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Mount Somma-Vesuvius is a stratovolcano that represents a geological hazard to the population of the city of Naples and surrounding towns in southern Italy. Historically, volcanic eruptions at Mt. Somma-Vesuvius (SV) include high-magnitude Plinian eruptions, such as the infamous 79CE eruption that occurred after 295 years of quiescence and killed thousands of people in Pompeii and surrounding towns and villages. The last eruption at SV was in 1944 and showed a Volcanic Explosivity Index (VEI) of 3 (0.01km3 of volcanic material erupted). Following the 1944 eruption, SV has been dormant for the past nearly 79 years, with only minor fumarolic and seismic activity. During its long history, centuries of dormancy at SV have ended with Plinian eruptions (VEI 6) that signal the beginning of a new cycle of eruptive activity. Thus, the current dormancy stage demands a need to better understand the mechanism involved in high-magnitude eruptions in order to better predict future eruption magnitude and style. Despite centuries of research on the SV volcanic system, many questions remain, including the evolution of magmatic volatiles from deep primitive magmas to shallower more evolved magmas. Developing a better understanding of the physical and chemical processes associated with volatile evolution at SV can provide insights into magma dynamics and the mechanisms that trigger highly explosive eruptions at SV. In this study, we present new data for the pre-eruptive volatile contents of magmas associated with four Plinian and two inter-Plinian eruptions at SV based on analyses of reheated melt inclusions (MIs) hosted in olivine. We correct the volatile contents of bubble-bearing MIs by taking into account the volatile contents of bubbles in the MIs. We recognize two groups of MIs: one group hosted in high-Fo olivine (Fo85-90) and relatively rich in volatiles and the other group hosted in low-Fo olivine (Fo70-69) and relatively depleted in volatiles. The correlation between volatil

The large-scale Yaogangxian W deposit, located in central of the Nanling metallogenic belt, South China, comprises independent quartz vein-type and skarn-type W mineralization. Wolframite-bearing quartz veins occur invariably in metasandstone and slate to the northwest of the Yaogangxian granitic intrusion, whereas scheelite-skarn are mainly hosted by the limestone to the east. The vertical extension of single wolframite-bearing quartz vein can reach up to 1000 m and we focused on the vein samples collected from the deepest level (26 level) which likely recorded early magmatic fluids. For skarn mineralization, two scheelite precipitation stages were recognized, namely scheelite-1 in retrograde stage and scheelite-2 from sulfide-stage. To reveal the fluid sources and characteristics of two mineralizing systems, detailed petrography and microthermometry analyses were carried out on fluid inclusion assemblages (FIA) in scheelite, wolframite and their coexisting quartz. Fluid compositions were obtained from individual fluid inclusion (FI) in ore and gangue minerals via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. These data aid elucidation on the source and nature of fluids in the two distinct W mineralization styles. The chemical compositions of FIs hosted in wolframite and scheelite points to a common magmatic source. The fluid in the scheelite ore section exhibits lower As and B than the wolframite ore section, indicating that boiling may have occurred at early skarn stage. Fluid evolution in the two mineralizing systems suggest that formation of diverse W mineralization styles is mainly controlled by different host lithology and fluid processes. In the wolframite ore section, ore-forming fluid recorded in the deepest level of vein show elevated As, B, K and Rb contents than previously reported ore-forming fluid obtained from the tip of the vein. This likely indicate absence of intensive fluid immiscibility in the deep during wolf

Several recent models that have been put forth to explain bradyseism at Campi Flegrei (CF), Italy, are discussed. Data obtained during long-term monitoring of the CF volcanic district has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically; these data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-102 yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (103-104 yr) magmatic system enclosed by an impermeable carapace (A layer). Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when the systems are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation that seals cracks and serves to isolate the two reservoirs. Faults and fractures promote outgassing and redu

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

The Phlegrean Volcanic District (PVD) consists of Campi Flegrei (CF), Procida, and Ischia volcanic fields in Southern Italy. The recent unrest crisis of CF at the PVD demands a more detailed understanding of its deep magmatic system to better understand if a new eruption is imminent. Despite the large amount of work published relative to the PVD, there are still many open questions related to (1) the evolution of the magmatic vapor phase (MVP) directly exsolving from magmas at different times and different places below the PVD and (2) the source of this magmatism. Among the investigative tools that can be used to answer these questions about the PVD, melt inclusions (MIs) have been widely used, especially in the last two decades. In this chapter, I compare the MI data from the literature related to CF, Procida, and Ischia, and I highlight three main points based on this comparison. The first is that only a few MI show quasiprimitive composition, and these can be compared to investigate the magma sources below the three different localities of the PVD. This comparison highlights that the same magma source could be present below the three localities of the PVD at different times. The second point is that some of the more evolved MIs show divergence from the bulk rock trend. This divergence is indicative of natural reheating before eruptions, driven either by hotter magma recharging or by crystal settling. It is important to note that this behavior is found in MI hosted in sanidine of the highest magnitude eruption (the Neapolitan Yellow Tuff). The last point is that many MI in the literature are shown as bubble-bearing, but volatile contents of bubble are not taken into account. Thus, more research is needed to test interpretations of preeruptive volatile contents based on MIs.

We present a summary of the results obtained on more than 25 years of research achieved on Campi Flegrei (CF) past eruptions, focusing our attention on the role played by fluids in the magmatic system based on fluid (FI) and melt inclusions (MI). Particularly FI and MI data from subvolcanic igneous systems in the CF area provide valuable information on the nature of fluid and melt phases trapped during the late evolutionary stages of the alkaline magmatic systems. They also document liquid immiscibility at pre-eruptive magma conditions and furnish evidence of high salinity fluids (brines) exsolving directly from magma in the upper part of the plumbing system at the magmatic/hydrothermal transition and playing critical roles in ore metal transport. CF volcanic system can be interpreted as representing a modern analogue of low sulfidation epithermal deposits or a porphyry copper system. This interpretation led to the formulation of a model to explain ground movements (bradyseism) in the CF. Finally new finding for the estimations of pre-eruptive volatile contents in CF through MI are discussed. MI are the only direct samples to measure volatile contents of undegassed melt at subvolcanic conditions. Since the depth of formation of MI is estimated using H2O-CO2-silicate melt solubility models, it is important to emphasize that, to obtain a more accurate measure of the preeruptive CO2 concentration, not only the CO2 in the glass but also in the bubble have to be measured otherwise the minimum CO2 content in MI is obtained.

Clinopyroxene and olivine are ubiquitous phases in Somma-Vesuvius (SV) volcanics and for the first time they were systematically studied in several products younger than 40 ka. In this manuscript chemical compositions (major, trace and rare earth elements) of a large set of olivine and clinopyroxene crystals from selected rock samples are presented and discussed. Fourteen pumice samples from Plinian pyroclastic deposits as well as three scoriae and eight lava samples from inter-Plinian deposits were collected. A representative number of olivine and clinopyroxene crystals (n ~ 50) were selected for each sample and analysed by electron microprobe and laser ablation inductively coupled plasma mass spectrometer, resulting in a large database, which is now available to the scientific community. All studied eruptive products contain olivine and clinopyroxene crystals spanning a wide range of compositions. Olivines show Fo content varying from 91 to 68, while clinopyroxenes display Mg# ranging from 93 to 71. In samples younger than A.D. 79, the more evolved (Mg#82–72) clinopyroxene crystals show clear Ca enrichment (~23.5–24.5 wt% CaO) with respect to those from older samples (before-A.D.79, ~23–21 wt% CaO). The results corroborate disequilibrium between olivine, clinopyroxene and the hosting melt, and an increasing role of carbonate assimilation in SV magma evolution in the last 2 ka. The database here produced is thought as a share product that makes available mineral data and can be used for further studies by researchers to investigate geochemical evolution of the SV system.