India Geological Structure

• The land of India is characterized by great diversity in its physical features. The North has a vast expanse of rugged topography consisting of a series of mountain ranges with varied peaks, beautiful valleys, and deep gorges.
• The South consists of stable tableland with highly dissected plateaus and denuded rocks. In between these two, lies the North-Indian plain.

Introduction

• India boasts a vast geographical expanse, stretching from the towering Himalayas in the North to the sun-soaked coastal villages in the South, encompassing humid tropical forests on the South-West coast, the fertile Brahmaputra valley in the East, and the arid Thar desert in the West.
• Situated entirely in the Northern Hemisphere, the mainland spans between 8°4' N and 37°6' N latitudes and 68°7' E and 97°25' E longitudes. The country measures approximately 3,214 km between the North and South extreme latitudes and about 2,933 km between the East and West extreme latitudes.
• India shares its borders with Pakistan, Bangladesh, Nepal, Maldives, Bhutan, Sri Lanka, and even Afghanistan, forming a land frontier extending about 15,200 km. The total length of the coastline, including the mainland, Lakshadweep Islands, and Andaman and Nicobar Islands, amounts to 7,516.6 km.
• Indian Standard Time (IST) is calculated based on the 82.5° E longitude, passing near Allahabad. It stands 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).

Geological Composition of India

• The geological structure, encompassing the organization and deposition of rocks within the Earth's crust, significantly influences the land's relief and soil characteristics. 
• Additionally, it provides insights into the extensive mineral resources concealed beneath the Earth's surface. 
• While certain rocks display significant deformation and metamorphism, others represent recently deposited alluvium awaiting diagenesis.
• India's geological evolution traces back to the split of Pangea into two distinct continents: Laurasia (Angaraland) and Gondwanaland. India was originally part of the Gondwanaland Rock System. Laurasia constituted the contemporary continents of North America (Greenland), Europe, and Asia. Meanwhile, Gondwanaland comprised the current landmasses of Antarctica, Australia, Africa, South America, and Madagascar.

Time Scale of Indian Geological Structure

Classification of Indian Rocks

• Indian rocks can be divided into the following categories based on their formation in different periods of the Geological Time Scale (GTS)

Archaean Group

The rocks of the Archaean group are divided into two classes.

The Archaean Rock System

•  These are the oldest rocks of the Earth crust. They have been found at the bottom of the stratified (sedimentary) deposits in all countries of the world. These are also called as pre-Cambrian rocks.
• They are often called as the fundamental complex or the basement complex. They form the foundation of all ancient plateaus and core of all folded mountain ranges of the world, including Great Himalayas.
• These rocks have lost their fundamental structure due to undergoing excessive transformation over the years. Now, these are Gneiss and Schist type of rocks.
• The majority of the Indian Peninsular comprises Archaean rocks, classified into three types: Bengal Gneiss, Bundelkhand Gneiss, and Nilgiri Gneiss. 
• These rocks, located in various regions such as Odisha, Madhya Pradesh, Chhattisgarh, Chota Nagpur plateau, Meghalaya plateau, Bundelkhand, and extending from North of Vadodra to the Aravallis of Rajasthan and the entire length of the Himalayas (except Sikkim), form a crucial repository of India's mineral wealth.

Dharwar Rock System:

• Originating in the district of Dharwar in Karnataka, these ancient metamorphosed sedimentary rocks lack fossils.
• Found in various areas like Karnataka, Visakhapatnam, Gujarat, and the Aravalli ranges, they consist of hornblende, schist, quartzite, slates, and dolomite.
• Highly metalliferous, these rocks house minerals such as iron-ore, manganese, lead, zinc, gold, silver, mica, copper, precious stones, and building materials.
• Locations include Bellary, Mysore, Balaghat, Ladakh, Zaskar, Kumaon mountain ranges, Chota Nagpur plateau, Chhattisgarh, Odisha, Rajasthan, and Meghalaya plateau.

Purana Group:

Cuddapah Rock System:

• Formed through the erosion and deposition of Dharwar rocks 1400-600 million years ago.
• Predominantly found in Cuddapah district (Andhra Pradesh), Kurnool district, Chhattisgarh, Singhbhum (Jharkhand), Kalahandi, Keonjhar (Odisha), and Aravallis.
• Rich in iron, copper, manganese, cement, grade limestone, cobalt, nickel, asbestos, jasper, and quartzites.
• Known for low metallic contents in ores, some uneconomical for extraction.
• Rajasthan's Cuddapah rocks are also known as Delhi Ridge, hosting diamonds and gold.

Vindhyan Rock System:

• Named after the Vindhyan mountain, formed by the deposition of river valleys and shallow oceans.
• Acts as a dividing line between the Gangetic plains and the Deccan plateau, extending from Sasaram to Chittorgarh.
• Found in Bastar, Kaimur ranges, Chittorgarh, Bhima valley (Karnataka), and Kurnool district (Andhra Pradesh).
• Rich in durable stones, flagstone, ornamental stones, diamondiferous areas (Panna and Golconda), limestone, pure glass-making sand, red sandstone, sandstone, building materials, and raw materials for cement and chemical industries.
• Notable structures like Sanchi Stupa, Red Fort, Jama Masjid, Fatehpur Sikri, etc., were built using red sandstone.

The Dravidian Group (Palaeozoic: 600-300 Million Years Age) 

• The Dravidian Group (Palaeozoic: 600-300 Million Years Age) comprises various rock systems with distinct characteristics.
• Cambrian Rocks: Best developed in the North-West Himalayas, Spiti Valley, Kullu, Lahaul (Himachal Pradesh), Baramulla (Kashmir), and Kumaon Hills (Uttarakhand).
  • Main rocks include sandstone, shales, and dolomite.
• Ordovician Rocks: Developed in Spiti valley, Lidder valley, Kumaon region.
  • Main rocks: Quartzite, sandstone, grits, and limestones.
• Devonian Rocks: Developed in Spiti Valley and Kumaon.
  • Main rock: Quartzite.
• Carboniferous Rocks: Developed in Spiti valley, Kashmir, Shimla, Pir-Panjal, Kumaon, Chota Nagpur plateau, and Chhattisgarh.
  • Main rocks include sandstone, limestone, clay, shale, and coal.

The Aryan Group

The Aryan Group, from the upper Carboniferous period to the present times, is characterized by five rock systems.

Gondwana Rock System:

•  Formed during upper Carboniferous and Jurassic period.
• Discovered in Gond region of Madhya Pradesh, with sandstones, shales, clay, and deposits of iron-ore, copper, uranium, antimony, sandstone, slate, and conglomerates.
• Found in Damodar valley, Mahanadi valley, along Godavari, and in the Himalayas (Kashmir, Darjeeling, Sikkim).
• Predominant coal deposits (bituminous and anthracite) in this area, constituting 98% of India's coal.

Jurassic Rock System:

• Formed due to marine transgression in the latter part of the Jurassic period.
• Found in Jaisalmer area of Rajasthan, Kutch, Guntur, and Rajamundry, with limestone, shales, and sandstones.

Deccan Trap (Cretaceous Period):

• Spreads over Kachchh (Kutch), Kathiawar, Gujarat, Madhya Pradesh, Maharashtra, and parts of Andhra Pradesh.
• Result of intense volcanic activity, with basaltic lava deposits used for building roads.
• Regur soil (black soil) developed on it, suitable for cotton cultivation.

Tertiary Rock System:

• Formed from Eocene to Pliocene, marked by the birth of the Himalayas and the age of mammals.
• Divided into Eocene, Oligocene, and Miocene systems.
• Eocene System: Mainly found in Jammu and Kashmir, Himachal Pradesh, Rajasthan, Gujarat, and North-Eastern India.
• Oligocene System:Poorly developed in India, found in the Barail series of Assam.
• Miocene System: Fully developed in India, found in tertiary areas of the extra peninsula.
• Quaternary Rock System: Divided into two subdivisions without a clear-cut boundary between them.
• The Pleistocene era, characterized by a cold climate and glaciations, witnessed the origin of the Himalayas. In contrast, the more recent division, beginning around 1200 years ago after the withdrawal of the last glaciations, is associated with the formation of the Northern plains and coastal regions.
• The formation of the Himalayan mountain resulted from the folding process driven by compressional forces arising from the collision between the Indian and Eurasian plates during the tertiary era of the Cenozoic period. This process, occurring between the middle of the Pliocene and Eocene periods, led to the contraction of the Tethys sea and the subsequent formation of the Indus Tsangpo Suture Zone (ITSZ).
• Key milestones in the Himalayan geological timeline include the Oligocene epoch, when the great Himalayas originated, and the development of the Main Central Thrust (MCT) structure towards the end of the Oligocene epoch. 
• The lesser/middle Himalayas took shape in the Miocene period, accompanied by the formation of the Main Boundary Fault (MBF) at its conclusion. Subsequently, the Shivalik Himalayas emerged during the Pliocene epoch, coinciding with the development of the Himalayan Frontal Fault (HFF) structure at the end of the Pliocene.
• This intricate structural arrangement represents the subduction of the Indian plate beneath the Eurasian plate. Post the Pleistocene ice age, the Northern plains of India originated as a result of the deposition of sediments carried by rivers descending from the Himalayas.
• Notable quaternary formations include ice age deposits in Kashmir, the formation of Alluvial plains in North India, the creation of Rajasthan deserts, the Rann of Kutch, laterite formation in the peninsula, and the development of regur soils. Kashmir and the Himalayas witnessed the deposition of ice age deposits, contributing to the diverse geological history of the region.

Prelims Facts

• The deposits of the Ancient Tethys Sea were folded to form the

-Himalayas [JPSC (Pre) 2011]

•  Which part of India has the oldest rocks in the country?

- Peninsular India [JPSC (Pre) 2013]

• Basaltic lava rocks over Indian Deccan Plateau are formed in

- Cretaceous Period (UKPSC (Pre) 2014]

•  The river Damodar, Koel and Subarnarekha originate from Chota Nagpur Plateau

[BPSC (Pre) 2022]

• The Indian Sub-continent was originally part of a huge mass called

Gondwana Continent (IAS (Pre) 1995]

•  In which part of Uttarakhand are artesian wells found

- Tarai (UKPSC (Mains) 2006)

• Sindhu Area or the Indus Valley Region is a

-Desert Region (MPPCS (Pre) 2018]

•  Rajasthan desert or Thar desert is the expanse of Pleistocene or recent

deposits [UPPCS (Pre) 2018]

•  Kuttanad or Kuttanadu of Kerala is famous for -The region with lowest altitude in India

Which is the oldest Rock System of India?

• The most mineralized Rock System of India is

- Dharwar System (CGPCS (Pre) 2011]

• Which rock system is also known as store storehouse of minerals?

- Dharwar System [UPPSC (Pre) 2017

• Which Rock System provides over 90% of the coal in India?

- Gondwana System (UPPSC (Pre) 2017]

• The correct sequence of geomorphic structure present in india, from oldest to youngest?

- Dharwar-Cuddapah-Vidhyan-Gondwana [BPSC (Pre) 1998]

 Which rock system in India is more recent in origin? Quaternary Rock System [CGPSC (Pre) 2012]

• The North-West part of the Indian peninsula was converted into a great center of Vulcanicity in

- The whole of the cretaceous period [IAS (Pre) 2019]

•  Which is the most common Rock of the Archaean Rock System? Gneiss [HPSC (Pre) 2023

- Archaen System (HPSC 2023, CGPCS (Pre) 2013)

• Dharwar System belongs to Which Rock System?

- Archaean Rock System [HPSC (Pre) 2023

Self Check 

1. Which of the following was not a part of Gondwanaland?

(a) Europe

(b) Africa

(c) India

(d) Australia

2. What is the smallest division of 'geological time scale'?

(a) Era

(b) Eon

(c) Epoch 

(d) Period

3. Which of the following rocks are called as

'Precambrian rocks'?

(a) Tertiary

(b) Archaean

(c) Cretaceous

(d) None of these

4. Which of the following is the oldest mountain range in India?

(a) Aravalli

(b) Himalayas

(c) Nilgiri

(d) Satpura

5. Which of the following rock system in India, is also known as 'storehouse of minerals'?

(a) Archaean rock system 

(b) Dharwar system

(c) Cudappah system

(d) Vindhyan system

6. The Cudappah rock system found in which State?

(a) Jharkhand

(b) Rajasthan

(c) Madhya Pradesh

(d) Andhra Pradesh

7. The Vindhyan mountains form a dividing line between the Ganges Plain and..... plateau.

(a) Malwa

(b) Deccan

(c) Chota Nagpur

(d) Baghelkhand

8. The Dravidian rock system is found in which region?

(a) Spiti valley

(b) Damodar valley

(c) Narmada valley

(d) Chota Nagpur plateau

9. Damodar and Mahanadi Valley in the Eastern

India is the depository of the ..

(a) Dharwar system

(b) Cuddapah system

(c) Vindhyan system

(d) Gondwana system

10. The Deccan trap was formed by which of the following activity?

(a) Mesozoic vulcanicity

(b) Cenozoic vulcanicity

(c) Palaeozoic vulcanicity

(d) Cretaceous vulcanicity

11. The Deccan trap was formed by which of the following activities?

(a) Dharwar vulcanicity

(b) Palacozoic vulcanicity

(c) Mesozoic vulcanicity

(d) Cretaceous vulcanicity

12. Which of the following is the characteristic feature of Narmada Valley?

(a) Aeolian origin

(b) Glacial origin

(c) Volcanic origin

(d) Structural origin

13. Which of the following rock systems of India is of recent origin?

(a) Cudappah

(b) Dharwar

(c) Vindhyan

(d) Gondwana

14. The Deccan trap formation was caused by

(a) shield eruption

(b) composite eruption

(c) caldera eruption

(d) flood basalt eruption

15. If there were no Himalayan ranges, what would have been the most likely geographical impact on India?

IAS (Pre) 2010

1. Most of the countries would experience the cold waves from Siberia.
2. The Indo-Gangetic plain would be devoid of such extensive alluvial soils.
3. The pattern of the monsoon would be different from what it is at present.

Codes

(a) Only 1

(b) 1 and 3

(c) 2 and 3

(d) All of these

Know Right Answer

1 (a)

2 (c)

3 (b)

4 (a)

5 (b)

6 (d)

7 (b)

8 (a)

9 (d)

10 (d)

11 (d)

12 (d)

13 (d)

14 (d)

15 (d)