Abstract In the last decade, the considerable amount of ultrahigh pressure terrains found around the world (Liou et al., 1998) and recent findings of mineral inclusions suggesting equilibration pressures up to more than 20 GPa (e.g. Stachel et al., 2000) have led to an increasing interest in petrological tools to be used to unravel the P-T evolution at extreme conditions. The expected resolution of such tools should provide a key for understanding tectonic processes responsible for the dynamics of UHP terrains.