Metamorphic chronology of the Precambrian provinces of South India

Abstract

There are three Precambrian provinces in southern India — the Dharwars (metavolcanics, metasediments, charnockites and granites), the Eastern Ghats (metasediments, charnockites and granites), and the Cuddapahs (essentially flat-lying continental sediments disturbed at the margins) — with chronostratigraphic histories dovetailing into one another. The Dharwars bear the impress of three episodes (about 3000 m.y., 2600–2300 m.y., and about 2000 m.y.) of folding, metamorphism, and emplacement of granites, the second being the most important. The pelitic sediments deposited in the Eastern Ghats geosyncline during the post-Dharwar times (upper limit, 2600 m.y.) were later folded and metamorphosed about 1600 m.y. ago into garnet-sillimanite-graphite gneisses (khondalites). Important deposits of mica pegmatites developed during this episode. Charnockites and granites associated with the Eastern Ghats were emplaced 1520–1300 m.y. ago. The Eastern Ghats rocks were subsequently cross-folded and metamorphosed about 500 m.y. ago. The sedimentation in the Cuddapah Basin was initiated sometime after the Eastern Ghats orogeny (1600 m.y. ago) but before 1160 m.y. ago. The Cuddapahs were subjected to regional metamorphism about 500 m.y. ago.