M. Raith

Crustal architecture and evolution of the Eastern Ghats Belt and adjacent regions of India

Abstract Extending along the east coast of peninsular India, the Eastern Ghats expose a deep section through a composite orogenic belt that once formed part of the Proterozoic mobile belt system within East Antarctica and East India. The critical evaluation of the existing geological and isotopic data strongly suggests that this orogenic belt includes not only the granulite facies Eastern Ghats Belt but also the Nellore-Khammam Schist Belt and lower grade units at the southern margin of the Singhbhum Craton. The present authors propose its subdivision into four crustal provinces with widely different geological evolutions. The Rengali and Jeypore Provinces formed at the margin of the Bhandara Craton in the Late-Archaean. In the Krishna Province, volcanosedimentary rocks equivalent to the Cuddapah Supergroup accumulated, probably on the Dharwar Craton in the Palaeoproterozoic, and the major tectonometamorphic event took place between 1.67 and 1.55 Ga, subsequent to a short-lived igneous activity. The Eastern Ghats Province, which shows considerable similarities with the Rayner Province of East Antarctica, was strongly affected by pervasive deformation, high-grade metamorphism and crustal-derived magmatism between 1.1 and 0.9 Ga, which extensively modified the crustal structure of present eastern peninsular India. Neoproterozoic and Early Phanerozoic tectonothermal activities were largely restricted to pre-existing shear zones, but the present configuration of the composite orogenic belt may have been achieved only during the Pan-African Orogeny.

Evolution of the Continental Crust in the Proterozoic Eastern Ghats Belt, India and new constraints for Rodinia reconstruction: implications from Sm–Nd, Rb–Sr and Pb–Pb isotopes ☆

Abstract For this study Nd, Sr and Pb isotope compositions were analyzed for ortho- and paragneisses from the Eastern Ghats Belt of India in order to determine its crust formation and crustal evolution. This belt represents a Proterozoic orogen that extends along the east coast of Peninsular India and forms part of the mobile belts in East Gondwana and Rodinia. The Eastern Ghats Belt was affected by Mesoproterozoic granulite facies metamorphism in the western segment (Western Charnockite Zone) and a Grenvillian regional-scale high-grade event in the central and eastern segments (Western Khondalite Zone, Charnockite Migmatite Zone and Eastern Khondalite Zone) as well as a local Pan-African overprint. The results of the isotope studies are used for the large-scale reconstruction of the indo-antarctic part of the Rodinia supercontinent. Based on Nd model ages and Pb isotope ratios from leached feldspars four crustal domains can be distinguished in the Eastern Ghats Belt. These domains can in part be correlated with the lithological division of the belt: (1) The Western Charnockite Zone south of the Godavari Graben is characterized by Nd model ages between 2.3 and 2.5 Ga for orthogneisses and 2.6 and 2.8 Ga for metasediments (Domain 1). The Pb isotopes are primitive indicating reworking of dominantly Archean and mixing with minor Proterozoic material; (2) North of Godavari Graben Nd model ages for orthogneisses are significantly higher with values ranging from 3.2 to 3.9 Ga. The Pb isotopes are strongly retarded; (3) The north-eastern parts of the Charnockite Migmatite Zone and Western Khondalite Zone form a distinct and almost homogeneous crustal domain (Domain 3) with Nd model ages between 1.8 and 2.2 Ga; (4) Between the isotopically homogeneous terranes stretches a broad transition zone (Domain 2) enclosing parts of the Western Khondalite Zone, Charnockite Migmatite Zone and Eastern Khondalite Zone. The Nd model ages for metasediments (2.1–2.5 Ga) are younger than paragneiss ages of the adjoining Western Charnockite Zone. The Nd model ages for orthogneisses (1.8–3.2 Ga) display a large spread, which is consistent with the Pb isotope signatures that indicate mixing of Archean with Proterozoic material. The border zone between Domain 3 and the Archean Eastern Indian Craton forms a second transition zone (Domain 4) characterized by metasediments with Nd model ages between 2.2 and 2.8 Ga and orthogneisses with model ages around 3.2 Ga. Reworking of Archean crustal material is most intense along the border zones of the belt and ‘juvenile’ material is more dominant away from the orogenic front. This scenario is indicative of an active continental margin setting for the two Proterozoic episodes of orogenesis in the Eastern Ghats Belt. A correlation of Domain 3 with the Rayner Complex and the Prydz Bay region, Antarctica, for the early crustal evolution is supported by the similarity of the isotope signatures. The Napier Complex is very different to the Eastern Ghats Belt and an early joint evolution of these terranes is ruled out on the basis of the Pb–Pb and Sm–Nd systematics.

Progressive Metamorphism of Mafic Rocks from Greenschist to Granulite Facies in the Dharwar Craton of South India

In the Archean Dharwar craton of southern India N-S trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2.5 Ga ago. The progressive changes in the assemblages and mineral chemistry of metabasites was studied in a N-S traverse covering the Chitradurga and Nagaman-gala belts, the Sargur area, and the Nilgiri Hills. Towards the south with increasing metamorphic grade greenschists (

Age of emplacement of massif-type anorthosites in the Eastern Ghats Belt, India: constraints from U–Pb zircon dating and structural studies

chl + act + ab + ep \pm carb

The Granulite Terrane of the Nilgiri Hills (Southern India): Characterization of High-Grade Metamorphism

, qtz) give way to amphibolites (

On the origin of ‘arrested’ charnockitization in the Chilka Lake area, Eastern Ghats Belt, India: a reappraisal

hbl + plag \pm qtz