PhD Student Manolis Giampouras defended his thesis

In continental settings, the interaction between meteoric water and ultramafic rocks generates waters of variable physicochemical characteristics due to serpentinization and weathering. The discharge of these waters forms aerial alkaline to hyperalkaline spring systems where waters mix, undergo evaporation, and take up atmospheric CO2, leading to the precipitation of carbonate minerals. The understanding of natural carbonation in these serpentinite-hosted alkaline environments is critical, among others, for assessing the role of this process in the global carbon cycle throughout the Earth’s history, and the viability of CO2 sequestration techniques for permanent carbon storage.

The main objective of the PhD thesis is to advance in our understanding of serpentinization-related alkaline spring systems and the precipitation of calcium carbonate minerals in these alkaline environments. To attain this goal, this thesis investigates the factors controlling carbon mineralization in two natural case studies of active alkaline spring systems hosted in serpentinized peridotites in oceanic (Samail Ophiolite, Oman) and subcontinental mantle (Ronda peridotites, Spain) tectonically emplaced in continental orogens. The detailed study of the chemical composition of alkaline waters, along with the mineralogy and textures of precipitates, allows to unveil the geochemical and mineralogical characteristics of these alkaline springs and evaluate how the interaction of hyperalkaline fluids with surface waters and the atmosphere affects carbonate precipitation. Furthermore, the thesis presents new results of crystallization experiments aimed at constraining the nucleation, crystal growth, and transformation conditions and the mechanisms of formation of hydrated Mg-carbonates in alkaline environments. By combining the study of active alkaline spring systems and experimental work, the present PhD thesis contributes to filling gaps in our current knowledge on the mechanisms and conditions of carbonate precipitation in alkaline environments.

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