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Holenarsipur Nucleus (HN) is one of the oldest part (3.5–3.1 Ga) of the continental crust of India. It is made up of mafic–ultramafic-komatitic (3.35 Ga) greenstone belts, migmatitic TTG (tonalite–trondhjemite–granodiorite 3.3 Ga) and diapiric trondhjemites (3.1 Ga). New major, trace and REE data on these rocks presented here provide constraints on adakite–TTG connection model and petrogenesis of these rocks of HN, in addition to recycling of the Early-Mesoarchaean basaltic crust and evolution of Mesoarchaean continental crust. Although of two different ages, the chemical characteristics of the migmatitic TTGs and diapiric trondhjemites of the HN resemble with the Archaean and Cenozoic high silica adakites (HSA), and the adakites from two Neoarchaean greenstone belts of Dharwar Craton, they also display similarities with the Early-Mesoarchaean TTGs from different cratons. Based on the compositional variations observed in TTG and diapiric trondhjemites of HN, we propose that plume fed, basaltic and/or basaltic komatiitic oceanic crust/slab flatly (shallow angle) subducted and melted under high Archaean geothermal regime to produce TTGs. Identification of HSA in 2.7 Ga old greenstone belt subduction complexes that are compositionally similar to TTG, suggests the possibility of continuation of this process into Neoarchaean and supports a genetic connection between TTG and adakites. |
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