Evidence for an early Archaean granite from Bastar craton, India

Granitoids in the early Archaean are believed to be potassium-poor tonalite-trondhjemite-granodiorite rocks. Only after continental crust attained sufficient thickness did true (relatively potassium-rich) granites form. No record of true granite prior to 3.4 Ga is available. We report a 3.6 Ga true granite from the Archaean Bastar craton in India. In contrast to the typical early Archaean granitoids, which are commonly deformed into gneisses, this granite is relatively undeformed. The age and composition of the granite implies that continental crust of the Bastar craton attained sufficient thickness to permit intracrustal melting at 3.6 Ga.