Comparison of the distribution of stars in CaMD for cluster #12 (blue) and substructure A (red). The black line represent the isochrone that best reproduces the distribution of stars in the CaMD for substructure A (see Sect. 3.1). The inset panel shows the distributions of colours with respect to the best fit isochrone for both structures. We mark low-metallicity stars ([Fe/H] < −1.4) with blue crosses.