The paper is devoted to modelling of growth zoning in garnet from medium-grade metapelites from Northern Ladoga area. As a part of modelling, Mn concentration profiles in garnet porphyroblasts of various sizes were calculated with THERMOCALC. Furthermore, kinetics of porphyroblast growth were analyzed and the effect of phase transitions involved on zoning patterns was studied. On this basis, the clockwise P-T-t trajectory was revealed. The paper discusses the estimation of metamorphic crystallization timing and the significance of cooling history as a factor of modification of garnet zoning as well as the tectonic implications of the model path.