Age-metallicity (top row) and age-[Mg/Fe] (bottom row) relations for in situ stars (grey shading) and the five most significant mergers (coloured areas). The total stellar mass of the merger debris at the time of the merger (log₁₀(M_*/M_⊙)) is mentioned in the legend in each top panel. Mean values are shown by the coloured solid curves (except for the black one, which corresponds to the in situ stars). The grey-scale for the in situ stars represents the mean galactocentric distance in the units of the disc scale lengths from Libeskind et al. (2020), as seen in the colour bars on the right, while the black dashed curves correspond to the 3σ around the mean. For the accreted populations, there is no shading and the boundaries correspond to 3σ around the mean.