Topological analysis of the iron phase diagram in the subsolidus region shows that the slopes of stable univariant equilibria impose constraints for the metastable growth of other phases upon quenching. If the relative slopes of equilibrium univariant curves and the relative positions of invariant points are known or can be estimated, pressure-temperature regions for the potential growth of metastable phases may be delimited. The results are applied to the proposed stability field of &bgr;-iron.¿ 1997 American Geophysical Union