Ricerc@Sapienza

This project will focus on the geochemical evolution of olivine from primitive skarn environments. Magma-carbonate interaction will be investigated by a vertical tube CO¿CO2 gas-mixing furnace. Atmospheric pressure experiments will be carried out at 1250, 1200, and 1150 °C under QFM buffer. The starting materials will be three synthetic basalts (i.e., meltMg#78, meltMg#75, and meltMg#72) doped with variable amounts of CaCO3, in order to reproduce the natural concentration levels of CaO-rich magmas interacting with the skarn rock shells. Results from decarbonation experiments will evidence as the crystallization of MgO-CaO-rich, NiO-poor olivines can be potentially more favored at high temperature, when primitive basaltic magmas assimilate increasing amounts of carbonate materials. This will provide important constrains on the partitioning behavior of major and trace elements and on the formation of ore deposits hosted by skarn environments. In fact, the number of large size Ca cations entering olivine crystal lattice is known to be proportional to the amount of Ca-O-Si bonds available in the melt. Due to differences between Fe2+ and Mg cation radii, the Ca-Fe2+ substitutions into M2 crystallographic site will be more facilitated than Ca-Mg ones, thus enhancing the MgO in olivine. The partitioning behavior of trace elements between olivine and decarbonated melts will be investigated to quantify cation redistribution mechanisms at the magma-carbonate reaction zone. Under the effect of CaCO3 assimilation, the partitioning of divalent and trivalent cations will be parameterized as a function of temperature, bulk composition (CaO and MgO) and melt structure (NBO/T). I will also investigate as cation exchange reactions can be controlled by the strong depolymerizing effect of CaCO3 assimilation that, in turn, is expected to increase the number of structural sites critically important to accumulate rare and precious cations in the melt phase.