The Tonalite-Trondhjemite-Granodiorite (TTG) Suite and Archaean Island Continents

Abstract

Since the 1970s it was realized the bulk of Archaean granitoids intruded into Archaean supracrustal sequences have typically Na-rich composition, comprising tonalite, trondhjemite and granodiorite, the so-called TTG suite (Glikson and Shertaon, Earth Planet Sci Lett 17:227–242, 1972; Hanson, Geochim Cosmochim Acta 39:325–362, 1975; Arth and Hanson, Geochim Cosmochim Acta 39:325–362, 1975; Barker, Trondhjemite: a definition, environment and hypotheses of origin. In: Barker F (ed) Trondhjemites, dacites and related rocks. Elsevier, Amsterdam, pp l–12, 1979; Glikson, Earth Sci Rev 15:1–73, 1979a; Glikson, J Geol Soc India 20:248–255, 1979b; Moyen et al, TTG plutons of the Barberton granitoid-greenstone terrain, South Africa. In: Van Kranendonk MJ, Smithies RH, Bennett VC (eds) Earth’s Oldest Rocks. Developments in Precambrian geology 15. Elsevier, Amsterdam, pp 607–667, 2007). Petrological studies (Green and Ringwood, Contrib Mineral Petrol 18:105–162, 1977), coupled with geochemical and isotopic evidence, demonstrate a derivation of TTG from mafic crustal materials containing isotopic mantle signatures. The evolution of TTG igneous activity is closely correlated with volcanic events within associated greenstone belts. By contrast post-kinematic Archaean granitoids typically comprise quartz monzonites and granites enriched in the large ion lithophile elements (LIL) and display field and petrological evidence for derivation by partial melting of older TTG batholiths. Pre-3.2 Ga TTG tend to occur as oval plutons containing abundant mafic enclaves, with best examples in the Zimbabwe Craton and around the Barberton Greenstone Belt, Kaapvaal Craton, South Africa. By contrast late Archaean granitoids Post-kinematic granitoids are commonly emplaced along boundaries between TTG and supracrustal enclaves, or at high structural levels of batholiths, as is the case with the Lochiel Granite in Swaziland.