Same as in Fig. 3 but considering a smaller gas infall mass for the third infall – it accounts for 15% of the total low-α sequence barionic mass – and a larger SFE (ν₃ = 0.8 Gyr⁻¹). The inset also reports the normalised star formation history with the different evolutionary phases coloured as in the main plot [Si/Fe] versus [M/H]. The value of the SFE associated to the low-α phase I (indicated with the blue dashed line) is ν₂ = 1 Gyr⁻¹. Vertical dashed lines indicate the ages corresponding to yellow points.