Archaean Rock System of India
Geography › India: Location, Geology and the Himalayas · Topic 13.3
The Archaean rock system is the oldest geological system of India, made of crystalline gneisses and schists that form the basement complex of the Peninsula, with the Dharwar system, the oldest metamorphosed sedimentary rocks, above it. These are the source of India's iron ore, manganese, copper and gold. The younger Purana system, with the Cuddapah and Vindhyan rocks, lies above and carries limestone and building stone.
5 min read · UPSC Prelims · Geography · India: Location, Geology and the Himalayas
At a Glance
- Age Archaean: more than 2.5 billion years
- Rocks Gneiss, schist, granite
- Dharwar Metamorphosed sediments; iron, manganese, gold
- Purana Cuddapah and Vindhyan; 600 to 1,400 million years
- Fossils Absent (azoic)
- Exam link UPSC Prelims, Geography: India: Location, Geology and the Himalayas
Where Does It Fit?
This is the third topic of the macro on India’s location, geology and the Himalayas. The previous topic described the physical divisions, and this one begins the study of the rock systems with the oldest. The next topic covers the Dravidian and Aryan rock systems. Previous topic: Major Physical Divisions of India. Next topic: Dravidian and Aryan Rock Systems of India.
How Are the Rocks of India Classified?
In short: Indian rocks are grouped by age into four systems: Archaean, Purana, Dravidian and Aryan.
| System | Approximate age | Rocks and region |
|---|---|---|
| Archaean | Oldest, from the formation of the crust to about 2.5 billion years ago | Gneisses, schists and granites; the basement of the Peninsula; includes the Dharwar system |
| Purana | About 600 to 1,400 million years | Cuddapah and Vindhyan systems; sedimentary |
| Dravidian | Palaeozoic, about 600 to 300 million years | Fossil-bearing sedimentary rocks, mainly in the Himalayas |
| Aryan | Upper Carboniferous to the present | Gondwana, Jurassic, Deccan Trap and Tertiary systems |
The geological time scale underlies this classification, with the Precambrian covering more than 85 per cent of Earth’s history. The Dravidian and Aryan systems are covered in Dravidian and Aryan Rock Systems of India. The names are only a convenient classification, and, for instance, the Dravidian system is not found in southern India.
What Is the Archaean Rock System?
- Gneisses and schists: the oldest rocks, formed when the molten surface of the young Earth cooled and solidified, then altered by heat and pressure. Gneiss varies in composition from granite to gabbro, and schist is a crystalline rock with mica, talc, hornblende and chlorite. Many text sources give an age of about 4 billion years, but modern dating of the oldest Indian rocks, such as the Singhbhum and Dharwar cratons, gives ages of about 3.3 to 3.6 billion years.
- The basement complex: they are called the basement complex, because they form the floor on which all later rocks lie. They are crystalline, foliated, in thin sheets, and do not contain fossils, because they were formed before life existed in a form that could be preserved. They cover most of the Peninsula, in Karnataka, Tamil Nadu, Andhra Pradesh, Odisha, Jharkhand, Chhattisgarh and Rajasthan.
- Cratons: the ancient, stable cores of the Indian shield are the Dharwar, Bastar, Singhbhum, Bundelkhand and Aravalli cratons, as in Peninsular Plateau and Minor Plateaus.
What Are the Dharwar and Purana Systems?
| System | Description | Resources |
|---|---|---|
| Dharwar system | The oldest metamorphosed sedimentary rocks of India, formed from the sediments of the older gneisses and schists; named after the Dharwar district of Karnataka; spread over Karnataka, the Aravallis, Chotanagpur and Odisha; about 1 to 4 billion years old in the older classification | The most important rocks economically: high-grade iron ore, manganese, copper, lead, gold, chromite; the Kolar and Hutti gold fields; Bellary-Hospet and Singhbhum iron ores |
| Cuddapah system | Unfossiliferous clay, slate, sandstone and limestone, deposited in synclinal basins and folded; best seen in the Cuddapah district of Andhra Pradesh | Iron, manganese, copper, cobalt, nickel, asbestos and cement-grade limestone |
| Vindhyan system | Ancient sedimentary rocks, up to about 4,000 m thick, lying on the Archaean base in Madhya Pradesh, Rajasthan, Uttar Pradesh and Bihar; mostly without fossils; partly covered by the Deccan Traps | Few metals; diamond-bearing zones such as Panna; sandstone, limestone, glass sand and building stones, used in structures such as the Sanchi stupa and the Red Fort |
The Archaean and Dharwar areas, especially Chotanagpur and the Dharwar craton, are the mineral heartland of India, and the large industries of Jharkhand, Odisha, Chhattisgarh and Karnataka grew on them, as in Iron Ore – Types and Distribution. The Kolar gold fields in Karnataka, once among the deepest gold mines in the world, were closed in 2001 after the ore was depleted. As an analytical point, these old rocks illustrate why the Peninsula is rich in minerals and poor in fossil fuels apart from the Gondwana coal: the great age and the metamorphism concentrated metals, but the absence of young sedimentary basins limited oil and gas.
Why Is This Topic Important?
- Facts System names and minerals asked
- Economy Mineral belts
- Concepts Basement complex and craton
What Came Next?
The next topic describes the Dravidian and Aryan rock systems. Next topic: Dravidian and Aryan Rock Systems of India.
Key People and Terms
- Basement complex Oldest crystalline floor
- Gneiss Banded metamorphic rock
- Schist Foliated crystalline rock
- Craton Ancient stable core of a continent
- Unfossiliferous Without fossils
- Syncline Downfold of rock layers
Exam Corner
Points to Remember
- Archaean rocks are unfossiliferous.
- The Dharwar system is the richest in metals.
- Cuddapah is in Andhra Pradesh.
- Vindhyan rocks yield building stone and diamonds.
- Purana: Cuddapah and Vindhyan.
Do Not Confuse With
- Archaean and Dharwar Igneous-metamorphic basement versus metamorphosed sediments
- Cuddapah and Vindhyan Metal-bearing versus mostly building stone
- Gneiss and schist Banded versus platy
Memory Hook
Basement first, Dharwar carries the metals, Cuddapah folds, Vindhyan builds and shines.
Mains Angle
Questions link geology with minerals. These points add depth.
- Age Oldest crust
- Minerals Dharwar belts
- Gap Few young basins
A Question You May Face
An original practice question, not a past paper question.
“Describe the Archaean and Dharwar rock systems of India and explain their economic importance.”
How to Answer
- Archaean Basement and cratons.
- Dharwar Metamorphosed sediments.
- Purana Cuddapah and Vindhyan.
- Economy Minerals and stone.
GS Relevance
Frequently Asked Questions
What is the Archaean rock system?
The Archaean rock system consists of the oldest rocks of India, mainly gneisses, schists and granites, formed by the cooling of the molten early crust. They form the basement complex of the Peninsula, do not contain fossils, are crystalline and foliated, and cover large parts of southern and eastern India.
Why is the Dharwar system economically important?
The Dharwar system consists of metamorphosed sedimentary rocks, and it is rich in metallic minerals such as high-grade iron ore, manganese, copper, lead, chromite and gold. The iron ore of Karnataka, Odisha and Jharkhand and the gold of Kolar and Hutti are found in it.
What is the Cuddapah system?
The Cuddapah system is a Purana rock system of unfossiliferous slates, sandstones, clays and limestones, deposited in synclinal basins and then folded. It is best seen in the Cuddapah district of Andhra Pradesh and has iron, manganese, copper, cobalt, nickel and cement-grade limestone.
What is the Vindhyan system?
The Vindhyan system is a thick sequence of ancient sedimentary rocks, up to about 4,000 metres, in central and northern India, named after the Vindhya hills. It has few metals but provides sandstone, limestone, glass sand, and the diamond-bearing area around Panna.
What is the basement complex?
The basement complex is the oldest group of crystalline rocks, mainly Archaean gneisses and granites, which form the foundation on which all younger rocks of the Peninsula were deposited. It is exposed over large parts of the Peninsular Plateau because the overlying rocks have been eroded away.
PYQ Practice — Statement Analysis
1 Archaean rocks contain abundant fossils.
They are unfossiliferous.
2 The Dharwar system is named after a district of Karnataka.
It is rich in iron ore and gold.
3 The Cuddapah system is best exposed in Andhra Pradesh.
The name comes from Cuddapah district.
4 The Vindhyan system is rich in metallic minerals.
It is mostly known for building stone and limestone.
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