ABSTRACT
The Archaean, which spans the time from the formation of the Earth to c. 2600 Ma ago, was a time of crucial importance in the formation of the Earth’s crust and mantle. The most ancient dates on Archaean formations were obtained from detrital zircons from Archaean metasediments. The upper boundary of the transition from an Archaean type of geodynamics and magmatism to a Proterozoic type remains the subject of debate. Within the ancient shields two types of Archaean structural terrane have been distinguished: granite–greenstone and granulite–gneissic. They differ in their internal structure, their structural and metamorphic history, the ratio of exogenetic to endogenetic factors in the generation of crustal material and the type and form of the igneous activity and metallogeny. Archaean granite–gneiss areas are generally composed of 80–90% peculiar “grey gneisses”, which are actually plagiogneisses of tonalite–trondhjemite-granodiorite composition.
