  We present an analytical and phenomenological model for metal enrichment in
halos based on hierarchical structure formation. This model assumes that
astration of normal stellar populations along with SNe II already occurs at
very high redshift. For halos that are not disrupted by SN II explosions, the
chemical evolution of the gas and stars is explicitly determined by the rate of
gas infall as compared with the astration rate and the corresponding rate of
metal production by SNe II per H atom in the gas. This model provides a good
description of the data on [Fe/H] for damped Ly alpha systems over a wide range
of redshift 0.5 < z < 5. For all halos not disrupted by SN II explosions, if
there is a cessation of gas infall, the metallicities of stars follow a bimodal
distribution. This distribution is characterized by a sharp peak at the value
of [Fe/H] corresponding to the time of infall cessation and by a broad peak at
a higher value of [Fe/H] corresponding to the subsequent period of astration
during which the bulk of the remaining gas forms stars. Such a distribution may
be compared to that observed for the Galactic halo stars. If the gas in a halo
is rapidly lost upon cessation of infall, then an assemblage of stars with a
very sharply-defined [Fe/H] value will be left behind. This assemblage of stars
may be accreted by a larger system and become a globular cluster of the larger
system. We also discuss the masses and metallicities of the globular clusters
in this model. (Abridged)
