One of the fundamental tasks of Geosciences is to elucidate the transport and transformation of material through the various reservoirs of the dynamic, evolving Earth system. Of particular interest is an understanding of the processes at active plate margins, which include transport of fluids, melts and solid materials. The most important global geomaterial cycles are connected with material fluxes at mid-ocean ridges and subduction zones. The interaction of solid geomaterial with melts and fluids in these tectonic environments are the primary mechanisms for material exchange between the deep Earth, lithosphere, hydrosphere and atmosphere. Hence, for a rigorous description of geochemical cycles and to understand the rules governing these exchanges, data on the distribution of elements and isotopes between coexisting minerals, fluids, and melts are a prerequisite. These physicochemical properties are determined in various projects in co-operation with other groups at the GFZ and (inter)national partners. Our approach is to integrate the experimental investigations with field-studies and numerical simulations.