Peninsular Plateau

The Peninsular Plateau of India is the oldest, most structurally stable, and largest physiographic division of the country, covering an area of approximately 16 lakh square kilometers. It forms an irregular inverted triangle with its base running parallel to the Northern Plains and its apex pointing toward Kanniyakumari.

Tectonic Origin and Composition

The Peninsular Plateau represents a detached fragment of the ancient Gondwanaland shield. It is composed of highly metamorphosed Archean gneisses, granites, and schists, alongside extensive volcanic basaltic sheets. Structurally, the plateau has remained a stable landmass since its formation, experiencing vertical epeirogenic movements (crustal uplift and subsidence) rather than the intense horizontal folding that characterized the Himalayas. The general slope of the plateau is from west to east, as evidenced by the direction of major river systems like the Godavari, Krishna, and Kaveri, with the exception of the Narmada and Tapi rivers, which flow westward through structurally controlled rift valleys.

Key Structural Lineaments and Faults

• Narmada-Tapi Rift Valley: A prominent structural depression formed by the down-faulting of crustal blocks (grabens) between the Vindhyan and Satpura horst ranges.
• Malda Fault (Garo-Rajmahal Gap): A tectonic depression that separated the main Peninsular block from its northeastern extension (Meghalaya Plateau) during the Himalayan orogeny, later filled with alluvium by the Ganga and Brahmaputra rivers.
• Great Boundary Fault (GBF): A structural fault line that separates the ancient folded Aravalli Range from the Vindhyan sedimentary formations.

Major Structural Subdivisions

The Peninsular Plateau is divided into three macro-regions based on relief, geological structures, and distinct geomorphic features.

1. The Central Highlands

The Central Highlands occupy the northern part of the Peninsular Plateau, bounded by the Aravalli Range to the northwest, the Vindhyan Range to the south, and the Northern Plains to the north.

• The Aravalli Range: One of the oldest relict fold mountain systems in the world, stretching from Gujarat through Rajasthan to Delhi. It is highly dissected and denuded. Its highest peak is Guru Shikhar (1,722 meters) located on Mount Abu.
• The Malwa Plateau: An undulating volcanic plateau composed of Deccan basalt sheets. It drains into the Yamuna River via the Chambal, Sindh, Betwa, and Ken rivers, creating a highly dissected “Chambal badland” or ravine topography due to intense gully erosion.
• Bundelkhand and Baghelkhand: The eastward extensions of the Malwa Plateau characterized by old Archean granite gneisses (Bundelkhand) and sandstones/limestones (Baghelkhand).
• The Chotanagpur Plateau: Represents the easternmost boundary of the Central Highlands, covering Jharkhand, parts of Odisha, and West Bengal. Lined with Gondwana coal fields along the Damodar valley, it is known as the “Mineral Heart of India.” It features “Pat lands,” which are high-altitude, flat-topped laterite plateaus.

2. The Deccan Plateau

The Deccan Plateau is a massive basaltic tableland lying south of the Narmada River, covering an area of nearly 5 lakh square kilometers.

• The Deccan Trap: A thick sequence of volcanic basaltic lava flows formed during the late Cretaceous period through fissure eruptions. The weathering of this basaltic rock has produced highly fertile black soil (regur), which is ideal for cotton cultivation.
• The Maharashtra Plateau: Forms the northern part of the Deccan Trap, almost entirely underlain by basaltic rocks.
• The Karnataka Plateau (Mysore Plateau): Composed of ancient Archean rocks. It is divided into the mountainous forest region called “Malnad” and the rolling plain area called “Maidan.” It houses the Baba Budan Hills, famous for early coffee cultivation and iron ore deposits.
• The Telangana Plateau: Composed of Archean gneisses, featuring a rolling landscape with numerous “tors” (isolated, weathered granitic rock piles) and tank irrigation systems due to its impermeable rock structure.

3. The Northeastern Extension (Meghalaya Plateau)

The Meghalaya Plateau (comprising the Shillong Plateau and Karbi Anglong Hills) is an outlier of the Peninsular Plateau.

• Geological Continuity: It is structurally part of the Peninsular shield but stands isolated due to the Malda Fault subsidence.
• Major Hill Ranges: From west to east, it comprises the Garo, Khasi, and Jaintia hills. These hills are named after the indigenous tribes inhabiting them.
• Climatic Extremes: The funnel-shaped orientation of these southern hills traps southwest monsoon winds, leading to extreme orographic rainfall at Cherrapunji and Mawsynram (the wettest place on Earth).

Flanking Mountain Walls: Ghats Comparison

The Peninsular Plateau is buttressed by continuous to semi-continuous mountain walls along the coastlines, meeting at the Nilgiri Hills knot.

Key Mountain Ranges, Peaks, and Passes

Prominent Peninsular Peaks

• Anamudi (2,695 m): Located in Kerala; highest peak of the Western Ghats and the entire Peninsular India.
• Doddabetta (2,637 m): Located in Tamil Nadu; highest peak in the Nilgiri Hills.
• Guru Shikhar (1,722 m): Located in Rajasthan; highest peak of the Aravalli Range.
• Dhupgarh (1,350 m): Located near Pachmarhi; highest peak of the Satpura Range.
• Sadbhawna Shikhar / Kalumar Peak (752 m): Highest peak of the Vindhyan Range.

Crucial Mountain Passes

• Thal Ghat: Connects Mumbai to Nashik; cuts through the northern Sahyadris.
• Bhor Ghat: Connects Mumbai to Pune; facilitates key rail and road networks.
• Pal Ghat (Palakkad Gap): A major structural break separating the Nilgiri Hills from the Anaimalai Hills; connects Coimbatore in Tamil Nadu with Palakkad in Kerala.
• Senkottai Gap: Connects Kollam (Kerala) with Madurai (Tamil Nadu) through the Cardamom Hills.

Mineral Resources and Tectonic Trivia

Dharwar System Economic Significance

The ancient Dharwar sedimentary-metamorphic rock system found extensively in Karnataka, Madhya Pradesh, and Jharkhand is the most mineralized rock system in India. It contains major reserves of iron ore (Kudremukh, Baba Budan Hills), manganese, copper, lead, zinc, and gold (Kolar Gold Fields).

Gondwana Formations

The structural troughs of the Damodar, Mahanadi, and Godavari river valleys preserve thick layers of Gondwana sedimentary formations. These systems hold more than 98% of India’s metallurgical and thermal coal reserves.

The Nilgiri Biosphere Knot

The Western Ghats and Eastern Ghats converge at the Nilgiri Hills. This region forms a critical ecological tri-junction between Karnataka, Kerala, and Tamil Nadu, acting as a major biodiversity hotspot that preserves endemic species like the Nilgiri Tahr and Lion-tailed Macaque.