  We present a cosmologically motivated model for the hierachical formation of
the stellar halo which includes a semi-analytic treatment of galactic chemical
enrichment coupled to numerical simulations that track the orbital evolution
and tidal disruption of satellites. A major motivating factor in this
investigation is the observed systematic difference between the chemical
abundances of stars in satellite galaxies and those in the Milky Way halo.
Specifically, for the same [Fe/H] values, stars in neighboring satellite
galaxies display significantly lower [alpha/Fe] ratios than stars in the halo.
  We find that the observed chemical abundance patterns are a natural outcome
of the process of hierarchical assembly of the Galaxy. This result follows
because the stellar halo in this context is built up from satellite galaxies
accreted early on (more than 8-9 Gyr ago) and enriched in alpha-elements
produced in Type II supernovae. In contrast, satellites which survive today are
typically accreted late (within the last 4-5 Gyr) with nearly solar [alpha/Fe]
values as a result of contributions from both Type II and Type Ia supernovae.
We use our model to investigate the abundance distribution functions (using
both [Fe/H] and [alpha/Fe] ratios) for stars in the halo and in surviving
satellites. Our results suggest that the shapes and peaks in the abundance
distribution functions provide a direct probe of the accretion histories of
galaxies.
