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This review paper is intended to be a guideline to novices on how to conduct research on silicate melt inclusions in volcanic environments, which analytical techniques are more suitable to gather the desired data and the major pitfalls scientist may encounter. Silicate melt inclusions (SMIs) are small quantities of silicate melt that are trapped in minerals during their growth or crystallization. They contain liquids formed in equilibrium with their host minerals and therefore record the liquid line of descent of magmatic systems. Upon trapping, SMIs become ideally closed to the surrounding environment, and behave as time capsules, giving important information about processes that originated magmas and the nature of their mantle source. A melt inclusions investigation is composed of several steps: (1) a detailed petrographic study to characterize and select representative SMIs, with the aim of identifying Melt Inclusions Assemblages (MIA), the only reliable tool to assess that SMIs obey Roedder's rules and have not re-equilibrated following entrapment; (2) a careful preparation of samples for re-heating experiments and microanalysis; (3) high temperature studies in order to homogenize the SMIs and be able to perform chemical analysis; (4) interpretation of SMIs data, which should always be compared with bulk rock composition and relevant experimentally derived liquid compositions. We suggest that the search for good SMI candidates for study will be achieved by good petrographic analysis of SMIs and detailed petrographic information (size, shape, appearance, position relative to the host and other SMI within the same host). If the goal of a SMIs study is to determine volatile concentrations, assessing the relative time of trapping among SMIs is of paramount importance, as it allows understanding if the variation in volatile concentrations is consistent with a certain magmatic physical–chemical process. Researchers that choose to work with SMIs face several challenges. SMIs are not always hosted in all samples or they can be difficult to recognize (mostly due to their small size). Additionally, due several processes, such as post-entrapment crystallization, boundary layer and sampling melt heterogeneity at the micron scale, they may not be representative of the original trapped melt composition. [ABSTRACT FROM AUTHOR]

The Campanian Plain in southern Italy has been volcanically active for at least the last 300 ka. The Campanian Ignimbrite (CI) erupted at 39.3 ka, has a volume of ≥ 310 km 3 and a great areal extent. However, significant, but scattered deposits of older ignimbrites underlie the CI and document a long history of volcanism. We examined the mineralogy and geochemistry of 11 older ignimbrite strata by optical petrography, electron microprobe, scanning electron microscope, X-ray diffraction, and various whole-rock geochemical techniques. We have analyzed strata at Durazzano (116.1 ka), Moschiano (184.7 ka), Seiano Valley (245.9 and 289.6 ka), and Taurano — Acqua Feconia (157.4, 183.8, 205.6, and 210.4 ka) that have been previously dated on unaltered sanidine. The older ignimbrites are highly altered with loss on ignition (LOI) that ranges from 17 to 8 wt%. Whole-rock compositions reflect variable element mobility during weathering; e.g., CaO is enriched and Na 2 O depleted relative to hydration. X-ray diffraction identified major chabazite, kaolinite, and illite alteration products in some samples. Rhabdophane-(Nd), usually intergrown with chabazite and Mn-carbonate, indicates that some LREE were also mobilized during weathering. The phenocryst mineralogy is typical for Campanian Plain (CP) magmas and consists of plagioclase (An 88 Ab 11 Or 1 to An 32 Ab 63 Or 5 ), potassium feldspar (Or 40 Ab 57 An 3 to Or 79 Ab 18 An 3 ), biotite (TiO 2 = ~ 4–7 wt%, BaO = up to 2 wt%, F = up to 2 wt%), diopside (Ca 47 Mg 47 Fe 6 to Ca 48 Mg 29 Fe 23 ), and titaniferous magnetite. Relatively immobile trace elements Zr, Hf, Th, Ta, V, and Nb were used to investigate element abundance and ratio compared to the Campanian Ignimbrite and other CP magmas. Zr/Hf of the older ignimbrites is similar to that of the CI, but Ta is depleted relative to Th and V is enriched compared to CI. Th/Ta and Nb/V distributions for most of the older ignimbrites are similar to those in the Neapolitan Yellow Tuff with the exception of the sample MS-1 from Moschiano that is more evolved and similar to Campanian Ignimbrite. All older ignimbrite Zr/Hf (w/w) and many Nb/Ta (w/w) ratios are superchondritic that suggests that the older ignimbrites represent fractional crystallization products of parental magmas generated from enriched mantle without significant addition of continental crust. [ABSTRACT FROM AUTHOR]

Soil geochemistry is often investigated by considering a large number of variables, including major, minor and trace elements. Some of the variables are usually highly correlated due to coherent geochemical behaviour, but the effect of anthropic factors tends to increase data variability, sometimes obscuring natural relationships governing their distributions. In this framework it may be difficult to identify geochemical features linked to natural phenomena as well as to separate geogenic anomaly from the anthropogenic ones. Consequently the identification of background/baseline values may be seriously compromised. However, knowledge about these reference terms is fundamental to manage and protect natural resources on different scales. Moreover, adequate estimations of background/baseline values are possible only if a sufficient number of chemical analyses are stored in complex repositories. In this contribution the multi-element data archive of the Campania Region (Southern Italy) was explored from the CoDA (Compositional Data Analysis) multivariate perspective to characterise its structure. The archive contains abundance data of Al, As, B, Ba, Ca, Co, Cr, Cu, Fe, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, Th, Ti, V and Zn (mg/kg) determined in 3535 new topsoils as well as information on coordinates, geology and land cover. Under CoDA the proportionality features of abundance data are fully taken into account enhancing their relative multivariate behaviour in the correct sample space. Results indicate that the structure of the whole matrix appears to be constituted by a core that geographically is mainly given by topsoils developed on volcanic materials and several outlier compositions whose origin is different. Anomalous compositions can originate from the robust barycentre all around when the following conditions are present: 1) high Na–K volcanic products, 2) limestones and dolostones with their terrigenous component, 3) flysch deposits or 4) fertiliser contribution. The (1 × D ) robust barycentre of the whole dataset together with the variation array of the core represents the most frequent (1 × D ) multi-element vector as well as the proportionality relationships among its components. It might be considered a compositional baseline. [ABSTRACT FROM AUTHOR]