  We derived stellar ages and metallicities [Z/H] for $\sim$70 passive early
type galaxies (ETGs) selected from VANDELS survey over the redshift range
1.0$<$$z$$<$1.4 and stellar mass range 10$<$log(M$_*$/M$_\odot$)$<$11.6. We
find significant systematics in their estimates depending on models and
wavelength ranges considered. Using the full-spectrum fitting technique, we
find that both [Z/H] and age increase with mass as for local ETGs. Age and
metallicity sensitive spectral indices independently confirm these trends.
According to EMILES models, for 67 per cent of the galaxies we find
[Z/H]$>$0.0, a percentage which rises to $\sim$90 per cent for
log(M$_*$/M$_\odot$)$>$11 where the mean metallicity is [Z/H]=0.17$\pm$0.1. A
comparison with homogeneous measurements at similar and lower redshift does not
show any metallicity evolution over the redshift range 0.0<z<1.4. The derived
star formation (SF) histories show that the stellar mass fraction formed at
early epoch increases with the mass of the galaxy. Galaxies with
log(M$_*$/M$_\odot$)$>$11.0 host stellar populations with [Z/H]>0.05, formed
over short timescales ($\Delta{t50}$$<$1 Gyr) at early epochs (t$_{form}$$<$2
Gyr), implying high star formation rates (SFR$>$100 M$_\odot$/yr) in high mass
density regions (log($\Sigma_{1kpc}$)$>$10 M$_\odot$/kpc$^2$). This sharp
picture tends to blur at lower masses: log(M$_*$/M$_\odot$)$\sim$10.6 galaxies
can host either old stars with [Z/H]$<$0.0 or younger stars with [Z/H]$>$0.0,
depending on the duration ($\Delta{t50}$) of the SF. The relations between
galaxy mass, age and metallicities are therefore largely set up ab initio as
part of the galaxy formation process. Mass, SFR and SF time-scale all
contribute to shape up the stellar mass-metallicity relation with the mass that
modulates metals retention.
