Post-Grenvillean transpression in the Chilka Lake area, Eastern Ghats Belt—implications for the geological evolution of peninsular India

Abstract

Results of a combined structural and geochronological study of the area around the 0.79 Ga Chilka Lake anorthosite complex in the Eastern Ghats Belt of India place important constraints on the geological history of peninsular India. Th–U–Pb EPMA dating of monazites from the outer margin of the anorthosite complex and from country rocks reveals that the emplacement of the anorthosite occurred at the beginning of a protracted Middle Neoproterozoic tectono-magmatic event, encompassing leucogranite emplacement and/or cooling in the aureole of the anorthosite between 762 and 743 Ma and a fabric-defining transpressional deformation at 690–662 Ma. The progressive deformation was accompanied by granulite facies metamorphism. A thermal event at 520–505 Ma led to local resetting of the Th–U–Pb systematics in some monazites. Ages of 964–921 Ma obtained from metapelitic granulites constituting the oldest lithological component imply that the Chilka Lake area was involved in the global Grenvillean orogenesis, which was the fabric-defining tectonothermal event in most parts of the Eastern Ghats Belt. In combination with additional data from these authors and published data from other domains of the Eastern Ghats Belt, these results indicate that the post-Grenvillean evolution of the Eastern Ghats Belt is characterized by a sequence of Neoproterozoic tectonothermal events between 792 and 662 Ma and a Pan-African thermal event at 520–505 Ma. It further implies slow cooling of the entire granulite terrain. In view of appreciably different metamorphic conditions between the low-grade Proterozoic supracrustal cover of the Archean cratons (East-Dharwar and Bastar) and the neighbouring Proterozoic granulites of the Eastern Ghats Belt, it is suggested that final thrusting of the Eastern Ghats Belt over the Archean forelands took place in Early Phanerozoic time.