Viscosity of pantelleritic and alkali-silicate melts: Effect of Fe redox state and Na/(Na + K) ratio

Stabile, Paola; Webb, Sharon L.; Knipping, Jaayke L.; Behrens, Harald; Paris, Eleonora; Giuli, Gabriele

doi:10.1016/j.chemgeo.2016.09.003

Cited by 23 publications

(16 citation statements)

References 60 publications

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“…These compositional characteristics are responsible for the low viscosity of our silicate melt. Previous experimental data [e.g., Le Losq and Neuville , ; Vetere et al , ; Stabile et al , ] are in agreement with the lower melt viscosity described here.…”

Section: Resultssupporting

confidence: 92%

Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

et al. 2017

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We present new viscosity measurements of a synthetic silicate system considered an analogue for the lava erupted on the surface of Mercury. In particular, we focus on the northern volcanic plains (NVP), which correspond to the largest lava flows on Mercury and possibly in the Solar System. High‐temperature viscosity measurements were performed at both superliquidus (up to 1736 K) and subliquidus conditions (1569–1502 K) to constrain the viscosity variations as a function of crystallinity (from 0 to 28%) and shear rate (from 0.1 to 5 s−1). Melt viscosity shows moderate variations (4–16 Pa s) in the temperature range of 1736–1600 K. Experiments performed below the liquidus temperature show an increase in viscosity as shear rate decreases from 5 to 0.1 s−1, resulting in a shear thinning behavior, with a decrease in viscosity of ~1 log unit. The low viscosity of the studied composition may explain the ability of NVP lavas to cover long distances, on the order of hundreds of kilometers in a turbulent flow regime. Using our experimental data we estimate that lava flows with thickness of 1, 5, and 10 m are likely to have velocities of 4.8, 6.5, and 7.2 m/s, respectively, on a 5° ground slope. Numerical modeling incorporating both the heat loss of the lavas and its possible crystallization during emplacement allows us to infer that high effusion rates (>10,000 m3/s) are necessary to cover the large distances indicated by satellite data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft.

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Section: Resultssupporting

confidence: 92%

Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

et al. 2017

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“…Notably, the viscosity of peralkaline rhyolites is relatively low compared with that of calc-alkaline rhyolites. This is due to their alkali-rich compositions that depolymerize the melt structure (Stevenson et al, 1998;Mysen, 2007;Mysen and Toplis, 2007;Di Genova et al, 2013;Stabile et al, 2016). Although hydrous peralkaline rhyolites with concentration of H 2 O ≤ 4 wt.% have relatively low viscosities (10 2 to 10 5 Pa s; Di Genova et al, 2013), their volcanic activity is characterized by a wide range of eruptive styles.…”

Section: Introductionmentioning

confidence: 99%

Crystallization Kinetics of Alkali Feldspar in Peralkaline Rhyolitic Melts: Implications for Pantelleria Volcano

et al. 2020

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Peralkaline rhyolites, associated with extensional tectonic settings, are medium to low viscosity magmas that often produce eruptive styles ranging from effusive to highly explosive eruptions. The role of pre-eruptive conditions and crystallization kinetics in influencing the eruptive style of peralkaline rhyolitic magmas has been investigated and debated considering equilibrium conditions. However, experimental constraints on the effect of disequilibrium in crystallization in such magmas are currently lacking in the literature. Therefore, we performed isobaric cooling experiments to investigate alkali feldspar crystallization kinetics in peralkaline rhyolitic melts. Experiments were performed under water-saturated, water-undersaturated, and anhydrous conditions between 25 and 100 MPa, at 670-790 • C and with experimental durations ranging from 0.5 to 420 h. Here we present the first data on crystallization kinetics of alkali feldspar, which is the main crystal phase in peralkaline rhyolitic melts, in order to improve our understanding of the evolutionary timescales of these melts and their ability to shift between effusive and explosive activity. Our experimental results indicate that the alkali feldspar nucleation delay can range from hours to several days as a function of undercooling and H 2 O content in the melt. Thus, a peralkaline rhyolitic magma can be stored at the pre-eruptive conditions for days without important variations of its crystal fraction. This suggests that crystallization may not necessarily play the main role in triggering fragmentation during explosive eruptions of peralkaline rhyolitic magmas.

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“…However, given the low viscosity of pantelleritic liquids [Neave et al, 2012], there should be other mechanisms, which trigger the most explosive style. Previous studies have demonstrated that these peralkaline rhyolites, at low temperatures, have lower viscosity than metaluminous rhyolites due to the effect of alkalis that strongly depolymerize the melt, decreasing their configurational entropy and the viscosity [Di Genova et al, 2013, Stabile et al, 2016.…”

Section: Pantelleria Volcanic Systemmentioning

confidence: 99%

“…Peralkaline rhyolites have lower viscosity than calcalkaline rhyolites due to the high alkali content that strongly depolymerizes the melt structure [Stevenson et al, 1998, Mysen, 2007, Mysen and Toplis, 2007, Di Genova et al, 2013, Stabile et al, 2016, and they can shift between explosive and effusive eruptive behaviour, thus producing a wide variety of eruptive styles, ranging from lava flows and fountains to Strombolian to sub-Plinian and Plinian eruptions [e.g., Schmincke, 1974, Mahood and Hildreth, 1986, Duffield, 1990, Lowestern and Mahood, 1991, Houghton et al, 1992, Stevenson et al, 1993, Webster et al, 1993, Wilding et al, 1993, Barclay et al, 1996, Stevenson and Wilson, 1997, Horn and Smincke, 2000, Gottsmann and Dingwell, 2002. Although peralkaline rhyolites were once thought to be relatively H 2 O poor [Bailey and MacDonald, 1987], more recent studies indicate magma water contents as high as 5-6 wt% H 2 O [e.g., Kovalenko et al, 1988, Webster et al, 1993, Wilding et al, 1993, Barclay et al, 1996, Gioncada and Landi, 2010, Di Carlo et al, 2010, Lanzo et al, 2013, Romano et al, 2019.…”

Section: Introductionmentioning

confidence: 99%

Crystallization of peralkaline rhyolitic magmas: pre- and syn-eruptive conditions of the Pantelleria system

Stabile¹,

Arzilli²,

Carroll³

2022

Comptes Rendus. Géoscience

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Pantelleritic magmas are low-viscosity peralkaline rhyolites which exhibit large differences in eruptive style (explosive to effusive). The processes that promote fragmentation and explosive eruptions of pantelleritic magma remain subject to debate, but undoubtedly variations of magma viscosity during magma ascent and degassing contribute to differences in eruptive style. Because crystallization can significantly influence magma rheology, we present a review of equilibrium and disequilibrium crystallization experiments of pantellerites, focusing on the crystallization of the main phases, alkali feldspar, and (lesser) clinopyroxene. Our analysis of data for several explosive pantelleritic eruptions on Pantelleria suggests pre-eruptive pressures of 50-100 MPa, temperatures of 700-800°C for water-saturated conditions. Given these conditions, we show that the low pre-eruptive crystal fractions (0.08 to 0.15), temperatures between 700 and 800°C, and the decrease of melt H 2 O content during magma ascent/decompression can promote a significant change in viscosity (up to 10 6 -10 7 Pa•s), leading to magma brittle fragmentation and explosive eruptions. Because of their typical range of viscosity, pantelleritic magmas may show greater variations in eruptive style due to differences in ascent (decompression) rate when compared with metaluminous rhyolites.

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Viscosity of pantelleritic and alkali-silicate melts: Effect of Fe redox state and Na/(Na + K) ratio

Cited by 23 publications

References 60 publications

Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

Experimental constraints on the rheology, eruption, and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains

Crystallization Kinetics of Alkali Feldspar in Peralkaline Rhyolitic Melts: Implications for Pantelleria Volcano

Crystallization of peralkaline rhyolitic magmas: pre- and syn-eruptive conditions of the Pantelleria system

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