GEOLOGICAL STRUCTURE OF INDIA

INTRODUCTION

• The geology of India is extremely diverse.
• Different parts of India contain rocks belonging to different geological periods.
• Some rocks date back to the Eoarchean era, while some deposits are very recent alluvium.
• Geological structure decides:
  - Soil characteristics
  - Mineral availability
  - Type of agriculture
  - Industrial development
  - Settlement and culture

IMPORTANT FACTS ABOUT INDIA (QUICK REVISION)

• Geographical location: North-Eastern Hemisphere
• Area: 32,87,263 sq km
• Latitudinal extent: 8°4’ N to 37°6’ N
• Longitudinal extent: 68°7’ E to 97°25’ E
• Standard Meridian of India: 82.5° E (IST = GMT + 5:30)
• North-South length: 3214 km
• East-West breadth: 2933 km
• Land boundary: 15,106.7 km
• Coastline (including islands): about 7515 km
• Share in world area: about 2.42%
• Share in world population: about 17.5%
• Population density: about 382 persons per sq km
• Number of States: 28
• Number of Union Territories: 8
• India’s rank in world:
  - Area: 7th
  - Population: 2nd
• Sex ratio: 943 females per 1000 males
• Urban population: about 31.2%
• Climate: Monsoon type
• Major ports: 13

INDIA: PHYSICAL OVERVIEW AND IMPORTANT LINES

• 82.5° E longitude passes near Naini (Prayagraj) and is the basis of Indian Standard Time.
• States through which IST passes:
  - Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Odisha, Andhra Pradesh
• Tropic of Cancer passes through 8 states:
  - Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura, Mizoram
• India is the only country after which an ocean is named (Indian Ocean).
• Neighbours:
  - Pakistan, Afghanistan, China, Nepal, Bhutan, Myanmar, Bangladesh
• Palk Strait separates India from Sri Lanka.
• India’s longest international border is with Bangladesh (about 4096.7 km).
• Southernmost point of India: Indira Point (Great Nicobar Island)
• Important latitude separations:
  - 6°: Indira Point and Indonesia
  - 8°: Minicoy and Maldives
  - 9°: Kavaratti and Minicoy
  - 10°: Andaman and Nicobar Islands

GEOLOGICAL DIVISIONS OF INDIA

The geological structure of India can be studied under three major units:
• The Peninsular Plateau
• The Great Himalayas of the North
• The Great North Indian Plains

SIGNIFICANCE OF GEOLOGICAL STRUCTURE

• Determines:
  - Soil types
  - Mineral resources
  - Industrial regions
  - Agricultural patterns
  - Economic activities
• Hence, geology forms the base of physical and economic geography of India.

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PENINSULAR PLATEAU
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• It is the oldest landmass of India.
• Composed mainly of:
  - Igneous rocks
  - Metamorphic rocks
• Most rocks belong to very ancient geological periods.
• It is a stable and rigid block.

MAIN ROCK SYSTEMS OF PENINSULAR PLATEAU

1. ARCHEAN ROCKS

• Oldest primary rocks of India.
• Highly metamorphosed into:
  - Gneiss
  - Schist
• Found in:
  - Central and southern parts of the Peninsular Plateau

2. DHARWAR ROCKS

• Formed from erosion and deposition of Archean rocks.
• Highly metamorphosed.
• Fossils are absent.
• Found in:
  - Dharwar and Bellary districts of Karnataka
  - Aravalli Range
  - Chotanagpur Plateau
• Important minerals:
  - Iron ore
  - Copper
  - Gold

3. CUDDAPAH ROCKS

• Formed from erosion and deposition of Dharwar rocks.
• Less metamorphosed compared to Dharwar.
• Fossils absent.
• Found in:
  - Krishna Valley
  - Nallamalai Hills

4. VINDHYAN ROCKS

• Formed after Cuddapah rocks.
• Spread from:
  - Chittorgarh (Rajasthan) to Sasaram (Bihar)
• Mainly composed of:
  - Sandstone
• Economic importance:
  - Poor in metallic minerals
  - Rich in limestone, ornamental stones and glass-making sand

5. GONDWANA ROCKS

• Composed of:
  - Sandstone
  - Shale
  - Clay
• Very important for:
  - Coal deposits
• Found in river valleys of:
  - Damodar
  - Mahanadi
  - Godavari and their tributaries

6. DECCAN TRAP

• Formed by basaltic lava flows.
• Lava spread in layers.
• Creates step-like structures called “Trap” (meaning step).
• Spread over:
  - Maharashtra
  - Gujarat
  - Madhya Pradesh
  - Chhattisgarh
  - Telangana
  - Andhra Pradesh
  - Karnataka
• Forms black soil (Regur soil) which is very good for cotton cultivation.

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GREAT HIMALAYAS OF THE NORTH
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• The Himalayas are geologically young fold mountains.
• Recent studies show:
  - Base is made of gneiss and granite
  - Upper layers are sedimentary and fossiliferous

FORMATION OF HIMALAYAS (PLATE TECTONIC THEORY)

• About 70 million years ago:
  - Indian Plate started moving northwards towards Eurasian Plate.
• Between them existed the Tethys Sea.
• Due to plate movement:
  - Tethys Sea began to shrink.
• Indian Plate was denser:
  - It subducted under Eurasian Plate.
• This caused:
  - Compression and folding of sediments.
• Folding occurred in three main phases:
  - Resulted in three parallel Himalayan ranges.
• Even today:
  - Himalayas are rising slowly
  - At the same time, erosion and denudation continue.

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GREAT NORTH INDIAN PLAINS
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• It is the most recent geological formation of India.
• Formed by:
  - Weathering
  - Erosion
  - Deposition by rivers
• Built by:
  - Indus, Ganga, Brahmaputra and their tributaries
• Two types of alluvium:
  - Bhangar: Old alluvium
  - Khadar: New alluvium
• This region is:
  - Extremely fertile
  - Densely populated
  - Agricultural heartland of India

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CONCLUSION

• India’s geological structure explains:
  - Distribution of mountains, plateaus and plains
  - Availability of minerals and soil
  - Pattern of agriculture and industries
• Hence, understanding geology is fundamental for:
  - Physical geography
  - Economic geography
  - Environmental studies
  - Disaster management

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Subject: Geography

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