  CFHT Megacam data in (g',r',i') are used to obtain deep, wide-field
photometry of the globular cluster system (GCS) around M87. A total of 6200 GCs
brighter than M_I = -8.5 are included in the study, essentially containing
almost the entire bright half of the total GC population in the galaxy. The
classic bimodal metal-poor and metal-rich sequences of GCs show up clearly;
while the spatial distribution of the GCs can be traced detectably outward to
more than 100 kpc, the blue, metal-poor subpopulation is very much more
spatially extended than the red subpopulation. Both the red and blue GC
subsystems have radial metallicity gradients, where mean heavy-element
abundance scales with projected galactocentric distance as Z ~ R^{-0.12} (blue)
and R^{-0.17} (red). The blue sequence exhibits a strongly significant
mass/metallicity relation (MMR) in which the mean metallicity gradually
increases with cluster luminosity as Z ~ L^{0.25 \pm 0.05} for the luminosity
range M_I < -10. However, this relation is also clearly nonlinear, becoming
vertical at fainter levels. The MMR can be understood as the result of
self-enrichment within the most massive metal-poor GCs during their formation.
In giant elliptical galaxies, the red GCs are likely to represent a broad
composite population formed during several major starbursts. If so, the red
sequence might display a population-based MMR that could in principle be either
positive or negative.
