Petrogenesis of ultramafic-mafic to felsic plutonic rock associations from southern portion of Chhotanagpur Gneissic Complex in Central India: A multi-stage crust-mantle interaction process

Abstract

A granite-granodiorite-gabbro-ultramafic rock association occurs in the southern sector of Chhotanagpur Gneissic Complex in Central India. Field relations show mingling and mixing of mafic and granodioritic magmas along the contacts of the intrusives. Petrographic studies, coupled with analyses of phase compositions and bulk rock major and trace element compositions favor origin of mafic magma from partial melting of sub-continental hybridized lithospheric mantle and subsequent two stage emplacement. Initial ponding of mafic magma at basal crust elevated the geothermal gradient so as to cause partial melting of lower crustal materials and generation of granodioritic melt. Simultaneous emplacement of granodioritic and mafic magmas tapped from basal crustal reservoir at mid-crustal depth resulted in restricted mingling-mixing along the contacts of the contrasting magma types locally producing rocks of dioritic composition. The mode of evolution of this cogenetic mafic-felsic association, when combined with available geochronological data, has important implications in demarcation of the extent of Grenvellian orogen that resulted in amalgamation of the Southern Crustal Province of India (SCP) with the Bundelkhand Craton or Northern Crustal Province (NCP).