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[Abridged] In this first paper of this series, we present a new approach forstudying the chemo-dynamical evolution in disk galaxies, which consists offusing disk chemical evolution models with compatible numerical simulations ofgalactic disks. This method avoids known star formation and chemical enrichmentproblems encountered in simulations. Here we focus on the Milky Way, by using adetailed thin-disk chemical evolution model and a simulation in thecosmological context, with dynamical properties close to those of our Galaxy.We show that, due to radial migration from mergers at high redshift and thecentral bar at later times, a sizable fraction of old metal-poorhigh-[alpha/Fe] stars reaches the solar vicinity. This naturally accounts for anumber of recent observations related to both the thin and thick disks, despitethe fact that we use thin-disk chemistry only. Although significant radialmixing is present, the slope in the age-metallicity relation is only weaklyaffected, with a scatter compatible with recent observational work. While wefind a smooth density distribution in the [O/Fe]-[Fe/H] plane, we can recoverthe observed discontinuity by selecting particles according to kinematiccriteria used in high-resolution samples to define the thin and thick disks. Weoutline a new method for estimating the birth place of the Sun and predict thatthe most likely radius lies in the range 4.4 < r < 7.7 kpc (for a location at r= 8 kpc). A new, unifying model for the Milky Way thick disk is offered, whereboth mergers and radial migration play a role at different stages of the diskevolution. We show that in the absence of early-on massive mergers the verticalvelocity dispersion of the oldest stars is underestimated by a factor of ~2compared with observations. We can, therefore, argue that the Milky Way thickdisk is unlikely to have been formed through a quiescent disk evolution.

Chemodynamical evolution of the Milky Way disk I: The solar vicinity