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GEOGRAPHY(Optional) for MAINS- (PAPER 2) L1 By ASHISH MALIK
ABOUT ME o ASHISH MALIK (B.E.Civil) o APPEARED FOR UPSC CSE MAINS TWICE (2016,2017) o GS FACULTY o STAR EDUCATOR@UNACADEMY o ONLINE CONTENT BUILDER o MOTIVATIONAL SPEAKER Follow me on UNACADEMY https://unacademy.com/user/AshishMalik-8996
STRUCTURE OF INDIA 1. THE ARCHAEAN FORMATIONS (PRE-CAMBRIAN) The term 'Archaean', introduced by J.D. Dana in 1782, refers to the oldest rocks of the Earth's crust. This division of geologic time scale from the formation of the Earth (about 4.6 billion years ago) to the beginning of the Cambrian Period of the Paleozoic Era (about 570 million years ago). The Precambrian time constitutes about 86.7% of the Earth's history. . The Archaean rocks are all azoic or un fossiliferous. They are thoroughly crystalline, extremely consorted and faulted, and practically devoid of any sediment. They are largely intruded by plutonic intrusions and generally have a well-defined foliated structure. These rocks are known as the basement complex or fundamental gneisses and cover two-thirds of Peninsular India.
In the Peninsular region, the Archaean rocks are known to be of three well-defined types: .(i) The Bengal Gneiss- occurs in the Eastern Ghats, Orissa (known as Khodoliles after Khond tribes, stretching over Manbhum and Hazaribagh districts of Jharkhand, Nellore district of Andhra Pradesh and Salem district of Tamil Nadu. It also occur in the Son Valley, Meghalaya Plateau and Mikir Hills. (ii) The Bundelkhand Gneiss- forms the second group of fundamental gneiss of the Archaean age. It occurs in Bundelkhand (U.P.), Baghelkhand (M.P.), Maharashtra, Rajasthan, Andhra Pradesh and Tamil Nadu. Its a coarse grained gneiss which looks like granite. (iii) The Nilgiri Gneiss- A bluish-grey to dark coloured rock, medium to coarse grained in texture. This is plutonic gneiss intruding into the other Archaean rock masses. It is widely found in South Arcot, Palni Hills, Shevaroy Hills and Nilgiri in Tamil Nadu, Nellore in Andhra Pradesh, Balasore in Orissa, Karnataka, Kerala, Malabar, Jharkhand, Chhattisgarh and Aravallis (Rajasthan) The Archaean rocks are the repositories of the mineral wealth of India. These rocks are rich in ferrous and non-ferrous minerals like iron ore, copper, manganese, mica, dolomite, lead, zinc, silver and gold.
2. DHARWAR SYSTEM (PROTEROZOIC FORMATIONS) This geologic time extends from 2500 million years ago to 1800 million years ago. The first metamorphosed sedimentary rock systems known as the Dharwar System in the Indian Geological Time Scale. In India, these rocks were studied for the first time in the Dharwar district of Karnataka. It composed largely of igneous debris, schists and gneisses. The Dharwar rocks occur in scattered patches in (i) Dharwar and Bellary districts of Kamataka and extend up to the Nilgiris and Madurai districts of Tamil Nadu, () Central and eastern parts of the Chotanagpur Plateau, Meghalaya Plateau and Mikir Hills, and (ii) the Aravallis, Rialo (Delhi series), from Delhi to the south of Alwar and the Himalayan region Dharwar rocks are highly metalliferous. They are rich in iron ore, manganese, lead, zinc, gold, silver, dolomite, mica, copper, tungsten, nickel, precious stones and building materials.
Some of the important series of the Dharwar System are: (a) Champion Series- Belonging to the Dharwarian System, the series has been named after the Champion reef in the Kolar Gold fields. Lying to the north-east of Mysore City and to the east of Bangalore, this series stretches in the Kolar and Raichur districts of Kamataka. Its gold mines are one of the deepest in the world, being more than 3.5 km in depth. (b) Champaner Series- an outlier of the Aravallis system in the vicinity of Vadodra. It consists of quartzites, conglomerates, phyllites, slates and marbles. An attractive green variety of marble is obtained from this series. (c) Closepet Series- Stretching over the Balaghat and Chhindwara. districts of Madhya Pradesh, it is a Dharwarian formation. It consists of quartzite, copper pyrite, and magniferous rocks. The Malanjkhand Copper Plant gets its ore from the Closepet series. .(d) Chilpi Series- occupies parts of Balaghat and Chhindwara districts of Madhya Pradesh. It consists of grit, phyllite, quartzites, green stones and magniferous rocks. (e) Iron-Ore Series- occurs in Singhbhum, Bonai, Mayurbhanj and Keonjhar in the form of a range.lt is about 65 kilometres in length and reserves about three thousand million tons of iron-ore.
Some of the important series of the Dharwar System are: . (f) Khondolite Series- occupies a large area in the Eastern Ghats from the northern extremity to the valley of Krishna. The principal rock types in this series are khondolites, kodurites, charnockites and gneisses. (g) Rialo Series- known as the Delhi series, it extends from Delhi (Majnu-Ka-Tila) to Alwar, Rajasthan in a north-east to south-west direction. It is rich in marbles. The Makrana, and Bhagwanpur known for high quality of marble belong to this series .(h) Sakoli Series- Stretching over Jabalpur and Rewa districts, this series belongs to the Dharwarian formation. It is rich in mica, dolomite, schist and marble. The marble of this series is of superior quality. . (i) Sausar series- spreads over Nagpur, Bhandara districts of Maharashtra, and Chindwara district of Madhya Pradesh. It belongs to the Dharwarian group and is rich in quartzite, mica ,schist, marble and magniferous rocks.