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Authors: Mormone, A.* 
Piochi, M.* 
Bellatreccia, F.* 
De Astis, G.* 
Moretti, R.* 
Della Ventura, G.* 
Cavallo, A.* 
Mangiacapra, A.* 
Title: A CO2-rich magma source beneath the Phlegraean Volcanic District (Southern Italy):
Journal: Chemical Geology 
Series/Report no.: /287(2011)
Issue Date: 13-Jun-2011
DOI: 10.1016/j.chemgeo.2011.05.019
Keywords: Melt inclusions
Phlegraean Volcanic District
CO2-rich magma source
Subject Classification02. Cryosphere::02.01. Permafrost::02.01.08. Instruments and techniques 
04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes 
04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks 
04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology 
04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry 
04. Solid Earth::04.04. Geology::04.04.11. Instruments and techniques 
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas 
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks 
05. General::05.02. Data dissemination::05.02.01. Geochemical data 
05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions 
Abstract: We present a study of olivine-hosted glass/melt inclusions (MIs) in the most primitive rocks erupted at Procida Island, within the Phlegraean Volcanic District (PVD), Southern Italy. MIs were analyzed by combined Scanning Electron Microscopy coupled with Energy Dispersive X-ray-detectors, Wavelength Dispersive X-rayequipped Electron Microprobe and Fourier Transform Infrared (FT-IR) Spectroscopy; notably, the novel Focal- Plane-Array mode provided high-resolution FT-IR images evidencing the distribution of the C–H–O species across samples. Olivines range in composition from Fo85 to Fo90, do not show chemical zoning and are totally anhydrous. The majority of the MIs are glassy, while only few are completely crystallized. Some MIs, however, show the occurrence of crystal nuclei, i.e., nano- to micro-sized pyroxenes and oxides, and appear as lowcrystallized MIs. The glass of crystal-free and low-crystallized MIs shows K-affinity and a compositional range along the basalt, trachy-basalt, shoshonite, tephrite basanite and phono-tephrite array. H2O and CO2 contents up to 2.69 wt.% and 2653 ppm, respectively, define a major degassing trend with small isobaric deviations. The collected data allow recalculating entrapment pressures from ~350 MPa to b50 MPa and suggest that the magma ascent was dominated by degassing. Crystallization was aminor process, likely also consequent to local CO2-fluxing. Mingling occurred between variable degassed and crystallized magma portions during decompression. The geochemical and isotopic data of Procida glasses and rocks, and the compositional relationship between our MIs and those from slightly more evolved and radiogenic Phlegraean products, indicate that Procida basalts are an adequate parental end-member for the PVD. Our data suggest that a CO2- rich magma source was stored at depths of at least 13–14 km (i.e., 350 MPa) beneath the PVD. Fast ascent of magma batches directly started from this depth shortly before PVD trachy-basaltic to shoshonitic eruptions. Such results have implication on volcanic hazard assessment in the PVD area.
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