Diffusion velocities (in cgs units) below the surface convective zone in the Montreal (dashed curves) and TGEC (solid curves) 30 Myr-models represented in Fig. 4. The vertical lines locate the bottom of the completely mixed region. The peaks observed for Ca and Fe correspond to sign changes in the diffusion velocities: the Ca diffusion velocity is positive for log (ΔM/M) ≲ −6 and −3.5 ≲ log (ΔM/M) ≲ −2.5. The Fe diffusion velocity is positive for −7 ≲ log (ΔM/M) ≲ −4.5.