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One of the main goals of studying melt inclusions (MI) is to constrain the pre-eruptive physical and chemical processes that have occurred in a magma reservoir at the micro-scale. Recently, several studies that focused on magmatic differentiation of volcanic systems produced detailed interpretations based on data from MI trapped at different times and locations in the plumbing system. Ideally, MI data should be collected and tested following the melt inclusion assemblage (MIA) protocol that consists of studying and analyzing groups of MI that were trapped at the same time, and, thus, at the same chemical and physical conditions. However, the rarity of MIA in juvenile volcanic phenocrysts precludes this methodology in many cases, leading to uncertainty concerning the validity of the MI as recorders of pre-eruptive conditions. In this study, we focused on MI from the Campi Flegrei (CF) and the Island of Procida (IP) volcanic systems in southern Italy, including data from this study and data from the literature. The database included MI hosted in sanidine, clinopyroxene, plagioclase, biotite and olivine, and, thus, represents melts trapped at various stages in the overall differentiation process. We developed a protocol to select the most reliable MI from a dataset associated with a single magmatic system. As a first step we compare MI data with bulk rock data for the same magmatic system. This comparison reveals that most MI show major element compositions that fall within or close to the range for bulk rocks – these MI are considered to be “normal”. Some MI show anomalous compositions and are not representative of the melt in equilibrium with the phenocryst host and were excluded from the data set. In the second step we selected only bubble-free MI from the previously identified “normal” MI to interpret the volatile evolution. In the third step we compare compositions of the “normal” bubble-free MI to compositions predicted by rhyolite-MELTS simulations, assuming a v

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

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.Th