The temporal and spatial evolution of sequentially and single ion implanted Cd and Se concentration distributions into thermally grown SiO2 on (001)-Si were investigated. Ex-situ rapid thermal annealing was performed to initiate the reaction-diffusion driven material transport, nanocrystal nucleation and growth. Finally this leads to the formation of buried distinct layers of CdSe nanocrystals. The spatiotemporal evolution of the concentration distributions were quantitatively analyzed by dynamic Secondary Ion Mass Spectrometry (SIMS). It will be shown, that there is a correlated diffusion of Cd and Se when both elements were implanted in overlapping concentration profiles, whereas the single implanted Cd and Se exhibit a completely different diffusion behaviour. In the region of the supersaturated solid solution reaction to thermodynamically stable CdSe clusters takes place. The steep concentration gradient provokes indiffusion of the stoichiometric compound. In the case of a surplus of Cd over Se and long annealing times self-organized, nearly periodic and correlated concentration variations of Cd and Se can be observed. Comparison of the profiles indicate that this pattern formation is controlled by the diffusion and precipitation of the over stoichiometric Cd.