Variation in Mineralogy, Temperature, and Oxygen Fugacity in a Suite of Strongly Peralkaline Lavas and Tuffs, Pantelleria, Italy

White, John C.; Ren, Minghua; Parker, Don F.

doi:10.2113/gscanmin.43.4.1331

Cited by 66 publications

(89 citation statements)

References 61 publications

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“…This is in accord with the general situation in peralkaline rhyolites; hedenbergite is the normal pyroxene phenocryst even in the most strongly peralkaline rocks, aegirine-augite being recorded only rarely (Macdonald et al 2011). This is probably related to the relatively low fO 2 at which the magmas evolve, at or close to FMQ (Scaillet and Macdonald 2001White et al 2005White et al , 2009Ren et al 2006;Di Carlo et al 2010). A microphenocryst in B355 has a relatively magnesian core (Ca 44.9 Mg 21.1 Fe 34.0 ), which may represent a highertemperature phase of magmatic evolution or mixing of the pantellerite with a more trachytic magma.…”

Section: Olivinesupporting

confidence: 86%

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Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

et al. 2011

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Matrix glass and melt inclusions in phenocrysts from pantellerite lavas of the Boseti volcanic complex, Ethiopia, record extreme fractionation of peralkaline silicic magma, with Al 2 O 3 contents as low as 2.3 wt.%, FeO* contents up to 17 wt.% and SiO 2 contents~65 wt.%. The new data, and published data for natural and experimental glasses, suggest that the effective minimum composition for peralkaline silicic magmas has~5 wt.% Al 2 O 3 , 13 wt.% FeO* and 66±2 wt.% SiO 2 . The dominant fractionating assemblage is alkali feldspar + fayalite + hedenbergite + oxides±quartz. Feldspar -melt relationships indicate that the feldspar is close to the minimum on the albiteorthoclase solid solution loop through the entire crystallization history. There is petrographic, mineralogical and geochemical evidence that magma mixing may have been a common process in the Boseti rhyolites.

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Section: Olivinesupporting

confidence: 86%

“…Semi-quantitative analyses indicate, however, that it is pyrrhotite, which has also been recorded as microphenocrysts in peralkaline rhyolites from Tejeda volcano, Gran Canaria (Crisp and Spera 1987), Pantelleria (Lowenstern et al 1993;White et al 2005) and Eburru, Kenya (Ren et al 2006).…”

Section: Sulphidementioning

confidence: 99%

Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

et al. 2011

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“…Mattia et al, 2007). The range of temperature investigated (680^8008C) encompasses that inferred by White et al (2005) for the felsic end-members, but also reflects the conditions required to match the crystal-poor condition characterizing most Pantelleria rhyolites, including the selected starting material, and the variation of this parameter with H 2 O melt .The starting material (PAN 01113) belongs to the Fastuca pumice fall eruptive unit (Orsi et al, 1989) and was sampled from the bottom portion of the deposit, which consists of dense, variably welded, pumice that has locally agglutinated to produce vitrophyric bands. Welding and agglutination to form thin, lava-like layers is common at Pantelleria in pumice-fall deposits located close to the vents (Rotolo et al, 2007).…”

mentioning

confidence: 79%

“…They did not consider the physical conditions under which magmatic differentiation occurs, such as the temperature of crystal^melt equilibration, or the melt viscosity and density, which heavily depend on temperature and volatile contents. This gap has been partly filled with the detailed petrological studies of White et al (2005White et al ( , 2009, who used thermobarometric tools (e.g. QUILF) and the MELTS solution model to work out the intensive parameters for the Pantelleria magmatic suite.…”

Section: Geological and Petrological Backgroundmentioning

confidence: 99%

Phase Equilibrium Constraints on Pre-eruptive Conditions of Recent Felsic Explosive Volcanism at Pantelleria Island, Italy

Carlo

Rotolo

Scaillet

et al. 2010

Journal of Petrology

130

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We present experimental phase equilibria carried out on a pantelleritic bulk-rock composition with a peralkalinity index [PI INTRODUCTIONPantelleria island is the type-locality of pantellerite, an iron-and sodium-rich peralkaline rhyolite. Pantellerites, by far the most abundant rock-type at Pantelleria, occur as pyroclastic flows, pumice fall deposits, or as obsidianaceous lavas (Mahood & Hildreth, 1986). After the Plinian eruption of the Green Tuff (45 ka BP), and the related caldera collapse, resurgent felsic magmatism was mainly centered inside the caldera, producing either low-energy explosive eruptions or lava flows.Recent experimental investigations (Scaillet & Macdonald, 2001 and melt inclusion studies (Kovalenko et al., 1988;Webster et al., 1993;Wilding et al Barclay et al., 1996;Gioncada & Landi, 2010) have shown that peralkaline melts may be rather H 2 O-rich, in contrast to previous inferences. These studies have also demonstrated the role of pressure, water, oxygen fugacity, and silica and sodium disilicate activity (aSiO 2 , aNds) on the phase equilibria of felsic peralkaline magmas from the east Kenyan rift zone (e.g. Scaillet & Macdonald, 2001Caricchi et al., 2006). In this study we present the hydrous phase equilibria of a pantellerite with a peralkalinity index PI [ ¼ molar (Na 2 O þ K 2 O)/Al 2 O 3 ] ¼ 1·4, established within the pressure range 25^150 MPa, for temperatures between 680 and 8008C, with oxygen fugacities below the Ni^NiO solid buffer (NNO), and melt water contents (H 2 O melt ) up to 6 wt %. We apply our experimentally derived P^TĤ 2 O melt grid to natural pantellerites to assess the pre-eruptive conditions (T, P,H 2 O melt )ofthemostpowerful event of the post-caldera period, the Fastuca eruption (Orsi et al.,1989). Knowledge of the pre-eruptive conditions sheds light on the nature of the magmatic plumbing system associated with recent felsic volcanism at Pantelleria, with several obvious implications for the eruptive style of pantellerite magmas. The determination of magma storage conditions of pantelleritic magmas can also provide constraints on the more general problem of the origin of silica-oversaturated peralkaline magmas, which has been extensively debated (see Bohrson & Reid, 1997;Civetta et al., 1998;Marshall et al., 1998;Marshall et al. 2009;Scaillet & Macdonald, 2001;Nekvasil et al., 2004;Macdonald et al., 2008). Much of the controversy has arisen because of the lack of modern phase equilibrium constraints for peralkaline magmas, in contrast to their metaluminous or peraluminous counterparts (e.g. Dall' Agnol et al., 1999;Klimm et al., 2003;Bogaerts et al., 2006). GEOLOGICAL AND PETROLOGICAL BACKGROUNDPantelleria (Italy) is an entirely volcanic island ( Fig. 1) located within the Sicily Channel continental rift system, in the northern part of the African plate (e.g. Rotolo et al., 2006). Pantelleria is well known in the petrological literature because its eruptive products represent a typical bimodal suite: a mafic end-member, which consists of mildly alkali basalts, a...

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“…The crystallization of Na-rich clinopyroxene (i.e., aegirine-augite and aegirine) and other Na-bearing phases, such as arfvedsonite, contribute efficaciously to the formation of peralkaline magmas (White et al 2005). The stability and composition of clinopyroxene and arfvedsonite are temperature-, H 2 O activity-, melt composition-and fO 2 -dependent (Scaillet and Macdonald 2001).…”

Section: Inferences Concerning Conditions Of Crystallizationmentioning

confidence: 99%

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

Mbowou¹,

Lagmet²,

Nomade³

et al. 2012

J. Geosci.

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Late Cretaceous peralkaline rhyolites (69.4 ± 0.4 Ma -2σ analytical, 1.9 Ma full external uncertainty, 40 Ar/ 39Ar sanidine single crystal laser dating) from Lake Chad are the oldest lavas of the "Cameroon Hot Line". These lavas (pantellerite and comendite), consisting of quartz ± alkali feldspar ± fluoro-arfvedsonite ± augite-hedenbergite ± aegirine ± fayalite (Fa 97-99 ) and ilmenite, are characterized by a progressive increase in the total REE contents and the magnitude of the negative Eu anomaly owing to the alkali feldspar-dominated fractionation. Two groups of peralkaline rhyolites have been distinguished according to mineralogical and geochemical data. Both, group-1 (La N /Yb N : 8.4-9.0; Zr/Nb: ~ 8) and group-2 (La N /Yb N : 10.7-12.6; Zr/Nb: ~ 6) are genetically related. The peralkaline rhyolites from Lake Chad could not be solely the product of fractional crystallization from a basaltic parental magma. The influx of F-rich fluids could have greatly modified the composition of rhyolitic magmas as attested by the presence of fluoro-arfvedsonite.

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Variation in Mineralogy, Temperature, and Oxygen Fugacity in a Suite of Strongly Peralkaline Lavas and Tuffs, Pantelleria, Italy

Cited by 66 publications

References 61 publications

Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

Phase Equilibrium Constraints on Pre-eruptive Conditions of Recent Felsic Explosive Volcanism at Pantelleria Island, Italy

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

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