  By means of N-body simulations, we show that radial migration in galaxy
disks, induced by bar and spiral arms, leads to significant azimuthal
variations in the metallicity distribution of old stars at a given distance
from the galaxy center. Metals do not show an axisymmetric distribution during
phases of strong migration. Azimuthal variations are visible during the whole
phase of strong bar phase, and tend to disappear as the effect of radial
migration diminishes, together with a reduction in the bar strength. These
results suggest that the presence of inhomogeneities in the metallicity
distribution of old stars in a galaxy disk can be a probe of ongoing strong
migration. Such signatures may be detected in the Milky Way by Gaia (and
complementary spectroscopic data), as well as in external galaxies, by IFU
surveys like CALIFA and ATLAS3D. Mixing - defined as the tendency toward a
homogeneous, azimuthally symmetric, stellar distribution in the disk - and
migration turns out to be two distinct processes, the effects of mixing
starting to be visible when strong migration is over.
