We analyze age and metallicity estimates for an unprecedented database of some 5.5 million stars distributed throughout the Large Magellanic Cloud ( LMC ) main body , obtained from CCD Washington CT _ { 1 } photometry , reported on in Piatti et al .
2012 .
We produce a comprehensive field star Age-Metallicity Relationship ( AMR ) from the earliest epoch until \sim 1 Gyr ago .
This AMR reveals that the LMC has not evolved chemically as either a closed-box or bursting system , exclusively , but as a combination of both scenarios that have varied in relative strength over the lifetime of the galaxy , although the bursting model falls closer to the data in general .
Furthermore , while old and metal-poor field stars have been preferentially formed in the outer disk , younger and more metal-rich stars have mostly been formed in the inner disk , confirming an outside-in formation .
We provide evidence for the formation of stars between 5 and 12 Gyr , during the cluster age gap , although chemical enrichment during this period was minimal .
We find no significant metallicity gradient in the LMC .
We also find that the range in the metallicity of an LMC field has varied during the lifetime of the LMC .
In particular , we find only a small range of the metal abundance in the outer disk fields , whereas an average range of \Delta [ Fe/H ] = +0.3 \pm 0.1 dex appears in the inner disk fields .
Finally , the cluster and field AMRs show a satisfactory match only for the last 3 Gyr , while for the oldest ages ( > 11 Gyr ) the cluster AMR is a remarkable lower envelope to the field AMR .
Such a difference may be due to the very rapid early chemical evolution and lack of observed field stars in this regime , whereas the globular clusters are easily studied .
This large difference is not easy to explain as coming from stripped ancient Small Magellanic Cloud ( SMC ) clusters , although the field SMC AMR is on average \sim 0.4 dex more metal-poor at all ages than that of the LMC but otherwise very similar .