Deccan Volcanic Province | Geology Optional Notes for UPSC PDF Download

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Deccan Traps: A Geological Marvel

• During the end of the Cretaceous period, there was a significant volcanic activity phase in peninsular India.
• This event marked a notable occurrence in Indian geology, characterized by the outpouring of numerous lava flows primarily through fissure-type volcanic eruptions.
• The lava spread over a vast area of the Deccan Plateau in western and central India, forming what is known globally as one of the Large Igneous Provinces, specifically the Deccan Traps or Deccan Volcanic Province.
• The term "Deccan Traps" was coined by W. H. Sykes in 1833, with "Deccan" originating from the Sanskrit word "Dakshin," signifying south or southern, and "Traps" from the Scandinavian word "Traps/Trappa," indicating a step-like appearance.
• Hence, the name "Deccan Traps" denotes the step-like structure of the basaltic landscape on the Deccan Plateau.
• The lava flows of the Deccan Traps shaped a plateau-like topography with terraces resembling steps.
• These lava flows are primarily composed of basalt, giving rise to the distinctive appearance of the region.

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Deccan Traps

• The Deccan Traps, a geological formation in India, are massive volcanic rock layers known as Flood Basalts due to their extensive coverage.
• These lava flows emerged on the surface in regions of peninsular India composed of rocks dating back to the Precambrian to Mesozoic eras.
• The Deccan Traps consist of various lava flows, each with different thicknesses ranging from a few meters to up to 40 meters.
• A total of 48 distinct lava flows have been identified within the Deccan Traps, primarily in the form of expansive horizontal sheets.
• The maximum thickness of the Deccan Traps reaches about 2.5 kilometers in the western region near Mumbai, while it is thinner towards the east.

Distribution

• The Deccan Traps, hosting one of the world's significant igneous provinces, span approximately 500,000 square kilometers, primarily in western and central India.
• This geological formation extends across states like Maharashtra, Madhya Pradesh, Chhattisgarh, Andhra Pradesh, Telangana, Karnataka, Gujarat, Rajasthan, Goa, and Daman and Diu in peninsular India.

Geographical Map

• A map of India illustrates the extensive spread of the Deccan Traps, showcasing its presence in various regions such as Mumbai, Central India, Maharashtra, and beyond.

Deccan Traps Classification

• Lithological Composition

  • The Deccan Traps primarily consist of fine to medium grained, black to dark grey basaltic rocks.
  • Mainly composed of tholeiitic basalts, although other igneous rocks like alkali-olivine basalts, rhyolites, trachytes, and more are also present.
  • Intervening the lava flows are thin sedimentary and volcanic ash beds, with volcanic ash beds being a common feature.

• Sedimentary Beds

  • Between successive lava flows, there are sedimentary beds known as intertrappean beds.
  • The sedimentary beds just below the oldest lava flows are called infratrappean or Lameta beds.
  • Both intertrappean and infratrappean beds contain abundant plant and animal remains.

• Stratigraphic Classification

  • The Deccan Traps are classified into three units based on intertrappean beds and fossil content.
  • These units are Upper Traps (450 m thick), Middle Traps (1200 m thick), and Lower Traps (150 m thick).

• Sub-Provinces of Deccan Traps

  • Western Deccan Volcanic Province is a significant subdivision located south of the Narmada river.
  • It encompasses the western, central, and southeastern parts of the Deccan Traps, predominantly in Maharashtra.
  • The Western Ghats region, extending from Mumbai to Ratnagiri, exhibits the thickest traps.
  • Other areas include Aurangabad, Gulbarga, and Nanded within the central and southeastern parts.

Geological Features of Indian Plateaus

• Western Deccan Plateau:

  The Western Deccan Plateau is also known as the Main Deccan Plateau. It covers a significant area of India.

• Malwa Plateau:

  The Malwa Plateau is situated north of the Narmada river and includes regions around Indore, Bhopal, and Sagar in Madhya Pradesh. The Satpura hills separate it from the Western Deccan Volcanic Province.

• Eastern Deccan Volcanic Province:

  The Eastern Deccan Volcanic Province is an isolated lava pile located in Central India, particularly around Chhindwara, Seoni, and Jabalpur in Madhya Pradesh. It is known as the Mandla lobe.

• Saurashtra Plateau:

  The Saurashtra Plateau is a square-shaped trap found between the Khambhat graben in the east and the Son-Narmada fault in the south of Gujarat.

Deccan Traps Study

The Deccan Traps are extensively studied in the Western/Main Deccan Volcanic Province. Various subgroups and formations exist within this region:

• Group: Western Deccan Volcanic Province
• Subgroups and Formations:
  • Wai
  • Lonavala
  • Kalsubai
  • Mahabaleshwar
  • Gondwana Supergroup and Deccan Trap
  • Purandhargad
  • Diveghat
  • Karla
  • Indrayani
  • Ratangad
  • Eou
  • Salher
• Characteristic Features:
  • Simple and aa phyric flows
  • Simple and aa type flows
  • Aphyric aa type flows
  • Compound pahoehoe flows
  • Simple flows of columnar jointed and aphyric types
  • Compound flows of phyric type
  • Simple pahoehoe flows of phyric type

Age and Duration

The Deccan Traps lava flows date back to around the Cretaceous-Palaeogene boundary, approximately 66 million years ago. This period coincides with a significant mass extinction event, known as the K-Pg mass extinction, marking the disappearance of dinosaurs from the Earth's surface.

• Block 2: Stratigraphy of India
  • The K-Pg mass extinction is suggested to be connected with the extensive eruptions of the Deccan Traps.
  • Over the last two decades, there has been significant global interest in determining the age and duration of the Deccan Traps.
  • The age and duration of the Deccan Traps are primarily established by studying the fossils in the intertrappean and infratrappean beds and by conducting radiometric dating of the trap rocks.
• The eruption of the Deccan Traps occurred in three phases:
  • The first phase began with lava flows around 67.5 million years ago, followed by a 2 million-year quiet period.
  • The second phase, considered the primary eruption event, happened around the K-Pg boundary, with approximately 80% of total lava flows occurring during this phase.
  • The third and last phase commenced after the K-Pg boundary around 64 million years ago, with about 14% of the total Deccan Traps lava flows erupting during this phase.
  • The entire volcanic eruption duration for the Deccan Traps is estimated to be around 4 million years, with the majority forming in less than 1 million years during the second phase linked to the K-Pg mass extinction.
• An age range from Maastrictian to Danian (Upper Cretaceous to Lower Palaeocene) has been suggested for the Deccan Traps based on fossils like foraminifers, ostracods, and plants found in the intertrappean and infratrappean beds.
• The Lameta Formation, situated beneath the Deccan traps, covers an area of over 10,000 km² and is found in isolated outcrops in Madhya Pradesh, Gujarat, and Maharashtra.
• Lithologically, the Lameta Formation comprises red and green clays, green sandstone, limestone, gray marls, yellow laminated clays, marlites, and mottled nodular beds, and is renowned for its dinosaur fauna.
• The dinosaurian fauna in the Lameta Formation includes titanosaurids such as Jainosaurus septentrionalis, Isisaurus colberti, and theropods like Indosuchus raptorius, Indosuchus matleyi, Laevisuchus indicus, Lametasaurus indicus, Rajasaurus narmadensis, Rahiolisaurus gujaratensis.