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Rock System in India: Archaean, Purana, Dravidian & Aryan

India's Gondwana, Archean, and Cuddapah rock formations

India’s Gondwana, Archean, and Cuddapah rock formations

Rock System in India: Based on radiometric dating and information about ancient life preserved in rock layers, the geological time scale is a compendium of the Earth’s geological history.

The Geological Survey of India officially classified the Indian rock system into four rock systems based on the country’s complex and diverse geological history.

The following categories are used to categorize the Indian rock system:

  • Archaean rock system
  • Dravidian rock system
  • Aryan rock system
  • Purana rock system

Archaean Rock System:

  • The Archaean rock system is also known as Pre- Cambrian rocks. 
  • It is the oldest rock system.
  • They are Archaean Gneisses and Archaean Schists which are formed nearly 4 billion years ago. 
  • They are formed during the pre-Cambrian era by the cooling and solidification of the upper surface of Earth’s crust.
  • They are azoic, which means they are formed when magma underneath the Earth’s surface solidified and has no fuel.
  • They are also faulted and generally have a well-defined foliated structure which means they are crystalline and form thin sheets. 
  • This type of rock is found in Karnataka, Tamil Nadu, Madhya Pradesh, Orrisa, Southern -eastern part of Rajasthan, and the Chhotanagpur plateau of Jharkhand. 
  • They contain gneisses (which range from granite to gabbro) and schists (crystalline rocks such as mica, talc, etc.). 
  • These rocks have metallic and non-metallic minerals like copper, tin, graphite, lead, zinc, etc.
  • They are also known as “Basement complexes” as they are the oldest and form the base for new layers.   
  • In this, volcanic rocks are also found inside when going in deep which results in plutonic intrusions.

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Dharwar system:
  • These are formed from 4 Billion years to 1 Billion years ago. 
  • They are the oldest metamorphosed rocks and the first metamorphosis sedimentary rocks in India.
  • It was named so because they were first studied in the Sarwar region of Karnataka. 
  • These are highly metamorphosed sedimentary rock system which was formed due to the metamorphosis of sediments of Archaean gneisses and schists.
  • They occur in scattered patches in parts of Karnataka, Tamil Nadu, Meghalaya Plateau, Garhwal and Kumaon, the Himalayan region, and Aravalis.  
  • They are economically important rocks as they have valuable minerals like high-grade iron ore, lead, gold, zinc, etc. 
  • They do not have fossils.
Purana Rock System:

The Cuddapah system and the Vindhyan system are the two divisions of the Purana rock system. Rock System in India, the term “Purana” was used in place of the Proterozoic period in history

Cuddapah Rock system:
  • The non-fossiliferous clay, slates, sandstones, and limestones accumulated in the depression between two-fold mountains which are known as synclinal basins.
  • This type of rock contains ore of iron, cobalt, nickel, manganese, etc.
  • They also have a large accumulation of building-purpose cement-grade limestones and quartzites. 
  • The offshoot was observed in the Cuddapah districts of Andhra Pradesh.
  • The Cuddapah system is segregated from the Dharwar system by a great unconformity.
  • It is found in some parts of Southern India in the Kurnool district of Andhra Pradesh, the Southern part of Chhattisgarh covering Bastar, Durg, Raipur, some parts of Orrisa, and along with the main axis of the Aravalli range.  
Vindhya Rock System:
  • This type of rock system is also ancient or old sedimentary rocks that are superimposed on the Archaean rock base and derived its name from the Vindhya mountains. 
  • They have a thickness of over 4,000m and have a stratified formation of sandstones, shales, and limestones.
  • They are spread from Sasaram and Rohtas in Bihar to Chittaurgarh in Rajasthan except for the central tract in Bundelkhand. Most of the area of this is covered with the Deccan trap.
  • The recognition of fossils is negligible, only traces of a few animal and plant life was found.
  • The Vidhayan system is further divided into two systems: the lower Vidhayan system and the upper Vindhayan system. 
  • The former is marine in origin, mostly calcareous in nature while the latter formed from 1000- 600 million years from now, fluviatile in origin and lies in undistributed horizontal strata. 
  • They both are separated by unconformity which is dominant in the north but less visible in southern areas of Mewar and the Son valley.
  • Vindhya system does not have metalliferous minerals but has ornamental stones, durable free stones, etc.
  • This rock system hove diamond-bearing regions from which Golconda and Panna diamonds are mined.
Dravidian Rock System:
  • This is also known as the carboniferous rock system and formed during the Paleozoic era, i.e., from 600- 300 million years ago.
  • They are not much abundant in India. 
  • They have plentiful fossils and the beginning of coal formation can be seen in this period. The quality of carboniferous coal is high.
  • They are found in extra- Peninsular regions of the Himalayas and the Gangetic plains. 
  • This type of rock system comprises limestones, shale, and quartzite, and Mount Everest is formed of upper Carboniferous limestones.
  • Most of the coal is not from the Carboniferous period, which is found in India.
  • The meaning of Carboniferous in geology is coal-bearing.

Aryan Rock System

The Aryan rock system in India has the following four systems:

  • Gondwana rock system
  • Jurassic Rock System
  • Cretaceous system/ Deccan Trap
  • Tertiary rock system
Gondwana Rock System:
  • These are found mainly in Ranigunj, and Jharia regions of Jharkhand, Damodar valley, Pench valley in Chhattisgarh, and Madhya Pradesh. 
  • They are divided into Damuda and Panchet, which are a series of rocks. 
  • They are called so after the name of the Gondwana tribe (indigenous people especially residing in Telangana and Andhra Pradesh region). 
  • In this type of rock system, you found metallic minerals like iron, manganese, uranium, etc. other than coal.  
  • They are also sedimentary deposits that were collected in synclinal troughs on an older plateau surface. They have low carbon content as it is much younger than Carboniferous coal.
  • These rocks have nearly 98% of India’s coal reserve
Jurassic Rock System:
  • During the latter part of Jurrasic when the sea level rises as compared to land and the shoreline move towards the ground or land it results in a flood. In geology, this phenomenon is called marine transgression. 
  • This gives rise to a thick series of shallow-water deposits in Rajasthan and Kutch. Between the Guntur and Rajamundry, another transgression on the east coast of the Peninsula.
  • In Kuchchh, coral limestone, shales, and conglomerates are found. 

Deccan trap or Cretaceous Rock System

  • These are formed by the flow of magma over the solidified rock system in layers. 
  • Deccan trap gets rises due to volcanic outbursts over a major area of Peninsular India from the end of the Cretaceous till the beginning of the Eocene. 
  • The meaning of trap is “stair” or “step” in Swedish and is called due to the deposition of the volcanic outburst which has a flat top and steep sides.
  • The size of the Deccan trap is reduced by almost half of its original size due to weathering and denudation. 
  • It is mainly found in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau, and Northern Karnataka and presently covers nearly 5 lakh sq. Km.
  • The thickness of the Deccan trap is reduced in the South as compared to the West and only 150 meters in the eastern limit.
  • Regur, which is black soil, is formed due to the weathering of these rocks for a long time.
  • The Deccan trap is also divided into three categories: upper trap, middle trap, and lower trap. 
Tertiary rock system:
  • The formation of this type of rock system occurs from 60 to 7 million years ago.
  • It is the most noteworthy period in India’s geological history as the Himalayas were born and recent forms came in this period.

What is the Classification of Rocks?

Sure, I can help you summarize the information in a bullet point format:

Igneous Rocks:
  • Intrusive Igneous Rocks:
    • Form below the Earth’s surface as magma cools slowly.
    • Result in large crystals.
    • Examples include granite, diorite, and pegmatite.
  • Extrusive Igneous Rocks:
    • Form on the Earth’s surface as lava cools rapidly.
    • Result in small crystals or amorphous glass.
    • Examples include tuff, basalt, and pumice.
Sedimentary Rocks:
  • Clastic Sedimentary Rocks:
    • Form from weathered debris and sediment accumulation.
    • Examples include sandstone and siltstone.
  • Chemical Sedimentary Rocks:
    • Form from the precipitation of dissolved elements in a solution.
    • Examples include iron ore and limestones.
  • Organic Sedimentary Rocks:
    • Form from the accumulation of plant and animal debris.
    • Examples include coal and some dolomites.
Metamorphic Rocks:
  • Foliated Metamorphic Rocks:
    • Develop layers due to heat and pressure.
    • Examples include gneiss and phyllite.
  • Non-Foliated Metamorphic Rocks:
    • Lack distinct layers.
    • Examples include quartzite and marble.

Common Elements in Earth’s Crust:

  • Silicon and oxygen are the most prevalent elements in the Earth’s crust, composing the majority of rocks.

What is the Formation of Rocks?

Sedimentary Rocks:
  1. Sedimentary rocks comprise fragments of other rocks or organic matter.
  2. They can be categorized into three types: clastic, biological, and chemical sedimentary rocks.
  3. Clastic sedimentary rocks, like sandstone, result from the accumulation of rock fragments and debris.
  4. Organic sedimentary rocks, such as coal, form from the compression of organic materials like plants, shells, and bones.
Metamorphic Rocks:
  1. Metamorphic rocks undergo transformation due to extreme heat or pressure.
  2. There are two main types: foliated and non-foliated.
  3. Foliated rocks form when minerals align in layers as a result of pressure, often containing flat or elongated minerals like mica or hornblende.
  4. Non-foliated rocks lack distinct layering and have a more uniform texture.
Igneous Rocks:
  1. Igneous rocks originate from the cooling and hardening of molten materials.
  2. They can be created through different processes.
  3. Intrusive or plutonic igneous rocks form deep within the Earth’s crust.
  4. Extrusive igneous rocks, also known as volcanic igneous rocks, develop on or above the Earth’s crust, often through volcanic eruptions.

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