  Abundances for alpha-elements and Fe in about 150 field subdwarfs and early
subgiants with accurate parallaxes and kinematic data are used to discuss the
run of abundance ratios in metal-poor stars in the solar neighborhood. Based on
kinematics, we separated stars into two populations: the first one has a
positive velocity of rotation around the galactic center, and it is likely to
be related to the dissipational collapse of the galaxy; the second one has
either negligible or negative rotational velocity, and it is likely related to
an accretion component. The two populations show a large overlap in
metallicity. However, they show distinct chemical properties. For the first
population we found that there are close correlations (with small scatters
around) of the rotational velocity with metallicity and with the Fe/alpha
abundance ratio: this might be a signature of a not very fast collapse of the
progenitor clouds, with enough time for a significant contribution by SNe Ia,
although this result needs to be confirmed by a 3-D/non-LTE study. On the other
side, the second population exhibits a larger scatter in both the above
mentioned relations, and on average, a larger Fe/alpha ratio at a given
metallicity, suggesting a larger scatter in ages. We argue that the lack of
stars with moderate rotational velocities and high Fe/alpha abundance ratios is
due to the short merging time for protogalactic clouds with prograde motion,
while the presence of a group of counter-rotating stars with this
characteristics indicates a much longer typical lifetimes for protogalactic
fragments having such a motion. Finally, we found that perigalactic distances
correlate with the Fe/alpha abundance ratios better than the apogalactic
distances.
