Chlorine as a Discriminant Element to Establish the Provenance of Central Mediterranean Obsidians

Chlorine is a minor element present in obsidians in quantities greater than in average igneous rocks. The chlorine concentration in obsidians is generally low, of the order of tenths of wt %, but it exhibits an appreciable differentiation among geological sources. Despite these characteristics, chlorine has rarely been taken into consideration as a possible indicator of obsidian provenance and it does not appear in the chemical analytical tables accompanying the geochemical characterisation of obsidian samples. In this work, after an overview of chlorine geochemistry and cycle, we present thirty-one new electron microprobe (EPMA) analyses, including Cl, of geologic obsidians sampled from the four sources of the Central Mediterranean, exploited in prehistoric times (Monte Arci, Palmarola, Lipari and Pantelleria). The results are compared with 175 new EPMA analyses, including Cl, of archaeological obsidians already characterised in previous work and of known provenance. As such it was possible to ascertain that each source has a characteristic chlorine concentration, showing the utility of its use in the studies of obsidian provenance. Furthermore, given that the solubility of chlorine in silicate melts is correlated to its alkali content, in particular sodium, we assessed the efficacy of simple binary graphs Cl vs Na2O to better constrain the provenance of the obsidian samples

Implementazione di un sistema GIS per la definizione della pericolosità associata alla risalita di fluidi endogeni nei Colli Albani

L’area nord occidentale del Distretto vulcanico dei Colli Albani è stata ripetutamente interessata negli ultimi anni da improvvise emanazioni di gas tra cui preponderante è la CO2.Spesso a queste manifestazioni si è associato uno sciame sismico di bassa magnitudo. In un caso, in concomitanza di emanazione di gas da un pozzo, si è anche registrata la morte di una persona. Gli studi geologici recenti evidenziano, inoltre, la ricorrenza in tempi recentissimi di fenomeni catastrofici di esondazione del lago di Albano da porsi in relazione alla presenza di abbondanti quantitativi di CO2 nelle sue acque. Le emanazioni di CO2 si verificano principalmente nell’area di Ciampino-Albano, nel settore occidentale del Distretto vulcanico, che quindi si pone come un settore di cui è necessario approfondire le conoscenze in modo da definirne lo stato di pericolosità. Questo è ancora di maggior rilievo se si considera che l’area di Ciampino, ormai a ridosso dell’urbe, si pone come suo naturale luogo di espansione urbana. L’area dei Colli Albani è stata oggetto di numerosi studi geologici anche specialistici ed è a tutt’oggi area di indagine per la valorizzazione e protezione delle sue risorse, prima tra tutte l’acqua. Si dispone pertanto di una mole di dati sia di superficie che di sondaggi più o meno profondi oltre che di informazioni del sottosuolo dedotte da indagini geofisiche. Questo ha reso possibile con l’ausilio di un GIS l’ideazione di una banca dati interattiva al fine di ottenere una carta della pericolosità associata alla risalita di CO2 nel settore compreso tra Ciampino e la Valle di Castiglione.Il settore è stato scelto come area campione per diversi motivi: prima di tutto perché è il settore dove recentemente si sono verificate le emissioni di gas. Secondariamente, perché localmente, è interessato dai depositi dell’esondazione del lago di Albano i quali sembra possano fungere da terreni impermeabili di copertura, “protettivi” nei confronti del gas; in alcuni casi si è verificata l’emanazione quando questa copertura è stata rimossa per effettuare opere antropiche.Infine questo settore, verso est, si congiunge all’area di Tivoli, storicamente nota come area ad emanazione di gas e di acque idrotermali.Per la realizzazione del GIS sono stati presi in considerazione diversi tematismi, ognuno dei quali ha portato alla realizzazione di una carta. Le carte hanno via, via interagito tra loro fino ad ottenere la carta definitiva della pericolosità. I tematismi scelti ed elaborati sono: Geologia di superficie, Aree di emanazione di CO2, Carta del tetto del substrato sedimentario, Permeabilità dei terreni, Andamento dell’acquifero.La carta della pericolosità si otterrà dunque interpolando per passi successivi i vari tematismi. L’area individuata dal Gis come quella esposta al maggior livello di pericolosità è,come previsto, quella di Ciampino. L’elaborazione ne ha però individuati i confini e messo in evidenza l’orientamento NW-SE. Inoltre è stato individuato un nuovo settore esposto allo stesso livello di pericolosità, non noto precedentemente, che è quello al margine ovest di Castiglione. Un altro vantaggio dell’elaborazione dei dati in ambiente GIS è quello di poter verificare le relazioni che esistono in ogni settore tra variabilità dello spessore che deve essere attraversato dal gas, permeabilità delle unità interessate, grado di fratturazione superficiale e geometria dell’acquifero. E’ evidente che ognuno di questi fattori ha un’impor

The effects of environmental parameters on diffuse degassing at Stromboli volcano: Insights from joint monitoring of soil CO2 flux and radon activity

Soil CO2 flux and 222Rn activity measurements may positively contribute to the geochemicalmonitoring of active volcanoes. The influence of several environmental parameters on the gas signals has been substantially demonstrated. Therefore, the implementation of tools capable of removing (or minimising) the contribution of the atmospheric effects from the acquired time series is a challenge in volcano surveillance. Here, we present 4 years-long continuousmonitoring (fromApril 2007 to September 2011) of radon activity and soil CO2 flux collected on the NE flank of Stromboli volcano. Both gases record higher emissions during fall–winter (up to 2700 Bq * m−3 for radon and 750 g m−2 day−1 for CO2) than during spring–summer seasons. Short-time variations on 222Rn activity aremodulated by changes in soil humidity (rainfall), and changes in soil CO2 flux that may be ascribed to variations in wind speed and direction. The spectral analyses reveal diurnal and semi-diurnal cycles on both gases, outlining that atmospheric variations are capable to modify the gas release rate fromthe soil. The long-termsoil CO2 flux shows a slow decreasing trend, not visible in 222Rn activity, suggesting a possible difference in the source depth of the of the gases, CO2 being deeper and likely related to degassing at depth of the magma batch involved in the February–April 2007 effusive eruption. To minimise the effect of the environmental parameters on the 222Rn concentrations and soil CO2 fluxes, two different statistical treatments were applied: the Multiple Linear Regression (MLR) and the Principal Component Regression (PCR). These approaches allow to quantify theweight of each environmental factor on the two gas species and showa strong influence of some parameters on the gas transfer processes through soils. The residual values of radon and CO2 flux, i.e. the values obtained after correction for the environmental influence, were then compared with the eruptive episodes that occurred at Stromboli during the analysed time span (2007–2011) but no clear correlations emerge between soil gas release and volcanic activity. This is probably due to i) the distal location of the monitoring stations with respect to the active craters and to ii) the fact that during the investigated period no major eruptive phenomena (paroxysmal explosion, flank eruption) occurred. Comparison of MLR and PCR methods in time-series analysis indicates thatMLR can bemore easily applied to real time data processing in monitoring of open conduit active volcanoes (like Stromboli) where the transition to an eruptive phase may occur in relatively short times.This researchwas partly funded by ItalianMinistry of University and Research (MIUR) and by University of Torino-Fondazione Compagnia di San Paolo. Additional fundswere provided by the Italian “Presidenza del Consiglio dei Ministri–Dipartimento della Protezione Civile (DPC)” through the DEVnet Project (a cooperative program between the Departments of Earth Sciences of the University of Torino and the University of Florence) and through the “Potenziamento Monitoraggio Stromboli” project. Additional funds for improving our computing hardware were provided by Fondazione Cassa di Risparmio di Torino.Published65-784V. Processi pre-eruttiviJCR Journa

Geochemistry of the mantle source and magma feeding system beneath Turrialba volcano, Costa Rica

Turrialba volcano lies in the southern sector of the Central American Volcanic Front (CAVF) in Costa Rica. The geochemistry of major and trace elements, and Sr and Nd isotopes of a selected suite of volcanic rocks ranging in composition from basaltic andesite to dacite and belonging to the last 10ka of activity of Turrialba volcano is described, together with the He-, Ne-, and Ar-isotope compositions of fluid inclusions hosted in olivine and pyroxene crystals. Most of the variability in the rock chemistry is consistent with typical trends of fractional crystallization, but there is an outlying group of andesites that displays an adakite-like composition (with a consistent depletion in high-field-strength elements and a marked enrichment in Sr) and low 3He/4He ratios (7.0-7.2 Ra). The trace-element composition of these rocks is typical of subduction-related magmas influenced by an OIB-like component at the source associated with the subduction of the Galapagos seamounts. The 87Sr/86Sr (0.703612-0.703678) and 143Nd/144Nd (0.512960-0.512984) ratios of the bulk rocks vary within narrow ranges, and are among the least-radiogenic isotope signatures of the CAVF volcanoes. The 3He/4He ratios measured in fluid inclusions hosted in olivine crystals (up to 8.1 Ra) are among the highest for the CAVF, and indicate that radiogenic 4He from fluids derived from the subducting slab contribute negligibly to the mantle wedge. The difference in He isotopes between most of studied rocks and those showing adakite-like features reasonably reflects two distinct components in the local mantle: (1) a MORB-like component, characterized by the highest He-isotope ratios (7.8-8.1 Ra), and (2) an OIB-like component, characterized by lower He-isotope ratios (7.0-7.2 Ra), coming from the subduction of the Galapagos seamounts. An overview at the regional scale indicates that high He-isotope ratios are peculiar to the two extreme sectors of the CAVF (Costa Rica to the south and Guatemala to the north), whereas in the central sector (Nicaragua) the magma source is probably contaminated by slab fluids.For the past few years Turrialba volcano has been in a volcanic unrest phase that has included a series of explosions, the most recent of which occurred between October 2014 and May 2015. The volcano is subject to an ongoing safety alert due to the possibility of a magmatic eruption. One of the crucial questions to be addressed is the kind of eruption that can be expected, and hence what type of magma is likely to be involved. The high 3He/4He ratios (7.8-8.0 Ra) measured during 2011 at high-temperature fumaroles of Turrialba craters are comparable to those measured in fluid inclusions of basaltic andesites that erupted in 1864-1866, suggesting that the magma currently feeding the shallow plumbing system has similar geochemical characteristics to the most recently erupted magma

Anomalous gas emission offshore from Panarea Island (Aeolian Arc, Italy)

Panarea Island is located in the eastern sector of the Aeolian arc at only 20 km from the active volcano of Stromboli. Its recentmost volcanic products date back to about 50 ka but a probable submarine eruption occurred there in 126 B.C. Near to volcanic islets 3 km E of Panarea, on 3 November 2002 an impressive submarine gas emission began from several points at a depth 8-20 m. The strongest gas emission, with jet velocity of 1 m/s, occurred from a small depression, possibly produced by a weak submarine phreatic explosion. Most of the gas was emitted from NE-SW trending fissures, whose direction matches with the main tectonic lineament of the Panarea- Stromboli sector. Only a very weak local seismicity was recorded. Gas was sampled and the physico-chemical characteristics of the seawater (T, pH, Eh, dissolved O2,) were measured in two campaigns carried out in November and in December. Gas mostly consists of CO2 (95-98.2 vol % ) and H2S (0.7-2%). Compared with previous chemical data on the submarine fumaroles of the same area, the 2002 emission is characterized by a marked increase of H2 and a decrease of the CH4/CO ratio. These data indicate the presence of high-temperature components with a likely magmatic provenance raised from a pressurized system through newly opened fractures. The sea water was chemically modified over a wide area, as indicated by the low pH and Eh values. In the first months of 2003 the gas emission started to decline, but it was still clearly visible four months after its beginning. This phenomenon recalled the attention on the volcanic hazard related to a possible submarine eruption near Panarea, where over 10,000 people live in the tourist season

Integrated Surveys Of Active Volcanoes From Airborne, Bathymetric and Ground Based Data: The Examples Of Panarea and Albano (Italy).

Esempi di applicazioni di metodologie di rilievo delle superfici per il monitoraggio di aree vulcanich

Conditions for long-lasting gas eruptions: The 2013 event at Fiumicino International Airport (Rome, Italy)

A hazardous gas eruption from two very close shallow boreholes occurred near the Fiumicino International Airport of Roma (Italy) from August to December 2013. The erupted gas was mostly CO 2 of deep origin and gas output was high and sustained over time reaching values of nearly 20 t day•1. After 3 months, the gas flux was still above 5 t day•1 and was only stopped in December 2013 by long and expensive works of closure of the boreholes. The gas eruption was uncommon as being associated with the building of two mud volcanoes. This style of sustained deep CO 2 eruptions contrasts with the more common short-lived eruptions of shallow biogenic methane-dominated gas pockets. In this work, we present the chronology of the event, the results of geological, geochemical, and geophysical monitoring and a numerical modeling. We propose that the August-December 2013 sustained and prolonged event does not relate to the simple degassing of a shallow, isolated pocket of gas. On the contrary, it reflects very specific conditions in a shallow reservoir (hosted in a 10 m thick gravel layer at –40 m within the Tiber river delta deposits), related to the interplay between the total pressure and the fraction of free CO 2 initially present, across very narrow value ranges around 0.59 MPa and 0.18, respectively. The coexistence of short-lived and long-lived eruptions from the same reservoir suggest that these conditions are not achieved everywhere in the gas reservoir, despite its homogeneous properties. This consideration implies either a pressure compartmentalization of the reservoir, or the occurrence of a transient, possibly associated with an impulsive release of gas from greater depths. The involvement of deeper and larger gas reservoirs connected along faults is evidenced by geophysical investigations. This conceptual model bears significant implications for gas hazard studie