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- PublicationOpen AccessConstraints on mantle source and interactions from helium-strontium isotope variations in Italian volcanism(2008-04-13)
; ; ; ; ;Martelli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Stuart, F. M.; SUERC, UK ;Ellam, R. M.; SUERC, UK; ; ; Helium isotope ratios of olivine and pyroxene from Plio-Quaternary volcanic rocks from Southern Italy (each of the seven Eolian Islands, Mt. Vulture, Etna, Ustica, Pantelleria), range from 2.3 to 7.1 Ra. A good correlation emerges with the 3He/4He of fumarolic fluids. Importantly the phenocryst 3He/4He correlate with whole rock Sr isotopes (0.70309-0.70711) reflecting the mixing of two sources. Crustal contamination of magmatic He isotopes is recorded only occasionally (e.g., pyroxenes from Vulcano). The He isotope values of Pantelleria, Etna, Iblei, Ustica, Alicudi and Filicudi (7.0 ± 0.6 Ra) define the mantle composition least affected by subduction. That these characterise volcanoes from a variety of tectonic regimes (subduction-related, intraplate, rifting) suggest a common origin of geochemical features and are consistent with a HIMU-type mantle that is either younger than the Cook-Austral island end-member, or one with lower 238U/204Pb. When merged with data from the Roman Comagmatic Province (Latium and Campania), a remarkably strong He-Sr isotope correlation is apparent. The general northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr and 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 since 30 Ma. 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.145 77 - PublicationRestrictedHelium–strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy(2004)
; ; ; ; ; ; ;Martelli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Stuart, F. M.; Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK ;Burgess, R.; Department of Earth Sciences, Manchester University, Manchester M13 9PL, UK ;Ellam, R. M.; Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; A study of the He isotopic ratios of fluid inclusions in olivine and pyroxene from the Roman Comagmatic Province (RCP),Italy, is presented together with 87Sr/86Sr isotope compositions of the whole rock or pyroxene phenocrysts. A clear covariation in He and Sr isotopes is apparent, with a strong northward increase in radiogenic He and Sr being evident. He and Sr isotopes ratios range from 3He/4He = 5.2 Ra and 87Sr/86Sr = 0.7056 in south Campania, to 3He/4He = 0.44 Ra and 87Sr/86Sr = 0.715905 in the northernmost Latium. Helium isotope ratios are significantly lower than MORB values and are among the lowest yet measured in subduction zone volcanism. The 3He/4He of olivine and pyroxene phenocryst-hosted volatiles appear to be little influenced by posteruptive processes and magma–crust interaction. The 3He/4He–87Sr/86Sr covariation is consistent with binary mixing between an asthenospheric mantle similar to HIMU ocean island basalts, and an enriched (radiogenic) mantle end member generated from subduction of the Ionian/Adriatic plate. The contribution of radiogenic He from metasomatic fluids and postmetasomatism radiogenic ingrowth in the wedge is strongly dependent on the initial He concentration of the mantle. Only when asthenosphere He concentrations are substantially lower than the MORB source mantle, and metasomatism occurred at the beginning of the subduction (f30 Ma), can ingrowth in the mantle wedge account for the 3He/4He of the most radiogenic basalts.378 86 - PublicationRestrictedBimodal magmatism produced by progressively inhibited crustal assimilation(2014)
; ; ; ; ; ; ; ;Meade, F.; Department of Earth Sciences, CEMPEG, Uppsala University, Villava¨gen 16, 752 36 Uppsala, Sweden ;Troll, V.; Department of Earth Sciences, CEMPEG, Uppsala University, Villava¨gen 16, 752 36 Uppsala, Sweden ;Ellam, R. M.; Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF Scotland, UK. ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Font, L.; Department of Petrology, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands ;Donaldson, C. H.; School of Geography and Geosciences, University of St Andrews, North Street, St Andrews, KY16 9AL Scotland, UK. ;Klonowska, I.; Department of Earth Sciences, CEMPEG, Uppsala University, Villava¨gen 16, 752 36 Uppsala, Sweden; ; ; ; ; ; The origin of bimodal (mafic–felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.433 99 - PublicationRestrictedConstraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism(2008-02-02)
; ; ; ; ; ;Martelli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Stuart, F.; Suerc ;Di Liberto, V.; Dip CFTA, Univ. Palermo ;Ellam, R.; Suerc; ; ; ; 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.254 33