Numerische Untersuchung zur thermochemischen Konvektion in Mehrkomponenten-und Mehrphasensystemen am Beispiel erstarrender magmatischer Schmelzen

Dynamical differentiation processes are undoubtedly of key-importance with regard to the evolution of magmatic systems on all scales, ranging from small intrusional complexes to the global scale of the Earth's mantle. The origin of compositional zonation in silicic to intermediate-composition magma bodies is assumed to be related to the coupling between phase change and convection. Each kind and form of compositional zonation should be explainable with this coupling. The influence of the interaction between the chemically and thermally driven convection as well as between thermochemical convection and crystal fractionation on the evolution of a solidifying magma chamber and the final macrosegregation is the object of investigation in this thesis. A continuum model of convection with phase change has been developed and used to investigate the origin of compositional zonation. In this model a single set of conservation equations for mass, momentum, energy and species is solved by a finite element method in a simplified rectangular model domain in which cooling occurs through the sidewalls and the top and which is thermally and chemically disconnected from sources below. The equations are applicable to all regions simultaneously (solid, liquid, mixture). The chemical composition of the system is prescribed by the pure binary eutectic system diopside-leucite, which can frequently be found in the vicinity of subduction zones. The thermodynamic and transport properties of melts and mixtures in this two-component system have been incorporated explicitly into the dynamic model as far as advectional, diffusional and inter-phase transport are concerned. During environmental cooling different kinds of regions occur - pure solid, pure liquid and a mixture of both (mush) - characterized by a microstructure that depends on the conditions of solidification. (orig.)SIGLEAvailable from TIB Hannover: RA 1818(112) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman