ARAVALLI AND DELHI FOLD BELTS

In western India, a 700 km long mountain range known as Aravalli Mountain contains record of two orogenic movements, an early Aravalli orogeny, early Proterozoic in age and affecting the rocks deposited in an epicontinental sea with volcanics at the base and clastics at the top. The second orogeny is Middle Proterozoic in age affects both the older Aravalli rocks, already deformed and another group called Delhi that is mostly volcanic, carbonates and some clastics. Though the Delhi rocks occupy the entire mountain range, the name derives from the older rocks. Inset is photograph of Dr A M Heron, whose pioneering work in this belt and the solid map he produced are difficult to refute even today. The rocks of the Aravalli Supergroup show only greenschist facies of metamorphic grade while those of the Delhi Supergroup are highly metamorphosed to amphiblite assemblages with sporadic occurrences of granulite facies of rocks as at Sandmata.