, i.e. Melos (Western Cyclades) and Campi Flegrei (Naples), respectively. Both regions are known to have been exploited in antiquity and later periods. The chemistry and mineralogy of a small number of geological samples collected from each are examinated. For Melos, some samples have undergone field-based heating and processing while other samples have been used in microbiological testing. The results suggest that solfataric alum consists primarily of the minerals alunogen and K-alum with strong antibacterial (but not antifungal) properties. It is suggested that Greco-Roman medicinal minerals are likely to reflect long established geophagic practices incorporated within medical prescriptions, the antiquity of which may predate, by far, the historical periods. In addition, given that currently 'extreme' landscapes are the focus for the discovery of new drugs, an understanding of the nature and properties of the Greco-Roman medicinal minerals deriving from volcanic landscapes might be relevant to both antiquity and today. Photos-Jones E. & Hall A.J. 2010. Stypteria phorime as alunogen in solution: possible pointer to the gradual cooling of the Melos geothermal system. Hellenic J. Geosci., 45, 217-226. Photos-Jones E. & Hall A.J. 2011. Lemnian Earth and the earths of the Aegean. Glasgow, Potingair Press. Photos-Jones E., Keane C., Jones A.X., Stamatakis M., Robertson P., Hall A.J. & Leanord A. 2015. Testing Dioscorides' medicinal clays for their antibacterial properties: the case of Samian Earth. J. Archaeol. Sci., 57, 257-267.

The Campi Flegrei caldera is one of the highest-risk volcanic areas on the Earth and the drilling exploiting activities carried by the Azienda Geologica Italiana Petroli (AGIP) and the Società Anonima Forze Endogene Napoletane (SAFEN) since the '40 have produced the main constrains to the definition of the subsurface structure of the caldera. The eastern part of the caldera represents among the least known in the area in terms of both volcanic and geothermal evolution. Recently, in the 2012, the Campi Flegrei Deep Drilling Project (CFDDP) allowed performing a 506m hole in this sector of the caldera, i.e. in the Bagnoli Plain, where the western districts of the Neapolitan city developed. Here, we present the preliminary results from mineralogical, geochemical and petrological investigations of drilling core samples collected at -443 m and -506 m of depths. Scanning electron microscopy (SEM), microanalysis by energy dispersive spectroscopy (EDS) together with investigations by back-scattered electron mode (SEM-BSE), and powder X-Ray diffraction (XRD) allowed: 1) defining the primary sample lithology; 2) examining the features of both primary and secondary minerals; 3) describing the relationships among texture and secondary mineralization. Sr isotope analyses were furthermore performed on separated feldspars. Density measurements were also carried out on the bottom core. The investigated samples are representative of strongly altered, massive pyroclastic tuffs, which made of a chaotic ashy to sandy matrix including low crystalline juvenile scoria and pumice fragments. Textural features of secondary mineralization are consistent with circulation of hydrothermal fluids as the results of a wide geothermal resource in the caldera. Comparing the paleo-temperature inferred by authigenic minerals occurrence and the temperature measured at the bottom hole (~60°C) during geophysical logs, we suggest the cooling of the hydrothermal system in the eastern sector of the caldera.

Fluorine-rich metamorphosed xenoliths associated to the distal Campanian Ignimbrite (CI) tephra (Campania region, southern Italy) have long attracted the interest of the mineralogical community (i.e. Scacchi, 1890; Zambonini, 1919; Masi & Turi, 1972; Balassone et al., 2002). These rocks derive from the Mesozoic carbonate lithotypes of the Campanian Apennine, embedded in the pyroclastic flow and presently resting at the bottom of the tuff formations. The sedimentary protoliths suffered from the action of hot, volatile-rich pyroclastic flow, and consequently were affected by thermal metamorphism to various degrees. Their peculiarity is the occurrence of F- and Mg-bearing phases, with an ubiquitous presence of neoformed fluorite. The occurrence at Fiano quarries (the so-called “Tufare”) is the classical locality for these rock xenoliths. Similar rocks were also found in the CI of the Caserta area, and in the Latium region (Colli Albani). This research aims both at a crystal chemical study of fluorophlogopite occurring in the Fiano xenoliths, and at a geochemical and volcanological survey, to constrain the petrogenesis processes related to this rare F-, Mg-rich assemblage and to CI. The analysed samples belong to two lithotypes: mica-bearing clasts and variably metamorphosed carbonate blocks. The former lithotype is represented by abundant fluorite, followed by fluorophogopite, F-rich chondrodite, fluoborite, diopside and (Fe,Mg)-oxides. Minor to trace contents of calcite, humite, tremolite, and grossular also occur. Carbonate rocks can show calcite only, or also trace amounts of fluorite. The Fiano micas composition approaches that of the Vesuvius micas from the 1872 eruption (Balassone et al., 2013). The micas belong to the 1M polytype and have crystal chemical features typical of fluorophlogopites i.e., low c lattice parameter (~ 10.13 Å), (~ 2.060 Å) and (~ 3.135 Å) distances. New data on minor to ultratrace elements amounts found in the studied clasts, together with Carbon and Oxygen isotope data will be reported and interpreted in a petrogenetic and volcanological frame. Balassone G., Franco E., Mattia C.A., Petti C. & Puliti R. 2002. Re-examination of fluosiderite, an unknown mineral from southern Italy: equal to fluorine-rich chondrodite. Eur. J. Min., 14, 151-155. Balassone G., Scordari F., Lacalamita M., Schingaro E., Mormone A., Piochi M., Petti C. & Mondillo N. 2013. Trioctahedral micas in xenolithic ejecta from recent volcanism of the Somma-Vesuvius (Italy): crystal chemistry and genetic inferences. Lithos, 160-161, 84-97. Masi U. & Turi B. 1972. Frazionamento isotopico del carbonio e dell'ossigeno negli inclusi calcarei metamorfosati del "Tufo grigio campano" Auct. di Fiano (Salerno). Per. Min., 41, 291-310. Scacchi A. 1890. La regione vulcanica fluorifera della Campania. Mem. R. Com. Geol. It., I, 1-48. Zambonini F. 1919. Il tufo pipernoide della Campania e i suoi minerali. Mem. Descr. Carta Geol. It., 7, 130 pp.

In this paper we describe recent applications of micro-infrared imaging in the Earth sciences. We address, in particular, the use of Fourier-transform infrared (FTIR) spectroscopy in characterizing the zoning and speciation of H and C in a variety of geological materials, including microporous minerals, nominally anhydrous volcanic minerals (NAMs), and crystal inclusions. These investigations show that use of the modern techniques of FTIR imaging enables detection of the zoning of volatile species across the studied samples, and possible configuration changes of structurally-bound carbon molecular species (e. g., CO(2) vs CO(3)) during crystal growth. Such features, which are not accessible with other micro-analytical techniques, may provide information about the physicochemical properties which act as constraints in the genesis of the samples, and important information about the evolution of the geological system. Tests performed with focal-plane-array detectors (FPA) show that resolution close to the diffraction limit can be achieved if the amounts of the target molecules in the sample are substantially different. We also point out the possibility of using FTIR imaging for investigations under non-ambient conditions.

Melt inclusions (MIs) are micrometric-sized and variable-shaped impurity parcels of glass vesicles solids present within cavities or fractures of crystals. Because representing melt droplets that were trapped during crystal growth, they are believed to record the variable physico-chemical conditions of the hosting multi-phase system. Therefore, MIs are unique probe of near-liquidus magmatic conditions, otherwise inaccessible to Earth Scientists, and are widely used to integrate and corroborate conventional petrological and volcanological techniques based on mineral phases and whole rocks. Electron microprobe (EMP-WDS) and microscopy (SEM-EDS), and Fourier Transform Infra Red (FT-IR) spectroscopy are well-established analytical techniques, commonly used to determine composition of the magma from which MIs formed. Noteworthy, FT-IR is usually adopted to determine the content of dissolved H2O and CO2, providing i) essential information for entrapment pressures, hence depths of crystal growth, and ii) constraints to the volatile budget of magmas. Assessing such volatile contents has significant implications for the understanding of magma evolution and migration, from the depths of parental magma genesis, through the main depths of crustal storage, up to surface. The MI-based quantification of volatile contents and the recognition of degassing patterns are also vital for deciphering magma rheology, which largely affects eruptive dynamics and style. Limits to melt inclusion studies are i) their typically very small size (< 100 m), ii) the possible late and secondary crystallization, iii) the diffusivity-driven chemical exchange between melt and host crystal, iv) and the alteration phenomena that mask or even delete the original melt composition. Here, we present a study of glass/melt inclusions in phenocrysts from Procida Island (Phlegraean Volcanic District, South Italy), analyzed for combined SEM-EDS electron microscopy, EMP-WDS microchemistry and FT-IR spectroscopy. In particular, we have characterized the distribution of volatile H and C species across both the host crystals and the inclusions, by using a focal-plane-array (FPA) of detectors. The FPA technique allows the acquisition of a large number of IR spectra simultaneously and generate mid-IR images with high resolving power of the target molecules in the H-O-C system. The integration of these analytical techniques is a mandatory step in order to provide definite advances in MI characterization and data interpretation

In this paper we describe recent applications of micro-infrared imaging in the Earth sciences. We address, in particular, the use of Fourier-transform infrared (FTIR) spectroscopy in characterizing the zoning and speciation of H and C in a variety of geological materials, including microporous minerals, nominally anhydrous volcanic minerals (NAMs), and crystal inclusions. These investigations show that use of the modern techniques of FTIR imaging enables detection of the zoning of volatile species across the studied samples, and possible configuration changes of structurally-bound carbon molecular species (e.g., CO2 vs CO3) during crystal growth. Such features, which are not accessible with other micro-analytical techniques, may provide information about the physicochemical properties which act as constraints in the genesis of the samples, and important information about the evolution of the geological system. Tests performed with focal-plane-array detectors (FPA) show that resolution close to the diffraction limit can be achieved if the amounts of the target molecules in the sample are substantially different. We also point out the possibility of using FTIR imaging for investigations under non-ambient conditions.

Melt inclusions (MIs) represent pristine melt droplets trapped in early forming phenocrysts, which record the variable physico-chemical conditions of their hosting system. Compared to whole rock studies, the MIs approach shows advantages especially because it provides information on melt composition, volatile content, pressure and temperature at well-defined pre-eruptive stage. A large amount of geochemical data is available for the magmas generated in the Phlegraean Volcanic District (PVD), which is one of the most densely populated and high-risk volcanic areas of the world, but the knowledge provided by those data on their plumbing system, ascent, degassing and extrusion is limited. We investigated the glass/melt inclusions in olivines from the Solchiaro 1 volcanics, erupted on Procida Island, which is located along main tectonic alignment of the PVD. These products represent the least evolved magma of the PVD and could testify for the presence of the “basic” and deepest reservoir from which the Phlegraean magmas upraised and differentiated through various steps. Often invoked in literature, this “primitive” reservoir is basically uncostrained. We performed microprobe and microscopy measures to determine textural and compositional features of the MIs and host-minerals. The measures by Fourier Transform InfraRed spectroscopy provided the content of dissolved H2O and CO2, hence the volatile budget of magmas and entrapment pressures (i.e. depths of crystal growth). Recalculated crystallization depths for the Solchiaro 1 olivines result to be very deep (~350 MPa) and isobars obtained for the MIs describe a degassing trend with high CO2 content, of deep origin. Taking into account the geophysical data and the MIs studies on other Phlegraean products recently published, our dataset depicts a new framework for the evolution of the PVD plumbing system up to the present time that improves both the comprehension of magma evolution and migration through various reservoirs and the volcanic hazards assessment.

The Campi Flegrei (CF) caldera is one of the most dangerous quiescent volcanic systems in the world. Its activity mostly resulted in low-magnitude explosive eruptions, such as that of the Monte Nuovo tuff cone that represents the last eruptive event within the caldera (A.D. 1538). However, there have been more energetic Plinian events, e.g., the Agnano Monte Spina eruption (4.1 ka), and very highly explosive, caldera-forming eruptions, e.g., the Campanian Ignimbrite eruption (39 ka). Here, we integrate new and literature data on the groundmass texture and composition of pyroclastic products from the three above eruptions with the aim of unraveling how volatiles content, degassing mechanisms, and crystallization processes influence magma explosivity and eruption dynamics at CF. Previous studies indicate that the investigated rocks share similar major element bulk and phenocryst chemistry; also similar is the water content of their trapped melt inclusions. These observations suggest that the magmas feeding these eruptions had comparable physicochemical properties during storage in the shallow crust. However, our investigations indicate that the studied rocks differ in texture and composition of the groundmass and viscosity of the related magmas. We ascribe such differences to the variable style of volatile exsolution and outgassing from the melt, primarily in response to changes of the rate of magma ascent to the surface. We conclude that the magma ascent rate was the key parameter in driving explosive eruptions at CF, and we suggest that this parameter may be influenced by magma-water interaction and/or magma chamber geometry and replenishment.

The Neapolitan volcanic region is located within the graben structure of the Campanian Plain (CP), which developed between the western sector of the Appenine Chain and the eastern margin of the Tyrrhenian Sea. Two volcanic areas, spaced less than 10 km apart, are situated within the CP: the Somma - Vesuvius Volcano (SVV) and the Phlegraean Volcanic District (PVD). SVV is a typical stratovolcano, whereas PVD, including Campi Flegrei, Procida, and Ischia, is composed mostly of monogenetic centers. This contrast is due to different magma supply systems: a widespread fissure-type system beneath the PVD and a central-type magma supply system for the SVV. Volcanological, geophysical, and geochemical data show that magma viscosity, magma supply rate, and depth of magma storage are comparable at PVD and SVV, whereas different structural arrangements characterize the two areas. On the basis of geophysical data and magma geochemistry, an oblique-extensional tectonic regime is proposed within the PVD, whereas in the SVV area a compressive stress regime dominates over extension. Geophysical data suggest that the area with the maximum deformation rate extends between the EW-running 41st parallel and the NE-running Magnaghi-Sebeto fault systems. The PVD extensional area is a consequence of the Tyrrhenian Sea opening and is decoupled from the surrounding areas (Roccamonfina and Somma-Vesuvius) which are still dominated by Adriatic slab dynamics. Spatially, we argue that the contribution of the asthenospheric wedge become much less important from W-NW to E-SE in the CP. The development of the two styles of volcanism in the CP reflects the different tectonic regimes acting in the area. Copyright 2005 by the American Geophysical Union.