Palaeoproterozoic rift-related alkaline magmatism in Bari area, Son valley, Central India

Abstract

Earlier studies on Palaeoproterozoic (∼1800 Ma) alkaline (shoshonitic) rocks comprised of limited petrochemical data on the Bari syenite and other contiguous felsic rocks emplaced in anorogenic rift setting along the Son-Narmada North Fault (SNNF). Using new major and trace element data-sets, this study offers means of study of origin, source of magma, tectonic settings and geodynamic implications. The major oxide chemistry grouped Bari rocks into high alkali, but low CaO bearing peraluminous alkaline rocks. These rocks represent high abundance of HREE, Zr, Nb, Ga, Y, Eu, Ba and Sr. Primitive mantle normalized REE and trace elemental patterns correspond to A-type suite, suggesting origin of the magma mainly from the mantle. Significantly, anomalous Th/U and Rb/Cs values revealed crustal contamination of the melt, derived from partial melting of the mantle. Moreover, binary data plots between La vs. La/Sm and La vs. La/Yb are pointing towards crustal assimilation which was concomitant with the fractional crystallization of the mantle derived melt. Thus, crustal contamination coupled with the fractional crystallization of the melt mainly contributed to the formation of syenite melt. But, a high degree of partial melting of the lower crust was primarily responsible for the formation of Bari granite. The enrichment of incompatible elements in the syenite rocks suggests involvement of mantle metasomatism in their genesis. The magmatic processes related to the formation of syenite, lamprophyre, ultramafics, mafic and granite bodies were operative in the diverse magmatic realm and initiated earlier at the waning stage of the Mahakoshal orogeny and continental rifting, but magma emplaced later during Post-Mahakoshal orogeny and Pre-Vindhyan sedimentation that also in a rifted basement of the Bundelkhand craton at ∼1800 Ma during the amalgamation of the Columbian Supercontinent.