ORIGIN OF ARCHAEAN POTASSIC GRANITE FROM BUNDELKHAND CRATON, CENTRAL INDIA: CONSTRAINTS FROM GEOCHEMICAL MODELLING USING MELTS FAMILY OF ALGORITHMS

Abstract

he Bundelkhand craton, at the North-Central part of India is a major crustal domains of Indian Peninsula. The craton mostly comprise of different types of granitoidsincluding tonalite-trondhjemite-granodiorite(TTG) gneisses and intrusive potassic granite, which are tectonically intercalated with suprarustal units. Supracrustal units mostly comprise mafic volcanics. TTG gneisses from the terrain show ages of crystallisation at -3.3, 3.2, 3.0 Ga while the potassic granite intruded at -2.5 Ga. Present study concentrates on the origin of the potassic granite, a rock type characteristically found from Neoarchaean onwards and hence holds probable testimony of the initiation of plate tectonice on Archaean Earth. The study of the geochemical signatures of the rocks of the Archaean-Proterozoic boundary is necessary to understand the early Earth's plate tectonics and its precise commencement episode. Initial field observation based structural studies and study of the deformational history of the outcrops concluded the change in rheology of the Archaean crust coeval with different generations of folding. Major and trace element modelling was conducted considering fractional crystallization as the igneous process for genesis of the potassic granites from trondhjemitic melt as its precursor. In the process MELTS Algorithims were used. Results from modelling affirm the generation of potassic granites from trondhjemitic magma through fractional crystallization at varying depths. Viscosity studies reveal the strengthening of the continental crust concurrent with formation of the potassic granites and development of shear bands. Shear bands probably acted as the weak zones where movements of crust were initiated. Such domains of strain concentration probably led to initiation of plate tectonics in Neoarchaean,