Evolution of the particles touched by the supernova feedback is shown for different element ejection schemes (see text). The upper parts of the plots show the radius as a function of the metallicity. The lower parts indicate the [Mg/Fe] ratio as a function of [Fe/H]. The black dots show particles at t₁, just after the first explosion; the blue dots at t₂, just before the second explosion; the green dots at t₃, just after the second explosion; and the red dots at t₄, at the end of the run. The histograms on the upper right indicate the metallicity distribution function at t₄.