Publication Date:
2017-04-04
Description:
Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from
southern Italy (seven Aeolian Islands, Mt. Vulture, Etna, Ustica, and Pantelleria) range from 2.3 to 7.1 Ra.
Importantly, the phenocryst 3He/4He correlate well with whole rock Sr isotopic composition (0.70309–
0.70711), reflecting the mixing of two sources. A significant contribution of He from crustal contamination
is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman
Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general
northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr (and a decrease in 143Nd/144Nd and
206Pb/204Pb) that is due to increasing metasomatic enrichment of the mantle wedge via subduction of the
Ionian-Adriatic plate. Calculations based on the ingrowth of 4He in the wedge and on the 4He content of
the subducting crust show that mechanisms of enrichment in radiogenic He are effective only if the wedge
is strongly depleted in He relative to best estimates of the depleted mantle. This can be accommodated if
the process of metasomatism by the subduction fluids depletes the mantle wedge. The 3He/4He of
Pantelleria, Etna, Iblei, Ustica, Alicudi, and Filicudi basalts (7.0 ± 0.6 Ra) define the mantle composition
least affected by subduction-related metasomatism. Although these volcanoes are from a variety of tectonic
regimes (subduction-related, intraplate, rifting), their similarities suggest a common origin of geochemical
features. Their characteristics are consistent with a HIMU-type mantle that either is younger than the Cook-
Austral island end-member or has a lower 238U/204Pb.
Description:
Published
Description:
Q02001
Description:
1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
Description:
JCR Journal
Description:
reserved
Keywords:
helium
;
strontium
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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