Evolution of the Himalayas | Geology Optional Notes for UPSC PDF Download

Geology of the Himalayas

• The Himalayan mountain range extends from the Brahmaputra to the Indus River, spanning over 2500km with a width ranging between 200-250km.
• Understanding the geology of the Himalayas is crucial for comprehending the formation of large mountain ranges and how these regions evolve over time.
• These mountains significantly impact the daily lives of the inhabitants living in their vicinity.

Importance of Education

• Education plays a pivotal role in disseminating knowledge about the Himalayas and their geological significance.
• A literature review has been compiled to facilitate the delivery of an effective Students' Programme focusing on Landslides and Environment by Geology for Global Development.
• This material is tailored for a Schools conference aimed at children aged 14-16 in Leh, the Ladakh Region of India, as well as the nomadic Changpa Tribe.

Topics Covered in the Summary

• The summary encompasses the formation of the Himalayas, their glaciation, quaternary geology, current tectonics, and natural resources.
• Special attention is given to information directly relevant to the Ladakh region, including major faults and the occurrence of landslides, which pose significant risks to the local population.

Formation of the Himalayas

• Approximately 130 million years ago, India initiated its northward drift as a result of tectonic plate movements, leading to the closure of the Tethys Ocean.
• Fossil evidence indicates that this northward movement persisted until about 65 million years ago when India eventually collided with the Asian landmass.
• The collision between India and Asia triggered subduction along the Indus Suture, which likely contributed to the formation of the Himalayan Batholiths.
• This subduction process created a collision zone, causing the material to buckle downwards.
• Subduction activities also gave rise to the Eocene Transgression and led to decreased spreading rates in the Indian Ocean.
• Isostatic adjustments in the mountain belt began around 20 million years ago due to the collision.
• Following a period of stalling, the movement resumed, but the Indus Suture had become too thick and granitized, prompting the movement to shift along a new line of weakness.
• The formation of Gneisses and Schists reduced resistance, allowing the Indian subcontinent to be under-thrusted, forming a double layer of continental crust.
• Further isostatic adjustments, approximately 5 kilometers deep, were necessary to accommodate the new geological structure.
• As a result of these processes, the Himalayas did not achieve their current height above sea level until the Late Pliocene - Early Pleistocene period.
• Notably, the absence of Blueschist Facies rocks suggests that these geological events unfolded gradually.

Main Thrust Faults in the Himalayas

• The Himalayas feature three primary thrust faults that emerged during the isostatic adjustment phase: Main Central Thrust (MCT), Main Boundary Thrust (MBT), and Main Frontal Thrust (MFT).
• The MCT, spanning kilometers in scale, serves as a mylonitic zone separating the High Himalayan Crystalline from the lower Tertiary sediments in the Lesser Himalayas.

Geological Layers in the Himalayan Region

• The geological composition of the Himalayan region reveals a diverse array of rock formations and sedimentary layers.
• The base of the High Himalayas remains a mystery, with Cambrian rocks identified as the oldest strata.
• There is a potential absence of upper Devonian rocks, and an unconformity is noted between the Carboniferous and Permian rock layers.
• The sequence culminates in Eocene marine sediments, with the Tibetan Slab positioned above this sedimentary sequence.
• The Tibetan Slab comprises highly metamorphosed Palaeozoic and Mesozoic sediments, with its lower boundary linked to the MCT.
• The sediments within the Tibetan Slab resemble those typically found in a platform environment, such as a continental shelf.

Division of Himalayan Nappes

• The Main Boundary Thrust (MBT) demarcates the Nappes of the Lesser Himalayas from the Sub-Himalayas, consisting mainly of Tertiary sediments.
• The Lesser Himalayas' sediments were formed in various aquatic environments, including shallow water, tidal areas, lagoons, and continental settings.
• In contrast, the Sub-Himalayas predominantly exhibit terrestrial sedimentation.
• Granitic formations are prevalent in the Higher Himalayas, adjacent to the MCT, as well as in the Lower Himalayas, close to the MBT.

Glaciation and Quaternary Geology

• Himalayan Glacial Cycles

  The Himalayas underwent three glacial cycles during the Pliocene and the Pleistocene. These cycles influenced climate patterns and led to the development of monsoons. As a result, the region experienced increased aridity.

• Impact on Global Climate

  The uplift of the Himalayas had a significant impact on global climate. The region's aridity produced dust and strong winter winds, potentially contributing to global cooling.

• Early Quaternary Glaciation

  Evidence suggests extensive regional glaciation during the early Quaternary period, with the formation of U-shaped valleys, moraines, and till. The maximum glacial advance occurred around 63,000 years ago.

• Recent Glacial Changes

  Climate change has accelerated the melting of Himalayan glaciers. This has implications for water resources in the region, as glaciers provide water for local populations. Changes in wind circulation and temperature variations are affecting glaciers differently across the Himalayas.

Current Tectonics

• The current convergence between India and Asia is about 58mm per year, primarily through seismic activities.
• Around one-third of the current convergence-rate between India and Asia is accountable for the shortening, uplift, and moderate seismic activity in the Himalayas.
• Ruptures along thrust faults are due to crustal shortening, leading to earthquakes.
• Shortening and topography are closely linked in the Himalayas, notably in the Longman Shan Range on the eastern side.

Earthquakes in the Himalayan Region

• Between 1991 and 2001, India encountered five significant earthquakes.
• The Himalayan zone likely still has stored strain that could trigger a major earthquake with slips exceeding 6m in certain areas.
• An illustration of a substantial rupture in the Himalayas is the Wenchuan Earthquake of 2008 in the Longman Shan Range, measuring 7.9 in magnitude.
• The Wenchuan Earthquake resulted in substantial casualties and aftershocks, affecting nearby populations.

Contraction in the Himalayas

• Contraction in the Himalayas is happening at an average rate of approximately 17mm per year, predominantly along the Main Frontal Thrust (MFT).

Figure 1: Longman Shan Range

Image Description: The image depicts the Longman Shan Range with fault lines, epicenter of the Wenchuan Earthquake, aftershocks, and other relevant geographical features.

Summary: Resources in the Himalayas

Exploration History

• In the Himalayas, there are two sedimentary regions near the Central Crystallines that contain hydrocarbon source and reservoir rocks.
• Although oil seeps have been observed in other areas, none have been found within the Himalayan regions of India or Nepal.
• Exploration efforts in the 20th century yielded minimal results, likely due to a lack of understanding of the region's complex structural geology at that time.
• Recent renewed interest may lead to more successful discoveries in the future (Mukhopadhyay 2008).

Mineral Resources

• Peer-reviewed literature on mineral resources specific to the Himalayas is scarce.
• Information on minerals in the Himalayas is derived from general knowledge of mineral deposits in collisional settings and specific data from non-peer-reviewed sources.
• While indications suggest the Himalayas are not highly mineralized, there is a possibility of economically significant metal deposits within the region (Wilson & Wilson, 2014).
• The lack of substantial mineralization could be attributed to the relatively young age of the Himalayas, hindering the development of hydrothermal systems that facilitate metal precipitation into the crust (Mitchell & Garson 1983).
• Ophiolites in the Himalayas contain chromite and copper sulphide, offering potential resources due to the abundance of these obducted slabs (Wilson & Wilson, 2014).

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