  We present spectroscopic ages, metallicities, and [alpha/Fe] ratios for 70
globular clusters in M31 that were derived from Lick line-index measurements.
In addition to a population of old (>10 Gyr) globular clusters with a wide
range of metallicities, from about -2.0 dex to solar values, we find evidence
for a population of intermediate-age globular clusters with ages between ~5 and
8 Gyr and a mean metallicity around [Z/H]=-0.6. We also confirm the presence of
young M31 globular clusters that were recently identified by Beasley et al.
(2004), which have ages <1 Gyr and relatively high metallicities around -0.4
dex. The M31 globular cluster system has a clearly super-solar mean
[alpha/Fe]=0.14\pm0.04 dex. Intermediate-age and young objects show roughly
solar abundance ratios. We find evidence for an age-[alpha/Fe] relation in the
sense that younger clusters have smaller mean [alpha/Fe] ratios. From a
comparison of indices, mostly sensitive to carbon and/or nitrogen abundance,
with SSP model predictions for nitrogen-enhanced stellar populations, we find a
dichotomy in nitrogen enhancement between young and old M31 globular clusters.
The indices of objects older than 5 Gyr are consistent with a factor of three
or higher in nitrogen enhancement compared to their younger counterparts. Using
kinematical data from Morrison et al. (2004) we find that the globular cluster
sub-population with halo kinematics is old (>9 Gyr), has a bimodal metallicity
distribution, and super-solar [alpha/Fe]. Disk globular clusters have a wider
range of ages, are on average more metal-rich, and have a slightly smaller mean
[alpha/Fe] ratio. (abridged)
