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Carbonate melts are characterized by exceptionally low viscosities compared to silicate melts, which greatly enhances their mobility. They play a crucial role in mantle metasomatism, carbonatite magma emplacement, degassing, some volcanic settings, and the global carbon cycle, making them a key component of planetary processes, although less abundant than silicate melts. As a result, understanding carbonate melt viscosity is essential for quantifying, modeling, and evaluating these fundamental processes.

Experimental studies on carbonate melt viscosities have been limited to specific compositions, high temperatures, and elevated pressures, making extrapolations within the carbonate system and across geologically relevant conditions challenging. The strongly non-Arrhenian viscosity-temperature relationship observed in carbonate melts, as demonstrated previously for the 55K₂CO₃-45MgCO₃ system by Dingwell et al. (2022), further impedes extrapolations to low temperatures.

To address this gap, we employed a novel approach combining pulsed laser deposition to produce glassy thin films with fast differential scanning calorimetry to measure the glass transition of CaCO₃ at extremely high heating and cooling rates (1,000–10,000 K/s). Using a factor that relates thermal to structural relaxation times, we derived viscosity values at these comparably low temperatures. Our results extend the explored viscosity range for CaCO₃ by seven orders of magnitude, positioning CaCO₃ as an alkaline-alkali endmember in the viscosity framework of carbonate melts.

Building upon our findings and published data, it is possible to estimate temperature dependent viscosities based on the alkali – alkaline ratio while considering the strongly non-Arrhenian behaviour. This provides a valuable tool for future studies, enabling more precise assessments of carbonate melt viscosity and mobility in diverse planetary settings.

Dingwell D. B., Hess K.-U., Wilding M. C., Brooker R. A., Di Genova D., Drewitt J. W. E., Wilson M. and Weidendorfer D. (2022) The glass transition and the non-Arrhenian viscosity of carbonate melts. American Mineralogist 107, 1053–1064.