  The most massive elliptical galaxies show a prominent multi-modality in their
globular cluster system color distributions. Understanding the mechanisms which
lead to multiple globular cluster sub-populations is essential for a complete
picture of massive galaxy formation. By assuming that globular cluster
formation traces the total star formation and taking into account the radial
variations in the composite stellar populations predicted by the Pipino &
Matteucci (2004) multi-zone photo-chemical evolution code, we compute the
distribution of globular cluster properties as a function of galactocentric
radius. We compare our results to the spectroscopic measurements of globular
clusters in nearby early-type galaxies by Puzia et al. (2006) and show that the
observed multi-modality in globular cluster systems of massive ellipticals can
be, at least partly, ascribed to the radial variation in the mix of stellar
populations. Our model predicts the presence of a super-metal-rich population
of globular clusters in the most massive elliptical galaxies, which is in very
good agreement with the spectroscopic observations. Furthermore, we investigate
the impact of other non-linear mechanisms that shape the metallicity
distribution of globular cluster systems, in particular the role of
merger-induced globular cluster formation and a non-linear color-metallicity
transformation, and discuss their influence in the context of our model
(abridged)
