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

Lanzo, Giovanni; Landi, Patrizia; Rotolo, Silvio G.

doi:10.1016/j.jvolgeores.2013.06.011

Cited by 30 publications

(51 citation statements)

References 46 publications

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“…Both phonolitic units contain titanite, which has high mineral/melt partition coefficients for REE, Nb and Ta (Olin and Wolff, 2012;Wörner et al, 1983); in contrast, clinopyroxene is the only phase in the Green Tuff with high partition coefficients for REE (Neave et al, 2012). Maximum water contents for these units are in the same range as the rhyolitic examples above, indicating that the most highly differentiated portions were at, or close to, saturation (Harms and Schmincke, 2000;Lanzo et al, 2013;Olin and Wolff, 2010).…”

Section: Alkaline Systemsmentioning

confidence: 93%

Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

Wolff

Ellis

Ramos

et al. 2015

Lithos

116

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Section: Alkaline Systemsmentioning

confidence: 93%

Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

Wolff

Ellis

Ramos

et al. 2015

Lithos

116

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“…The pressure inferred from melt inclusions trapped in phenocrysts of the GT pantelleritic basal member (i.e. first ejected) is 0Á5-0Á6 kbar (Lanzo et al, 2013), providing a lower pressure bound. Our results corroborate geophysical constraints, which suggest the existence of a magma reservoir at a depth of about 4 km below Pantelleria.…”

Section: Pre-eruption Conditions Of Trachytic Magmas At Pantelleriamentioning

confidence: 98%

“…Melt inclusions trapped in phenocrysts of alkali basalts yield water contents (H 2 O melt) ranging from 0Á8 to 1Á6 wt % and CO 2 up to 980 ppm (Gioncada & Landi, 2010). Water contents in MI within phenocrysts of pantelleritic magmas vary between 2 and 4Á5 wt % (Lowenstern & Mahood, 1991;Gioncada & Landi, 2010;Neave et al, 2012;Lanzo et al, 2013). The corresponding pressures of volatile saturation are < 2 kbar, being consistent with both experimental (Di Carlo et al, 2010) and geophysical (Mattia et al, 2007) constraints, altogether suggesting the existence of a shallow magma reservoir at a depth of $4 km (1 kbar for an average crustal density of 2Á6 g cm -3 ).…”

Section: Petrological Background: the Origin Of Pantellerites And Prementioning

confidence: 99%

“…Recent petrological work has helped to define the temperature range and redox conditions of comenditic to pantelleritic magmas (Scaillet & Macdonald, 2001, 2003White et al, 2005White et al, , 2009Di Carlo et al, 2010) as well as their pre-eruptive volatile contents (e.g. Gioncada & Landi, 2010;Neave et al, 2012;Lanzo et al, 2013). In contrast, little is known about the conditions of magma storage and evolution of the associated trachytes.…”

Section: Introductionmentioning

confidence: 99%

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Phase Equilibria of Pantelleria Trachytes (Italy): Constraints on Pre-eruptive Conditions and on the Metaluminous to Peralkaline Transition in Silicic Magmas

Romano

Andújar

Scaillet

et al. 2018

Journal of Petrology

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The relationships between trachytes and peralkaline rhyolites (i.e. pantellerites and comendites), which occur in many continental rift systems, oceanic islands and continental intraplate settings, is unclear. To fill this gap, we have performed phase equilibrium experiments on two representative metaluminous trachytes from Pantelleria to determine both their pre-eruptive equilibration conditions (pressure, temperature, H 2 O content and redox state) and liquid lines of descent. Experiments were performed in the temperature range 750-950 C, pressure 0Á5-1Á5 kbar and fluid saturation conditions with XH 2 O [¼ H 2 O/(H 2 O þ CO 2)] ranging between zero and unity. Redox conditions were fixed below the nickel-nickel oxide buffer (NNO). The results show that at 950 C and melt water contents (H 2 O melt) close to saturation, trachytes are at liquidus conditions at all pressures. Clinopyroxene is the liquidus phase, being followed by iron-rich olivine and alkali feldspar. Comparison of experimental and natural phases (abundances and compositions) yields the following pre-eruptive conditions: P ¼ 1 6 0Á5 kbar, T ¼ 925625 C, H 2 O melt ¼ 2 6 1 wt %, and fO 2 between NNO-0Á5 and NNO-2. A decrease in temperature from 950 C to 750 C, as well as of H 2 O melt , promotes a massive crystallization of alkali feldspar to over 80 wt %. Iron-bearing minerals show gradual iron enrichment when T and fO 2 decrease, trending towards the compositions of the phenocrysts of natural pantellerites. Despite the metaluminous character of the bulk-rock compositions, residual glasses obtained after 80 wt % crystallization evolve toward comenditic compositions, owing to profuse alkali feldspar crystallization, which decreases the Al 2 O 3 of the melt, leading to a consequent increase in the peralkalinity index [PI ¼ molar (Na 2 O þ K 2 O)/Al 2 O 3 ]. This is the first experimental demonstration that peralkaline felsic derivatives can be produced by low-pressure fractional crystallization of metaluminous mafic magmas. Our results show that the pantelleritic magmas of basalt-trachyte-rhyolite igneous suites require at least 95 wt % of parental basalt crystallization, consistent with trace element evidence. Redox conditions, through their effect on Fe-Ti oxide stabilities, control the final iron content of the evolving melt.

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“…There are few constraints on the architecture and dynamics of peralkaline magma reservoirs, and little is known about the types of geophysical signals such magma bodies would generate. Peralkalinity, defined as having an excess of alkalis with respect to aluminium (molar (Na 2 O + K 2 O)/Al 2 O 3 > 1; Shand, ), has a strong influence on melt rheology, and thus magma behavior (Lanzo et al, ; Neave et al, ; Stevenson & Wilson, ). The elevated alkali content of peralkaline melts, coupled with high dissolved halogen contents (Barclay et al, ), results in peralkaline liquids having much lower viscosity (by 2 to 3 log units) compared to their metaluminous counterparts, particularly at temperatures approaching the solidus (di Genova et al, ).…”

Section: Introductionmentioning

confidence: 99%

Mixing and Crystal Scavenging in the Main Ethiopian Rift Revealed by Trace Element Systematics in Feldspars and Glasses

Iddon

Jackson

Hutchison

et al. 2019

Geochem Geophys Geosyst

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For many magmatic systems, crystal compositions preserve a complex and protracted history, which may be largely decoupled from their carrier melts. The crystal cargo may hold clues to the physical distribution of melt and crystals in a magma reservoir and how magmas are assembled prior to eruptions. Here we present a geochemical study of a suite of samples from three peralkaline volcanoes in the Main Ethiopian Rift. While whole‐rock data show strong fractional crystallization signatures, the trace element systematics of feldspars, and their relationship to their host glasses, reveals complexity. Alkali feldspars, particularly those erupted during caldera‐forming episodes, have variable Ba concentrations, extending to high values that are not in equilibrium with the carrier liquids. Some of the feldspars are antecrysts, which we suggest are scavenged from a crystal‐rich mush. The antecrysts crystallized from a Ba‐enriched (more primitive) melt, before later entrainment into a Ba‐depleted residual liquid. Crystal‐melt segregation can occur on fast timescales in these magma reservoirs, owing to the low‐viscosity nature of peralkaline liquids. The separation of enough residual melt to feed a crystal‐poor postcaldera rhyolitic eruption may take as little as months to tens of years (much shorter than typical repose periods of 300–400 years). Our observations are consistent with these magmatic systems spending significant portions of their life cycle dominated by crystalline mushes containing ephemeral, small (< 1 km3) segregations of melt. This interpretation helps to reconcile observations of high crustal electrical resistivity beneath Aluto, despite seismicity and ground deformation consistent with a magma body.

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

Cited by 30 publications

References 46 publications

Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

Phase Equilibria of Pantelleria Trachytes (Italy): Constraints on Pre-eruptive Conditions and on the Metaluminous to Peralkaline Transition in Silicic Magmas

Mixing and Crystal Scavenging in the Main Ethiopian Rift Revealed by Trace Element Systematics in Feldspars and Glasses

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