The wondrous world of element partitioning, with excursions to ore deposits, subduction zones and the origins of life

The abundance of water in and on the Earth has a profound impact on the processes that shape our planet, from allowing plate tectonics to operate, to concentrating elements to form ore deposits, to facilitating magmatism. Moreover, water is the likely medium in which life originated, and the early evolution of organisms is tightly linked to the compositional evolution of its host fluid. In order to understand the impacts of water, it is necessary to know the compositions of these fluids, in particular their trace element contents. At present, such information is severely lacking, because direct fluid samples are rare and their chemical characterization non-trivial. In this presentation I will propose a different approach in which the composition of the fluid is reconstructed from that of associated minerals, based on the characteristic trace element partitioning between minerals and aqueous fluids. Unlike fluids, minerals with preserved compositions are readily available in the geological record, and this approach therefore provides a powerful and widely applicable tool to reconstruct fluid compositions for the full range of Earth environments and back to the earliest history of our planet.