The Mayurbhanj Granite - A Precambrian Batholith in Eastern Inola

The term 'Mayurbhanj Granite' is proposed here for a batholithic body of biotite-amphibole-(stilpnomelane) granite grading to alkali-feldspar granite which covers nearly 1000 sq. km area in the northern part of Mayurbhanj district, Orissa. The batholith shows intrusive relationship with the adjoining Singhbhum Granite, Dhanjori Group gabbro-anorthosite and the Singhbhum Group metamorphites, and is made up of three units which were successively emplaced within the same magmatic cycle: (a) fine-grained, homophanous biotite-ferrohastingsite (-stilpnomelane) microgranite, in part granophyric, (b) coarse-grained, homophanous to well-foliated ferrohastingsite-biotite granite, which is porphyroblastic and gneissos in the east, and (c) 'biotite aprogranite injections within the porphyroblastic gneisses in the east. The second unit is by far the largest and was intruded synkinematically with respect to the second-generation folding in the Singhbhum Group metamorphites, probably about 1.1 × 10⁹ years ago.