Model Answer
0 min readIntroduction
The Himalayas, a young and dynamic mountain range, are a result of the ongoing collision between the Indian and Eurasian tectonic plates. This collision has not been uniform, leading to distinct longitudinal tectonic subdivisions. Understanding these subdivisions is crucial for comprehending the region’s geomorphology, seismicity, and resource distribution. These subdivisions, broadly categorized based on their relief, geological structure, and tectonic setting, provide insights into the complex processes shaping the Himalayan landscape. The Himalayas extend for approximately 2,500 km, exhibiting significant variations along its length.
Tectonic Subdivisions of the Himalayas
The Himalayas are conventionally divided into four parallel longitudinal zones, from north to south:
1. The Greater Himalayan Zone (High Himalayas)
- Formation: Formed by the compression and uplift of the pre-Himalayan sedimentary rocks and the underlying crystalline basement.
- Characteristics: Highest peaks (above 6000m), rugged terrain, permanent snow cover, glaciers. Composed of metamorphic rocks (gneiss, schist) and granites.
- Tectonic Feature: Marked by the Main Central Thrust (MCT), a major detachment surface.
2. The Lesser Himalayan Zone (Middle Himalayas)
- Formation: Formed by the uplift of the Tethys sediments over the Indian plate.
- Characteristics: Altitudes ranging from 3700-4500m, characterized by steep slopes, deep valleys, and forested regions. Predominantly composed of Proterozoic and Paleozoic sedimentary rocks.
- Tectonic Feature: Bounded by the Main Boundary Thrust (MBT) to the south and the MCT to the north.
3. The Sub-Himalayan Zone (Outer Himalayas/Siwalik Range)
- Formation: Formed by the accumulation of sediments eroded from the higher Himalayas in the foredeep basin.
- Characteristics: Lowest altitudes (600-1200m), relatively gentle slopes, and composed of unconsolidated sediments (sandstone, shale, conglomerate).
- Tectonic Feature: Bounded by the Himalayan Frontal Thrust (HFT) to the south.
4. The Syntaxial Zone
- Formation: Represents the zone of abrupt bending of the Himalayas around the eastern and western syntaxes (Northeast and Northwest).
- Characteristics: Highly deformed and complex geological structure. Marked by tight folds and faults.
- Tectonic Feature: The syntaxial bends are associated with lateral faulting and strike-slip movements.
Regional Variations: The subdivisions are not uniform throughout the Himalayas. In the western Himalayas, the Zanskar and Ladakh ranges represent extensions of the Greater Himalayan Zone, while in the eastern Himalayas, the Patkai and Naga hills represent a different tectonic setting.
| Zone | Altitude (approx.) | Rock Type | Thrust Boundary |
|---|---|---|---|
| Greater Himalayan | >6000m | Metamorphic, Granite | MCT |
| Lesser Himalayan | 3700-4500m | Sedimentary (Proterozoic & Paleozoic) | MBT |
| Sub-Himalayan | 600-1200m | Unconsolidated Sediments | HFT |
| Syntaxial | Variable | Highly Deformed | N/A |
Conclusion
The tectonic subdivisions of the Himalayas reflect the complex interplay of tectonic forces and geological processes. These zones are not static but are continuously evolving due to the ongoing collision of the Indian and Eurasian plates. Understanding these subdivisions is vital for hazard assessment (earthquakes, landslides), resource management, and sustainable development in the Himalayan region. Further research and monitoring are crucial to unravel the intricacies of this dynamic mountain belt.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.