Archean Granite Plutons

Potassium-rich granite, contrary to some opinions expressed in the past is a widespread and voluminous constituent of Archean cratons. Some of the granite occurs as highly metamorphosed banded gneiss but the majority forms massive to moderately foliated, medium- to coarse-grained plutons that largely retain an igneous mineralogy. Most of the plutons have areal exposures of 5-500 km² but a few exceed 1000 km². Condie (1993) estimated that granite plutons make up ∼20% of the rock exposed in Archean shields, placing them far ahead of tholeiite (∼10%) and second only to the tonalite-trondhjemite-granodiorite (TTG) suite (∼50%) in abundance. Until recently, there have been only a handful of detailed studies of Archean granite plutons and, with few exceptions, almost no attempt to place what is known about these rocks in a general context.