Publication Date:
2021-01-14
Description:
Viscosities of shoshonitic and latitic melts, relevant to the Campi Flegrei caldera
magmas, have been experimentally determined at atmospheric pressure and 0.5 GPa,
temperatures between 840 K and 1870 K, and H2O contents from 0.02 to 3.30 wt%.
The concentric cylinder technique was employed at atmospheric pressure to determine
viscosity of nominally anhydrous melts in the viscosity range of 101.5 - 103 Pa·s. The
micropenetration technique was used to determine the viscosity of hydrous and anhydrous
melts at atmospheric pressure in the high viscosity range (1010 Pa·s). Falling sphere
experiments were performed at 0.5 GPa in the low viscosity range (from 100.35 to 102.79 Pa·s)
in order to obtain viscosity data of anhydrous and hydrous melts. The combination of data
obtained from the three different techniques adopted permits a general description of viscosity
as a function of temperature and water content using the following modified VFT equation:
where η is the viscosity in Pa·s, T the temperature in K, w the H2O content in wt%, and a, b, c,
d, e, g are the VFT parameters. This model reproduces the experimental data (95
measurements) with a 1σ standard deviation of 0.19 and 0.22 log units for shoshonite and
latite, respectively. The proposed model has been applied also to a more evolved composition
(trachyte) from the same area in order to create a general model applicable to the whole
compositional range of Campi Flegrei products.
Moreover, speed data have been used to constrain the ascent velocity of latitic,
shoshonitic, and trachytic melts within dikes. Using petrological data and volcanological
information (geometrical parameters of the eruptive fissure and depth of magma storage), we
estimate a time scale for the ascent of melt from 9 km to 4 km depth (where deep and shallow
reservoirs, respectively, are located) in the order of few minutes. Such a rapid ascent should
be taken into account for the hazard assessment in the Campi Flegrei area.
Description:
Published
Description:
50-59
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
open
Keywords:
viscosity
;
micropenetration
;
concentric cylinder
;
falling sphere
;
shoshonites
;
latites
;
Campi Flegrei
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
