High-temperature apparatus for chaotic mixing of natural silicate melts

Abstract:

A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term ChaOtic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10⁶ Pas) natural silicate melts. The instrument represents an extraordinary advance because allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges in the volcanic environment. The COMMA device is tested at extreme conditions by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1170°C, with melts of shoshonitic and rhyolitic composition, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. We anticipate the COMMA to become a state-of-the-art apparatus for detailed investigations of magma mixing processes providing unprecedented information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.