The finding of metamorphic coesite and microdiamonds in gneisses completely changed the ideas of geologists concerning subduction of continental crust. These minerals provide evidence that crustal rocks were subducted up to 130 km depth and later exhumed to Earth's surface. Because of the scarcity of experimental data for felsic crustal rocks in diamond-facies conditions, up to now proof of diamond-facies metamorphism is restricted to rocks actually containing microdiamonds. In the proposed project new thermobarometers for crustal ultra-high pressure (UHP) rocks will be tested and developed using the main UHP mineral assemblage garnet-phengite-kyanite-clinopyroxene-coesite-rutile-zircon-apatite. The project includes experimental petrology, detail chemical characterisation of experiments and natural rocks and thermodynamic analysis.

In this project we propose an interdisciplinary approach to develop new and innovative tools for high-resolution investigation of partial melting and high-grade metamorphism. These tools are based on recent findings that trace elements, due to their slower diffusion, are the most retentive record of metamorphic processes. The stability of accessory phases, which are commonly the major hosts of trace elements, will be studied in natural rocks and experiments, particularly to investigate the potential of such phases to buffer trace element contents of partial melts. The project includes experimental petrology, detail chemical characterisation of experiments and natural rocks and analysis of trace element partitioning.