Staurolite-rich metapelites near Rangeley, Maine, USA, have three basic types of crystal size distributions that provide insight into the mechanisms that control nucleation and growth during metamorphism.  An early Devonian period of regional heating (M2 metamorphism) produced more or less equant staurolite about ½ cm in diameter that are evenly distributed throughout individual compositional layers in a hand specimen. These M2 staurolites were later affected by hydrothermal systems and thermal gradients related to intrusion of late Devonian plutons (M3 metamorphism).  Rocks with M2 staurolite located far from the M3 intrusions were rehydrated at M3 garnet and biotite grade conditions; rocks with M2 staurolite at an intermediate distance from the M3 intrusions were unchanged because M3 Tmax  was at staurolite grade conditions; and rocks close to the M3 intrusions  experienced prograde metamorphism at sillimanite grade conditions[1].  Late M3 (M3+) staurolite growth in the early M3 garnet zone is produced by heating due to small local intrusions or advective flow.  Heating due to late M3 intrusions produce many small (~0.1 mm) staurolites concentrated in early M3 chlorite + muscovite pseudomorphs after M2 staurolites; heating due to advective fluid flow produces large (~1cm) staurolites distributed randomly throughout a hand specimen irrespective to the location of early M3 retrograde pseudomorphs after staurolite. These different patterns are produced by differences in the scale of local equilibrium, which influenced staurolite nucleation and growth as the late M3 staurolite isograd was overstepped in the M3 garnet zone.  Rocks near late M3 intrusions, where the heating rate was rapid, but with little advective flow, had small domains of equilibrium.  This produced clusters of small crystals where nucleation was strongly influenced by local compositional heterogeneity due to chlorite + muscovite pseudomorphs after M2 staurolite.   Conversely, rocks where heat was advectively transported along late M3 fluid transport paths have large domains of equilibrium due to the advective transport, so fewer staurolites nucleated before significant growth began and nucleation patterns were unaffected by the local compositional heterogeneity due to the early M3 chlorite + muscovite pseudomorphs after M2 staurolite.