![]() ![]() With respect to the synthetic simplified tholeiitic composition used by Sakamaki et al. Among the diverse suite of basalts, the primitive magma at Campi Flegrei is of interest as it shows geochemical and petrological evidences of a mantle source that might still feed the current pre-eruptive system 13, 14 and lead to dramatic eruptions. ![]() We experimentally determined the viscosity of a primitive alkali basalt composition at pressures (P) representative of upper mantle to reveal the effect of its mobility and ascent velocity on the timing of magmatic supply of deep portions of volcanic plumbing systems where, in absence of faults and dikes, the magma moves by porous flow. Although such studies highlighted differences in viscosity up to four orders of magnitude within ~ 1.5–13.0 GPa and temperatures up to ~ 2200 ☌ for melts that have SiO 2 contents between 46.6 and 67.5 wt% 12, at present none of these compositions can be taken as unique reference values to model the rheological behavior of mantle-derived subduction-related basalts. ![]() More recent experimental studies have used in-situ X-ray radiography techniques combined with high-pressure apparatus, which have allowed to explore a wide range of simplified silicate melt compositions like peridotitic 7, basaltic 8, trachy-andesitic 9, albitic 10 and dacitic 11 melts at high pressure and temperature representative of Earth’s mantle regions. These models cannot be used to predict viscosity at mantle depths where primitive magmas originate and, therefore, the effect of pressure is such to influence their atomic structure 6. These viscosity models can be safely used to model the viscosity at atmospheric conditions (e.g., lava emplacement) or for shallow magma bodies or conduits where the effect of pressure can be considered negligible. Additional studies have provided empirical numerical models to determine the viscosity of melt compositions spanning terrestrial volcanic rocks from basic to silicic, from subalkaline to peralkaline, and from metaluminous to peraluminous 5 (and references therein). Several studies have investigated the viscosity of natural 1, 2 and synthetic magmas at various pressure conditions from atmospheric to ~ 400 MPa 3, 4. Understanding the rheological properties of magmas at pressures and temperature at which they form is necessary to model the ascent rate from Earth’s mantle up to the surface. ![]()
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