A major episode of TTG magmatism took place in Bonai Gneissic Complex around 3368 Ma, followed by granitic magmatism around 3331 Ma. The emplacement and evolution of the BGC were coeval with granitoid magmatism from the central part of the Singhbhum Craton. Whole rock geochemical data identify both high- and low-HREE TTGs in both the BGC and OMTG to the west and east of the IOG basin, respectively. The trace element systematics of high-HREE Bonai TTG are similar to those of Icelandic dacites, suggestive of their derivation from a garnet free, plagioclase rich amphibolite. The low-HREE TTGs of the BGC and OMTG were derived from an amphibolite source with varying amounts of garnet. The potassic granites of the BGC were sourced from the older TTGs, which had undergone partial melting at a shallow depth. The evolution of the BGC and OMTG can be attributed to the partial melting under a thickened mafic crust and show dome and keel structures, which support the origin of these Paleoarchean granitoids in a stagnant lid regime. High geothermal gradients induced by heat supplied by mantle upwelling appear to have induced the melting of the thickened crust, to form the TTG. Delamination induced mafic–ultramafic underplating resulted in melting of early formed TTGs, to form the younger potassic granites of the BGC at ~ 3.33 Ga.
The distribution of Paleoarchean TTGs from the Pilbara, Kaapvaal, Western Dharwar and Singhbhum cratons
Ajay Dev Asokan, Satya Narayana Mahapatro, M Ram Mohan, Alexander Rocholl, Michael Wiedenbeck, Jayanta Kumar Nanda, Precambrian Research 366 (2021) 106429;