Eparchaic discordance
Coordinates: 13 ° 39 ′ 10 ″ N , 79 ° 21 ′ 0 ″ E
The Eparchaic Discordance is a significant discordance in the Tirumala Hills in the Indian state of Andhra Pradesh . It has been one of the national geological monuments of India since 2001 .
Geographical location and access
The geological monument (site 2 in the systematics of the Geological Survey of India ) follows the south and west limits of the Tirumala Hills and runs above the new access road from Tirupati to Tirumala . Along the road, it is 10 kilometers northwest of Tirupati at kilometer 12 of the Tirupati-Tirumala Ghat Road . The Tirumala Hills break off here along a rock wall towards the Tirupati Basin. The Eparchaic Discordance lies below the rock face, but is mostly covered by debris, rubble and dense vegetation. The Tirumala Hills reach heights of around 900 meters, while the basin is 150 meters above sea level.
Located above the monument, Tirumala is a pilgrimage site and made famous by the Venkateswara temple .
Tirupati at the foot of the Tirumala Hills can be reached both by rail and by public buses in Andhra Pradesh . The nearest airport is Renigunta, about 15 kilometers away, with flights to Chennai , Hyderabad and Bangalore .
geology
The Eparchaic Discordance represents a significant temporal break in the geological history of India. It follows the entire western edge of the Cuddapah Basin , whereby the age of the overlying layers can be subject to great temporal fluctuations. On the monument itself, the archaic basement of the eastern Dharwar kraton - the Peninsular Gneissic Complex (PGC) consisting of gneisses , granites and dolerite dykes - is discordant with the around 1600 million year old Nagari quartzites (also Bairenkonda quartzites or Cuddapah quartzites ) placed. These quartzites belong to the Proterozoic Cudappah supergroup in the Cudappah Basin, a sedimentary sequence of quartzites, sandstones , shale and limestone , predominantly 5,000 to 6,000 meters thick . The total thickness in the basin can swell up to 12,000 meters and also contain magmatites in the form of tunnels , storage tunnels and lava flows . Within the Cuddapah supergroup, the Nagari quartzites form the lowest formation of the 1200 meter thick Nallamalai group in the Nallamalai fold belt , a part of the Cuddapah basin. The Nallamalai group is then overlaid by the 500-meter-thick Kurnool group , which forms the stratigraphic closure in the basin.
The plateau-like Tirumala Hills form the extreme southeastern edge of the horn-shaped Cuddapah Basin belonging to the Purana Basin; its sediment thickness is, however, severely limited compared to the rest of the basin due to its peripheral location.
Age
The archaic age of the Peninsular Gneissic Complex is based on its last granitic intrusion phase through the Closepet granite , which was dated to 2530 to 2510 million years BP . In general, however, the PGC is assigned an age of 3300 to 2700 million years ( Paleo-Archean to Neo-Archean ). The age of Nagari quartzite is not available, so its age can only be estimated indirectly. This occurs through the intrusion of the 1584 million year BP old Vellaturu granite of the Calymmium on the eastern edge of the Nallamalai fold belt. Since the granite intrusion took place in the uppermost layers of the Nallamalai group, an age of around 1600 million years BP can be assumed for the Nagari quartzite, ie the quartzite was deposited at the turn of the Paleoproterozoic / Mesoproterozoic . The Eparchaic Discordance thus represents a hiatus of around 900 million years in the Tirumala Hills.
Picture gallery
Notice board on the Eparchaische Discordance
Waterfall in the Nagari quartzite at Kapilatheertham
Detail of the Nagari quartzite
Rock arch Silathoranam made from Nagari quartzite in the Tirumala Hills
Individual evidence
- ^ Geological Survey of India: Geological Monuments of India. Eparchaean Unconformity (Tirupati Tirumala Road) . 2001, p. 5-8, 95 .
- ↑ Jayananda, M., Martin, H., Peucat, JJ. and Mahabaleswar, B .: Late Archaean crust-mantle interactions: geochemistry of LREE enriched mantle derived magmas. Example of the Closepet batholith . In: Contrib. Mineral. Petrol . tape 119 , 1995, pp. 314-329 .
- ↑ Taylor, PN, Chadwick, B., Moorbath, S., Ramakrishanan, M. and Viswanathan, MN: Petrography, chemistry and isotopic ages of Peninsular gneisses, Dharwar acid volcanics and Chitradurga granites with special reference to Archaean evolution of Karnataka craton, southern India . In: Precambrian Research . tape 3 , 1984, pp. 349-375 .
- ↑ Saha, D. and Chakraborti, S .: Advective heat transfer and fabric development in a shallow crustal intrusiv granite - the case of Proterozoic Vellaturu granite, South India . In: Journal of Earth System Science . tape 116 , 2007, pp. 433-450 .