In this article, we will discuss Geological Structure and Formation of India (Continued). So, let’s get started.
Dharwar System (Proterozoic Formations)
This geological time extends from 2500 million years ago to 1800 million years ago. These are the first metamorphosed sedimentary rock systems known as the Dharwar System in the Indian Geological Time Scale, as they were studied for the first time in the Dharwar district of Karnataka. They are composed largely of igneous debris, schists and gneisses. The Dharwar rocks occur in scattered patches in (i) Dharwar and Bellary districts of Karnataka and extend up to the Nilgiris and Madurai districts of Tamil Nadu, (ii) Central and eastern part of the Chotanagpur Plateau, Meghalaya Plateau and Mikir Hills, and (iii) the Aravallis, Rialo (Delhi series), from Delhi to the south of Alwar and the Himalayan region.
The Dharwar rocks are rich in minerals like iron ore, manganese, lead, zinc, gold, silver, dolomite, mica, copper, tungsten, nickel, precious stones and building materials.
The Cuddapah System (The Purana Group)
The Cuddapah system is made of shales, slates, limestone. and quartzite. The rocks are generally without fossils because there was no origin of species during their formation. The Cuddapah formations, named after the district of Cuddapah in Andhra pradesh, are sedimentary-metamorphic formations. The Cuddapah system occurs in the (i) Cuddapah and Kurnool districts of Andhra Pradesh, (ii) Chhattisgarh, (iii) Rajasthan-Delhi to the south of Alwar, and (iv) the Lesser Himalayas in the extra-Peninsular region. At places the Cuddapah formations are 6,000 m in thickness. The enormous thickness of these rocks indicates the sinking of beds of the basin with growing sedimentation.
The Vindhvan system
The Vindhvan system derives its name from the Vindhyan Mountain. This mountain forms a
dividing line between the Ganga Plain and the Deccan Plateau. The system covers an extensive area of 103.600 sq km from Chittorgarh in Rajasthan to Sasaram in Bihar. It has enormous sedimentary deposits and at places their depth is more than 4000 m. In some tracts, the Vindhyan rocks are buried under Deccan lava. The Great Boundary Fault (GBF) separates the Vindhyan System from the Aravallis for a distance of about eight hundred km.
The Vindhvan system is well known for red-sandstone, sandstone, building material, ornamental stone, conglomerates diamondiferous and raw materials for cement, lime, glass and chemical industries In certain places these rocks yield inferior quality of iron ore and manganese. The well known diamond mines of Panna and Golconda lie in the Vindhyan system. The historical buildings of Qutab Minar, Humayun’s Tomb, Fatehpur Sikri, Agra Fort, Red Fort, Jama Masjid, Birla Mandir, the Buddhist Stupa of Sanchi, etc., have been constructed from the red sandstone obtained from the Vindhyan Ranges. Coarser sandstones have been used as grindstones and millstones.
The principle rocks of the Cuddapah system are sandstones, shales, limestone, quartzites slates, inferior quality of iron-ore, manganese ore, asbestos, copper, nickel, cobalt (Delhi System), marble, jasper, building material and stones for interior decoration. The metallic contents in the ores of Cuddapah rocks are, however, low and at places uneconomical for extraction.
