The deep water cycle
Water has a profound influence on how Earth operates. It has been suggested that plate tectonics as it operates on Earth is only possible if small amounts of water are present in the Earth’s interior. In spite of the fundamental importance of water carried deep into the Earth in controlling the evolution of our planet, there are still many open questions.
We are investigating how water is transferred in subduction zones from hydrous minerals, which are generally stable only to about 100 km depth, to nominally anhydrous minerals that are able to carry water to the deeper mantle. We use a wide variety of mafic and ultramafic rocks from well-characterised areas in the Alps as a natural laboratory to study this process. We aim to investigate how and how much water is incorporated during progressive dehydration reactions into olivine, garnet, pyroxene and rutile as a function of pressure, temperature and composition. These results will be compared to water incorporation in lithospheric mantle sections that were undersaturated in water. Special emphasis will be placed on investigating whether the nominally anhydrous minerals lost or gained water by diffusion during their journey back to the surface by comparing natural samples with experimental results. If water diffusion is observed, we will evaluate the potential of such diffusion profiles to obtain information on the duration of metamorphic processes at moderate temperatures.
The studies on how water is subducted will be complemented by research on how water is lost from the mantle through volcanism. We will develop new methods to efficiently analyse melt inclusions hosted in pyroxene and olivine phenocrysts in primitive lavas by FTIR spectroscopy. Protocols for water measurements in geological materials must be established for the new infrared spectroscopy laboratory in Bern and the SwissSIMS in Lausanne.