Publication Date:
2021-05-12
Description:
Ischia, a volcanic island located 18 miles SW of Naples (Southern
Italy), is a densely populated active caldera that last erupted in AD
1302. Melt inclusions in phenocrysts of the Vateliero and Cava
Nocelle shoshonite^latite eruptive products (6th to 4th centuries BC)
constrain the structure and nature of the Ischia deep magmatic feeding system.Their geochemical characteristics make Ischia a natural
borehole for probing the physico-chemical conditions of magma generation in mantle contaminated by slab-derived fluids or melts, largely
dominated by CO2.Volatile concentrations in olivine-hosted melt inclusions require gas^melt equilibria at between 3 and 18 km depth.
In agreement with what has already been demonstrated at the other
neighboring Neapolitan volcanoes (Procida, Campi Flegrei caldera
and Somma^Vesuvius volcanic complex), a major crystallization
depth at 8^10 km has been identified.The analyzed melt inclusions
provide clear evidence for CO2-dominated gas fluxing and consequent dehydration of magma batches stagnating at crustal discontinuities. Gas fluxing is further supported by selective enrichment in
K owing to fluid-transfer during magma differentiation.This takes
place under oxidized conditions (Fe3þ
/Fe 0·3) that can be
fixed by an equimolar proportion of divalent and trivalent iron in
the melt if post-entrapment crystallization of the host olivine is discarded.The melt inclusion data, together with data from the literature for other Neapolitan volcanoes, show that magmatism and
volcanism in the Neapolitan area, despite differences in composition and eruption dynamics, are closely linked to supercritical CO2-rich
fluids. These fluids are produced by devolatilization of subducting
terrigenous^pelagic metasediments and infiltrate the overlying
mantle wedge, generate magmas and control their ascent up to eruption. Geochemical characteristics of Ischia and the other Neapolitan
volcanoes reveal that the extent of fluid or melt contamination of the
pre-subduction asthenospheric mantle wedge was similar among
these volcanoes. However, differences in the isotopic compositions of
the erupted magmas (more enriched in radiogenic Sr at Ischia,
Campi Flegrei and Somma^Vesuvius with respect to Procida) and
the amount of H2O in the plumbing system of these volcanoes
(almost double at Ischia, Campi Flegrei and Somma^Vesuvius
than at Procida) reflect the different flow-rates of deep slab-derived
fluids or melts through the mantle wedge, which, in turn, control the
amount of generated magma.The high bulk permeability of the lithosphere below Ischia, Campi Flegrei and Somma^Vesuvius, determined by the occurrence of intersecting NW^SE and NE^SW
regional fault systems, favours fluid ascent and accumulation at
crustal levels, with consequent larger magma production and storage
than at Procida, located along the NE^SW system.
Description:
Published
Description:
951-984
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
Description:
4V. Processi pre-eruttivi
Description:
6A. Geochimica per l'ambiente e geologia medica
Description:
JCR Journal
Keywords:
CO2-fluxing
;
melt inclusions
;
redox state
;
trachybasalts
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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