Petrogenesis of mafic magmatic enclaves of the Bundelkhand granitoids near Orchha, Central Indian shield: evidence for rapid crystallization

Abstract

AbstractAn attempt has been made to understand the origin and emplacement of the widespread mafic magmatic enclaves (MMEs) in the Neoarchean–Palaeoproterozoic Bundelkhand granitoids in the central Indian shield. These MMEs are very fine grained in texture, elliptical and ovoidal in shape and have a very sharp contact with the host granitoids. The MMEs exhibit sub-ophitic texture, acicular apatite and overgrowth of orthopyroxene over olivine crystals pointing towards a rapid crystallization of the MMEs magma in the granitoid magma. The host granitoids are calc-alkaline while the MMEs are tholeiitic, indicating contrasting geochemical composition. Low concentration of Rb, Sr, Ba and K in MMEs points away from the magma mixing with the granitoid magma. Both MMEs and host granitoids are metaluminous and are formed in a subduction zone environment. Although both MMEs and the granitoids were formed at the same time as the mafic magma was injected into the granitoid magma which was still crystallizing (semimolten stage), negligible to no mixing took place between the two contrasting magmas. We propose that the MMEs in the Bundelkhand granitoids are the result of rapid crystallization of the mafic magma in the cooler felsic one.