Origin of primitive ultra-calcic arc melts at crustal conditions — Experimental evidence on the La Sommata basalt, Vulcano, Aeolian Islands

International audience; To interpret primitive magma compositions in the Aeolian arc and contribute to a better experimental characterization of ultra-calcic arc melts, equilibrium phase relations have been determined experimentally for the La Sommata basalt (Som-1, Vulcano, Aeolian arc). Som-1 (Na2O + K2O = 4.46 wt.%, CaO = 12.97 wt.%, MgO = 8.78 wt.%, CaO/Al2O3 = 1.03) is a reference primitive ne-normative arc basalt with a strong ultra-calcic affinity. The experiments have been performed between 44 and 154 MPa, 1050 and 1150 °C and from NNO + 0.2 to NNO + 1.9. Fluid-present conditions were imposed with H2O–CO2 mixtures yielding melt H2O concentrations from 0.7 to 3.5 wt.%. Phases encount…

Caratterizzazione chimica ed isotopica della carota MSK-C4 (Tirreno Meridionale)

Volatiles in pantellerite magmas: A case study of the Green Tuff Plinian eruption (Island of Pantelleria, Italy)

Abstract The Green Tuff (GT) Plinian eruption, the largest in magnitude at Pantelleria, erupted 3 to 7 km3 DRE of pantellerite magma and a small volume of trachyte. Fifty-nine anorthoclase-hosted melt inclusions from the two basal pumice members were analyzed by FT-IR spectroscopy in order to assess the pre-eruptive H2O content in the pantellerite melt. Microanalytical methods were used to determine major element, Cl, F and S contents. Melt inclusions and glassy groundmasses have a nearly homogeneous pantelleritic composition (peralkaline index = 1.9-2.2) and variable water contents ranging from 1.4 to as high as 4.2 wt %, i.e. much higher than the 1.4 wt % of earlier published studies. The…

Un approccio radiometrico e petrografico per l’analisi di campioni dei monti delle Madonie (Sicilia, Italia)

Una campagna di prelievo nella regione montagnosa delle Madonie (Sicilia) è stata recentemente effettuata per caratterizzare dal punto di vista dosimetrico zone con differenti caratteristiche litologiche. Al termine della campagna sono stati raccolti 41 campioni di terreno e rocce selezionati in base alla loro natura. Tutti i campioni sono stati poi triturati, essiccati e sigillati in beakers "Marinelli" per 20 giorni prima della misura per garantire il raggiungimento dell’equilibrio radioattivo tra 226Ra e 214Bi. Sono stati poi sottoposti a misure spettrometriche gamma con rivelatore a Ge di efficienza 35% per la determinazione delle concentrazioni dei radionuclidi presenti. Le caratterist…

MULTIVARIATE STATISTICAL TOOLS FOR THE RADIOMETRIC FEATURES OF VOLCANIC ISLANDS

The Aeolian Islands represents a Quaternary volcanic arc related to the subduction of the Ionian plate beneath the Calabrian Arc. The geochemical variability of the islands has led to a broad spectrum of magma rocks. Volcanic products from calc-alkaline (CA) to calc-alkaline high in potassium (HKCA) are present throughout the Archipelago, but products belonging to shoshonitic (SHO) and potassium (KS) series characterize the southern portion of Lipari, Vulcano and Stromboli. Tectonics also plays an important role in the process of the islands differentiation. In this work, we want to review and cross-analyze the data on Lipari, Stromboli and Vulcano, collected in measurement and sampling cam…

Pantelleria island (Strait of Sicily): volcanic history and geomorphological landscape

Pantelleria is a volcanic island located in the Strait of Sicily, 95 km far from the Sicilian coastline and 67 km from Cape Bon (Tunisia). The volcanological history of the island begins approximately 324 ka BP and the last eruptive event was a submarine eruption that occurred on 1891 A.D. Eruptive activity was characterized by seven very intense explosive events, the latest being the Green Tuff (44 ka). They have all produced ignimbrite sheets that covered large sectors of the island. The landscape of the island mirrors the variety of the eruptive styles and their interplay with volcano-tectonics. The most evident geomorphological features are represented by: (i) the mantle-like distributi…

Ricostruzione paleoclimatica degli ultimi 16.000 anni nella carota MSK12-C1 (Tirreno Meridionale)

Geochemistry and volatile content of magmas feeding explosive eruptions at Telica volcano (Nicaragua)

Telica volcano, in north-west Nicaragua, is a young stratovolcano of intermediate magma composition producing frequent Vulcanian to phreatic explosive eruptions. The Telica stratigraphic record also includes examples of (pre)historic sub-Plinian activity. To refine our knowledge of this very active volcano, weanalyzedmajor element composition and volatile content of melt inclusions fromsomestratigraphically significant Telica tephra deposits. These include: (1) the Scoria Telica Superior (STS) deposit (2000 to 200 years Before Present; Volcanic Explosive Index, VEI, of 2–3) and (2) pyroclasts from the post-1970s eruptive cycle (1982; 2011). Based on measurements with nanoscale secondary ion…

A radiometric and petrographic interpretation of discrepancies on uranium content in samples collected at Alte Madonie Mounts region (Sicily, Italy)

Abstract The main goal of this work is to evaluate a correlation between anomalous Uranium (U) content and petrographic features of some soil and rock samples collected at Alte Madonie Mounts region (North-central Sicily, Italy). A total of 41 samples of selected soils and rocks were collected, powdered, dried and sealed in “Marinelli” beakers for 20 days before the measurement to ensure that radioactive equilibrium between 226 Ra and 214 Bi was reached. Gamma-ray spectrometric analysis was used to quantify radioactivity concentrations. Mineralogical and chemical features of the samples were determined by X-ray Fluorescence (XRF), X-ray Diffractometry (XRD), Attenuated Total Reflection-Four…

Sul ritrovamento di tephra di composizione riolitica peralluminosa a largo del promontorio di Capo Vaticano (Calabria Occidentale, Tirreno Meridionale)

PETROLOGICAL AND EXPERIMENTAL CONSTRAINTS OF THE PRE-ERUPTIVE CONDITIONS OF LA SOMMATA BASALT AND BROWN TUFFS TEPHRA (AEOLIAN ISLANDS)

The principal focus of this thesis was the reconstruction of pre-eruptive conditions of two key eruptions at Vulcano island, the Brown Tuffs and the La Sommata, by combining the melt inclusion approach with phase equilibria derived by crystallization experiments. Brown Tuffs (the most energetic and widely distributed eruption of the Archipelago) were produced by several eruptions that occurred in a large age interval, 78-7.7 ka B.P. At Vulcano BT deposits crop out as proximal facies. La Sommata centre (age ca. 50 ka B.P.), is instead a basaltic scoria cone fed by one of the most primitive magmas of Aeolian Arc with ankaramitic affinity. Pyroxene-hosted melt inclusions on Lower and Intermedi…

Volcanic products of Lipari (Aeolian islands, Italy): Multivariate analysis of petrographic and radiometric data

Abstract A petrographic and radiometric study, along with statistical multivariate analysis of volcanic products of the island of Lipari (Aeolian islands, Italy) was carried out. The volcanological history of Lipari was reconstructed defining two stages (pre- and post-erosive stages) further on subdivided in four volcanic phases, each of which characterized by products with a particular chemical composition and separated by stratigraphic unconformities. The correlations between petrographic features, determined by X-ray fluorescence, and volcanological history of the island highlight a gradual differentiation with younger rocks showing a more acid chemical composition than the older ones. R…

A radiometric and petrographic approach to risk assessment at Alte Madonie Mounts region (Sicily, Italy)

The main goal of this work was to assess the radiological hazard at Alte Madonie Mounts region (north-central Sicily, Italy) in response to rumours of an increase in the incidence of cancer in this area. A correlation between the natural radionuclide contents and the petrographic features of the soil and rock samples was also evaluated. A total of 41 samples of selected soils and rocks were collected, powdered, dried and sealed in 'Marinelli' beakers for 20 d prior to measurement to ensure that a radioactive equilibrium between (226)Ra and (214)Bi had been reached. A gamma-ray spectrometer was used to quantify the radioactivity concentrations. To determine (238)U and (232)Th activities, the…

PETROLOGICAL AND EXPERIMENTAL CONSTRAINTS ON THE PRE-ERUPTIVE CONDITIONS OF LA SOMMATA BASALT AND BROWN TUFFS TEPHRA (AEOLIAN ISLANDS)

This work is focused on two key eruptions of Vulcano Island: 1) the most primitive magma of Vulcano erupted by the La Sommata scoria cone, a silica-undersaturated Ca-rich shoshonitic basalt with olivine-hosted primitive melt inclusions having an ultra-calcic character; 2) the most energetic eruptions of the whole Aeolian Archipelago, the Brown Tuffs (BT) eruptions, which produced several pyroclastic deposits, covering an ample age interval, spread out over a large portion of all Aeolian islands up to the northern coast of Sicily (Lucchi et al., 2008). By complementary studies of melt inclusions and experimental petrology, we pursued the following main objectives: (i) to constrain the pressu…

Melt inclusion study on the pantelleritic plinian eruption of the Green Tuff, Pantelleria Island.

Pantelleria Island is the type locality for the peralkaline rhyolitic rocks called pantellerites. In the last 50 ka, after the Plinian, caldera-forming, Green Tuff eruption, volcanic activity at Pantelleria consisted of effusive and mildly explosive eruptions which mostly vented inside and along the rim of the caldera producing silicic lava flows, lava domes and poorly dispersed pantelleritic pumice fall deposits. During the last two decades, a wealth of studies focused on melt inclusions in pantellerite magmas, all converging in underlying the H2O-rich character of these melts together with high contents of halogens. Recent study on the volatile content of pantellerites from Pantelleria yi…

Pre-Eruptive Conditions of La Sommata Basalt (Vulcano, Aeolian Islands): Constraints from Experimental Petrology.

One of the most primitive magma of Aeolian Arc is the basalt erupted (about 50 ka B.P.) by the La Sommata scoria cone at Vulcano; this is a silica-undersaturated (ne-normative) low-phyric (10-20 wt. %), Ca-rich (CaO = 13 wt. %) shoshonitic basalt (K2O = 2.28 wt.%) in which olivine phenocrysts host melt inclusions more primitive than whole rock composition and with an ultra-calcic character: CaO/Al2O3 > 1.4 [Métrich and Clocchiatti, 1996; Gioncada et al., 1998; Schiano et al., 2000]. Phenocrysts mainly include olivines (Fo92) and clinopyroxenes (Fs5). Plagioclase microlites (from An79 to An67) are the most abundant groundmass phase (45 wt. %), together with clinopyroxene (Fs11) and olivine (…