Structural insights into sodium rich silicate carbonate glasses and melts : a combined study of trace element in situ XAFS and molecular dynamics Carbonate rich silicate and carbonate melts play a crucial role in deep Earth magmatic processes and their melt structure is a key parameter as it controls physical and chemical properties. Carbonate rich melts can be strongly enriched in geochemically important trace elements. The structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses which are usually employed for structural investigations. This thesis investigates the influence of CO2 on the local environments of trace elements contained in silicate glasses with variable CO2 concentrations as well as in silicate and carbonate melts. The compositions studied include sodium rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at Oldoinyo Lengai volcano Tanzania. The local environments of the three elements yttrium (Y) lanthanum (La) and strontium (Sr) were investigated in synthesized glasses and melts using X ray absorption fine structure (XAFS) spectroscopy. Especially extended X ray absorption fine structure spectroscopy (EXAFS) provides element specific information on local structure such as bond lengths coordination numbers and the degree of disorder. To cope with the enhanced structural disorder present in glasses and melts EXAFS analysis was based on fitting approaches using an asymmetric distribution function as well as a correlation model according to bond valence theory. Firstly silicate glasses quenched from high pressure temperature melts with up to 7.6 wt % CO2 were investigated. In strongly and extremely peralkaline glasses the local structure of Y is unaffected by the CO2 content (with oxygen bond lengths of ~ 2.29 Å). ...