The composition and abundance of the volcanic gases has strongly influenced the habitability of our planet over time. The Earth's mantle represents the largest reservoir of elements like carbon, hydrogen, boron, nitrogen and sulfur, but their residence time in depth and their release to the atmosphere strongly depend on pressure (P), temperature (T) and oxygen fugacity (fo2) at which they are transferred from host minerals to magmas affecting, in turn, their viscosity, density and eruptive styles at the surface. Only once magmas rise up to the surface, volatile elements become less soluble and start to degas to the atmosphere or transferred to shallow waters, e.g. oceans and groundwaters. To be able to model the cycle of volatile elements from the mantle to the atmosphere, we need to know the ascent rate of magmas as function of their composition, pressure and temperature; this links with the rheological properties of magmas, i.e. viscosity and melt structure. In addition, elements like C, H2O and B are all soluble into terrestrial magmas and might affect the physical properties of melts. However, as these elements are incorporated in minerals (C in diamonds, graphite and carbonates; H2O and B in tourmaline, H2O in amphiboles but also nominally anhydrous minerals), it is necessary to understand what mechanism controls their partition to melts (e.g. redox reactions, decomposition, dissolution).
Therefore, the aim of this project is,
1) To investigate the pressure, temperature and oxygen fugacity at which C, H and B are transferred from typical host minerals of the Earth' s interior to coexisting magmas;
2) to determine the physical properties (viscosity and melt structure) of C-, H2O- and B-rich liquids representative of terrestrial magmas and (metasomatic) fluids at pressures and temperatures of the Earth' s upper mantle;
3) to measure the dissolution rate of minerals and melts when in contact with water with particular focus for the partition of C and B.
The novelty of our research is described the Step 4.
The obtained viscosity data from synthetic melts along with models of density, rock permeability and porosity allow to make estimates of the ascent time of volatile-bearing terrestrial magmas from the rock source to the surface. On the other hand, the rheology of magmas is what controls the eruption style on the surface especially in the case of volcanoes the activity of which is nowadays controls by mantle-derived magma blobs (e.g. Campi Flegrei and Etna). Rheological information supported by data on the solubility of volatiles in magmas as function of P and T make us able to calculate the volatile budget released to the atmosphere over time. Additionally, we mentioned the possibility to equilibrate tourmaline (chosen as source of B) and melts and measure the concentration of B in both. This implies the potential use of natural tourmalines from various localities (e.g., Italy, Canada, Kazakhstan, Australia, Norwegian and USA) as indicator of magma-forming petrogenetic processes. In this regard, the possibility to identify new tourmaline species will provide useful information for application of thermodynamics and petrology. Finally, the dissolution of glasses with different compositions in water is needed to model the preservation of the geochemical signature of natural lavas and interpret chemical anomalies of groundwaters in contact with volcanic edifices to be used as precursor of volcanic activity.
These are important outcomes from this project that would emphasize the importance of using a multidisciplinary approach to the study of the physics of amorphous and crystalline substances.