Viscosity measurements of crystallizing andesite from T ungurahua volcano ( E cuador)

Abstract

Viscosity has been determined during isothermal crystallization of an andesite from Tungurahua volcano (Ecuador). Viscosity was continuously recorded using the concentric cylinder method and employing a Pt‐sheathed alumina spindle at 1 bar and from 1400°C to subliquidus temperatures to track rheological changes during crystallization. The disposable spindle was not extracted from the sample but rather left in the sample during quenching thus preserving an undisturbed textural configuration of the crystals. The inspection of products quenched during the crystallization process reveals evidence for heterogeneous crystal nucleation at the spindle and near the crucible wall, as well as crystal alignment in the flow field. At the end of the crystallization, defined when viscosity is constant, plagioclase is homogeneously distributed throughout the crucible (with the single exception of experiment performed at the lowest temperature). In this experiments, the crystallization kinetics appear to be strongly affected by the stirring conditions of the viscosity determinations. A TTT (Time‐Temperature‐Transformation) diagram illustrating the crystallization “nose” for this andesite under stirring conditions and at ambient pressure has been constructed. We further note that at a given crystal content and distribution, the high aspect ratio of the acicular plagioclase yields a shear‐thinning rheology at crystal contents as low as 13 vol %, and that the relative viscosity is higher than predicted from existing viscosity models. These viscosity experiments hold the potential for delivering insights into the relative influences of the cooling path, undercooling, and deformation on crystallization kinetics and resultant crystal morphologies, as well as their impact on magmatic viscosity.

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

“…Interestingly, the transition from Newtonian to non-Newtonian flow has also been reported in subliquidus magmas [45][46][47]49,115,116]. Of particular relevance is the observation that shear-thinning tendency increases with solid phase content, and that the increase in viscosity is attributable mainly to the solid phase formation [45].…”

Constraining pre-eruptive magma conditions and unrest timescales during the Monte Nuovo eruption (1538 ad; Campi Flegrei, Southern Italy): integrating textural and CSD results from experimental and natural trachy-phonolites

“…Time-temperature-transformation (TTT) diagrams (Fig. 10a) are useful for showing the effect of undercooling and viscosity on transformation kinetics (Kouchi et al 1986;Putnis 1992;Porter and Easterling 1997;Hammer and Rutherford 2002;Chevrel et al 2015). The TTT plot for the crystal fraction variations was determined from the results of the isothermal decompression experiments as a function of ΔT, P f and time (Fig.…”

Magma mixing enhanced by bubble segregation

“…The quench rate is estimated to range around few degrees per second, similar to studies using comparable procedures (e.g. Chevrel et al, 2015). The post-experimental glassy assemblage was cored from the crucible to yield a sample cylinder of 20 mm diameter.…”