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Viscosity data for dry and hydrous pantelleritic samples from Punta Spadillo (Pantelleria Island). GM = glass matrix; TR = total rock. Water content is measured by KFT. Temperature accuracy is +0.5 K for the low temperature data, and +1 K for the high temperature data. Viscosities are accurate to +0.05 log units based on DGG standard glass determinations.

Table 3 Viscosity data for dry and hydrous pantelleritic samples from Punta Spadillo (Pantelleria Island). GM = glass matrix; TR = total rock. Water content is measured by KFT. Temperature accuracy is +0.5 K for the low temperature data, and +1 K for the high temperature data. Viscosities are accurate to +0.05 log units based on DGG standard glass determinations.

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Fig. 1. Aerial photo of Pantelleria Island. Punta Spadillo sample location is shown with the Khaggiar lava flow (black area) belonging to Cuddia Randazzo center. The physical nature of peralkaline magmas also profoundly af- fects their processes of formation, eruption and emplacement. Peralkaline volcanic systems commonly exhibit substantial differ- ences in the physical nature of their eruptive prod ucts with respect to subalkaline centers. Examples are seen in the morphology of lava flows and in the nature and extent of vesiculation and welding of pyroclasts (Schmincke, 1974; Mahood and Hildreth, 1983, 1986; Rotolo et al., 2007; Gioncada and Landi, 2010). calcalkaline centers, which produce widespread In contrast with plinian deposits and ignimbrites, or basaltic volcanoes with more classic Hawaiian and Strombolian types of activity and spatter-fed eruptives, the The island of Pantelleria lies in the Sicily Channel, about 100 km from the SW coast of Sicily and only 70 km from Africa's northern coast, reaching a maximum elevation of 836 m above sea level. Pan- telleria Island is the type locality for the iron-rich peralkaline rhyolite named pantellerite by Forstner (1881). An extremely wide range of
Fig. 1. Aerial photo of Pantelleria Island. Punta Spadillo sample location is shown with the Khaggiar lava flow (black area) belonging to Cuddia Randazzo center. The physical nature of peralkaline magmas also profoundly af- fects their processes of formation, eruption and emplacement. Peralkaline volcanic systems commonly exhibit substantial differ- ences in the physical nature of their eruptive prod ucts with respect to subalkaline centers. Examples are seen in the morphology of lava flows and in the nature and extent of vesiculation and welding of pyroclasts (Schmincke, 1974; Mahood and Hildreth, 1983, 1986; Rotolo et al., 2007; Gioncada and Landi, 2010). calcalkaline centers, which produce widespread In contrast with plinian deposits and ignimbrites, or basaltic volcanoes with more classic Hawaiian and Strombolian types of activity and spatter-fed eruptives, the The island of Pantelleria lies in the Sicily Channel, about 100 km from the SW coast of Sicily and only 70 km from Africa's northern coast, reaching a maximum elevation of 836 m above sea level. Pan- telleria Island is the type locality for the iron-rich peralkaline rhyolite named pantellerite by Forstner (1881). An extremely wide range of
* Water content (wt.%) measured by infrared spectroscopy. > Water content (wt.%) measured by Karl-Fischer titration (KFT). © Water content (in mol%) considered for the parameterization. Measured water contents (FTIR and KFT), room temperature density (p) and iron spe- ciation of hydrated pantellerites.
* Water content (wt.%) measured by infrared spectroscopy. > Water content (wt.%) measured by Karl-Fischer titration (KFT). © Water content (in mol%) considered for the parameterization. Measured water contents (FTIR and KFT), room temperature density (p) and iron spe- ciation of hydrated pantellerites.
Dry composition (wt.%) of glasses. “ Al=agpaitic index (Na20 + K20)/Al203 1n mol. 6 PS-GM (glass matrix) and PS-TR (total rock): glasses of pantelleritic composition from Pantelleria Island from this study. © Glass compositions used for comparison purposes are also reported. FAN glass of pantelleritic composition from Fantale (Scarfe, 1977); 8 ka glass of pantelleritic compositior from Major Island (Stevenson et al., 1998); Td_ph glass of phonolitic composition from Teide (Giordano et al., 2000); VES_W glass of tephri-phonolitic composition from Vesuviu: (Romano et al., 2003); AMS_B1 glass of trachytic composition from Phlegrean Fields (Romano et al., 2003); VLC glass of shoshonitic composition from Vulcanello (Vetere et al., 2007); ETD glass of trachybasaltic composition from Etna (Giordano and Dingwell, 2003b); HPG8 synthetic glass of rhyolite composition (Dingwell et al., 1996); UNZ glass of dacitic composition fron Unzen (Giordano and Dingwell, 2003a); MNS glass of andesitic composition from Monserrat (Giordano et al., 2006); FR glass of latitic composition from Phlegrean Fields (Misiti et al. 2011); EIF glass of basanitic composition from Eifel (Giordano and Dingwell, 2003a); and VES glass of phono-tephritic composition from Vesuvius (Giordano et al., 2009). Table 1
Dry composition (wt.%) of glasses. “ Al=agpaitic index (Na20 + K20)/Al203 1n mol. 6 PS-GM (glass matrix) and PS-TR (total rock): glasses of pantelleritic composition from Pantelleria Island from this study. © Glass compositions used for comparison purposes are also reported. FAN glass of pantelleritic composition from Fantale (Scarfe, 1977); 8 ka glass of pantelleritic compositior from Major Island (Stevenson et al., 1998); Td_ph glass of phonolitic composition from Teide (Giordano et al., 2000); VES_W glass of tephri-phonolitic composition from Vesuviu: (Romano et al., 2003); AMS_B1 glass of trachytic composition from Phlegrean Fields (Romano et al., 2003); VLC glass of shoshonitic composition from Vulcanello (Vetere et al., 2007); ETD glass of trachybasaltic composition from Etna (Giordano and Dingwell, 2003b); HPG8 synthetic glass of rhyolite composition (Dingwell et al., 1996); UNZ glass of dacitic composition fron Unzen (Giordano and Dingwell, 2003a); MNS glass of andesitic composition from Monserrat (Giordano et al., 2006); FR glass of latitic composition from Phlegrean Fields (Misiti et al. 2011); EIF glass of basanitic composition from Eifel (Giordano and Dingwell, 2003a); and VES glass of phono-tephritic composition from Vesuvius (Giordano et al., 2009). Table 1
Fig. 2. Viscosities of total rock (PS-TR) and glass matrix (PS-GM) melts from Punte Spadillo (Pantelleria Island) at different water contents. Numbers in the legend are dissolved water contents (wt.% H20) measured by KFT.
Fig. 2. Viscosities of total rock (PS-TR) and glass matrix (PS-GM) melts from Punte Spadillo (Pantelleria Island) at different water contents. Numbers in the legend are dissolved water contents (wt.% H20) measured by KFT.
Fig. 3. Isokom temperatures (calculated at 10'° Pa s) variation as a function of H20 contents for Punta Spadillo total rock (PS-TR) and glass matrix (PS-GM) melts.
Fig. 3. Isokom temperatures (calculated at 10'° Pa s) variation as a function of H20 contents for Punta Spadillo total rock (PS-TR) and glass matrix (PS-GM) melts.
Fig. 4. Measured viscosities of pantelleritic samples of Punta Spadillo total rock PS-TR (a) and Punta Spadillo glass matrix PS-GM (b). Lines represent fitting according to Eqs. (3) and (5) (Table 5). Numbers in the legends indicate wt.% H20. (c) Comparison between measured and calculated viscosities from Eqs. (3) and (5) for both total rock and glass matrix samples. In order to extrapolate the viscosity variation outside the experi- mental range of our measurements and to compare our results with
Fig. 4. Measured viscosities of pantelleritic samples of Punta Spadillo total rock PS-TR (a) and Punta Spadillo glass matrix PS-GM (b). Lines represent fitting according to Eqs. (3) and (5) (Table 5). Numbers in the legends indicate wt.% H20. (c) Comparison between measured and calculated viscosities from Eqs. (3) and (5) for both total rock and glass matrix samples. In order to extrapolate the viscosity variation outside the experi- mental range of our measurements and to compare our results with
Chemical parameters of discussed compositions. * Non-bridging oxygen per tetrahedra on a molar basis (Mysen, 1988). > Sum of all structure modifier oxides on molar basis (mol%): FeO + MgO + CaO + Na,0 + K,0 + P205 + Mno. © Alkali excess on molar basis (mol%): NazO + K20-Al203. 4 Steepness index (e.g., Plazek and Ngai, 1991). Table 4
Chemical parameters of discussed compositions. * Non-bridging oxygen per tetrahedra on a molar basis (Mysen, 1988). > Sum of all structure modifier oxides on molar basis (mol%): FeO + MgO + CaO + Na,0 + K,0 + P205 + Mno. © Alkali excess on molar basis (mol%): NazO + K20-Al203. 4 Steepness index (e.g., Plazek and Ngai, 1991). Table 4
Fit parameters of experimental data according to Eqs. (3)-(5). Numbers in parentheses are standard deviations.
Fit parameters of experimental data according to Eqs. (3)-(5). Numbers in parentheses are standard deviations.
Fig. 6. Anhydrous viscosities versus reciprocal temperature for samples investigated in this study and literature data. (a): high T; (b) low T. NBO/T (number of non-bridging oxygen per tetrahedron), SM (i.e., the sum of all network modifier oxides (SM =Na20 + K,0 + CaO + MgO + MnO + FeO;o, Giordano and Dingwell, 2003a)). The chemical contribu- tion can be considered as related to all possible configurational states
Fig. 6. Anhydrous viscosities versus reciprocal temperature for samples investigated in this study and literature data. (a): high T; (b) low T. NBO/T (number of non-bridging oxygen per tetrahedron), SM (i.e., the sum of all network modifier oxides (SM =Na20 + K,0 + CaO + MgO + MnO + FeO;o, Giordano and Dingwell, 2003a)). The chemical contribu- tion can be considered as related to all possible configurational states
Fig. 5. TAS (total alkali vs. SiO2 contents in wt.%) diagram showing melt compositions from this study and from literature.
Fig. 5. TAS (total alkali vs. SiO2 contents in wt.%) diagram showing melt compositions from this study and from literature.
Fig. 7. Isokom temperature variation as a function of wt.% H20 at 10'° Pa s calculated through Arrhenian fits of low temperature experimental data. where M is a network modifying cation. The effect of forming free OH™ would be to polymerize the silicate network, by also creating bridging oxygens. The net effect of water dissolution would depend on the rela- tive abundance of free OH~ species over SiOH and AIOH species (Giordano et al., 2009). In principle, all three mechanisms can operate simultaneously, but the polymerization reaction alone would lead to an increase in viscosity with the addition of water, which has never
Fig. 7. Isokom temperature variation as a function of wt.% H20 at 10'° Pa s calculated through Arrhenian fits of low temperature experimental data. where M is a network modifying cation. The effect of forming free OH™ would be to polymerize the silicate network, by also creating bridging oxygens. The net effect of water dissolution would depend on the rela- tive abundance of free OH~ species over SiOH and AIOH species (Giordano et al., 2009). In principle, all three mechanisms can operate simultaneously, but the polymerization reaction alone would lead to an increase in viscosity with the addition of water, which has never
Fig. 8. Comparison between measured and calculated viscosities from (a) Giordano et al. (2008b) to (b) Hui and Zhang (2007).
Fig. 8. Comparison between measured and calculated viscosities from (a) Giordano et al. (2008b) to (b) Hui and Zhang (2007).
Fit parameters for Eq. (8). Numbers in parentheses are standard deviations.
Fit parameters for Eq. (8). Numbers in parentheses are standard deviations.
Fig. 9. Comparison between measured and calculated viscosities from Eqs. (3) to (8) for pantelleritic melts studied in this work and data provided by Scarfe, 1977 (FAN) and Stevenson et al., 1998 (8 ka) for pantellerites.
Fig. 9. Comparison between measured and calculated viscosities from Eqs. (3) to (8) for pantelleritic melts studied in this work and data provided by Scarfe, 1977 (FAN) and Stevenson et al., 1998 (8 ka) for pantellerites.
Fig. 11. Effect of crystal content on liquid viscosity as a function of temperature (a) anc water content (b). Comparison with literature data reveals a strong influence of the alkali content on the overall viscosity of the melt. In the high temper- ature regime, pantelleritic samples exhibit viscosities intermediate between andesitic and phonolitic melts, and more than 2 orders of
Fig. 11. Effect of crystal content on liquid viscosity as a function of temperature (a) anc water content (b). Comparison with literature data reveals a strong influence of the alkali content on the overall viscosity of the melt. In the high temper- ature regime, pantelleritic samples exhibit viscosities intermediate between andesitic and phonolitic melts, and more than 2 orders of
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