Geology of the Contact between the Eastern Ghats Belt and North Orissa Craton, India

The contact region of tile Eastern Ghats Belt (EGB) with the North Orissa Craton (NOC) in Orissa State was studied and certain new observations have been made. The contact is represented by a wide zone affected by several east-west running faults with fault fragments of both blocks interfingcred with each other. Portions of the fault zone have later given rise to Gondwana graben in which coal-bearing sediments were deposited covering the contacts. The stratigraphic relation between the two crustal blocks was difficult of interpretation because of intermingling of the fault slices and concealment of the contacts by granitic intrusion, Gondwana sedimentation and lateritic cover.

The Eastern Ghats Belt (EGB) is made up of granulite facies rocks consisting principally of khondalites, leptynites, quartzites, gamet-biotite schists, basic granulites, charnockites and gneisses, all migmatized to different degrees. They could be distinguished into two different assemblages: the Rengali assemblage, forming the northernmost fringe of the EGB and the Angul assemblage lying to the south of the Gondwana graben. Both differ in their lithologic characteristics. The North Orissa craton, on the other hand, consists of several sequences of low-grade supracrustals with or without Banded Iron Formation (BIF) associated with granitic intrusion of more than one generation. At places within the fault zone between the two blocks there are typical intrusions of nepheline syenite and chromite-bearing ultrabasics.

A tentative geological account around the contact of the two major crustal blocks has been presented. It is believed that the Eastern Ghats granulite rocks formed earlier to the BIF-bearing supracrustals and associated granite intrusives. Migmatization, charnockitization and alkali plutonism etc. were late Proterozoic events in the EGB (1.0 Ga-0.8 Ga) related to deep seated fault tectonics along the contact.