Intraplate deformation

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Figure 1: East Asia topographic map. The large brown area is the Tibetan plateau and the Tien Shan mountains to the northwest. Almost the whole central landmass in view is deformed from the collision of India into Asia around 50 million years ago. East Asia topographic map.png
Figure 1: East Asia topographic map. The large brown area is the Tibetan plateau and the Tien Shan mountains to the northwest. Almost the whole central landmass in view is deformed from the collision of India into Asia around 50 million years ago.

Intraplate deformation is the folding, breaking, or flow of the Earth's crust within plates instead of at their margins. This process usually occurs in areas with especially weak crust and upper mantle, such as the Tibetan Plateau (Figure 1). Intraplate deformation brings another aspect to plate tectonic theory.

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Crustal deformation processes

The theory of plate tectonics states that the Earth's lithosphere (crust and upper mantle) is made up of rigid plates that "float" on top of the asthenosphere (lower mantle) and move relative to one another. As the plates move, the crust deforms dominantly along the plate margins. Intraplate deformation differs from that respect by the observation that deformation can occur anywhere the crust is weak and not just at plate margins.

Deformation is the folding, breaking, or flow of rocks. There are many different types of crustal deformation depending on whether the rocks are brittle or ductile. The aspects that determine these properties are due to certain temperatures and pressures that rocks experience within the Earth. Therefore, temperature and pressure control deformation processes. Ductile rocks tend to bend, fold, stretch, or flow due to compressional or extensional forces. Brittle rocks, on the other hand, tend to break. The zone where the crust breaks is termed a fault. There are three main types of faults: [1] normal faults, reverse faults and strike slip (transform) faults. All of these are ways the crust can deform is due to the different types of plate margins, which are: [2] divergent boundaries, convergent boundaries, and transform boundaries.

These three boundaries do not always form perfectly and this can lead to a mixed boundary. Mixed boundaries can be a combination of a transform with convergence or a transform with divergence.

Intraplate deformation examples

Asia

Figure 2: Same image as Figure 1 but without any intraplate deformation throughout Asia from the India-Asia collision. India-Asia collision with no intraplate deformation.jpg
Figure 2: Same image as Figure 1 but without any intraplate deformation throughout Asia from the India-Asia collision.

Central/East Asia is possibly the best example of large-scale intraplate deformation. The formation and uplift of the Tibetan plateau and the Himalayan mountain range started in the Cenozoic era around 50 million years ago when the Indian plate collided with the Eurasian plate. [3] The collision caused much shortening of the lithosphere, adding to increased crustal thickness and high stress in the Himalaya/Tibet region. [3]

Many geophysical observations in Tibet show a weak crustal zone and suggest that the middle to lower crust may contain fluids and be partially melted. [4] As the Himalayan-Tibet region began to rise, lateral extrusion of the crust in the Tibetan plateau gradually became the dominant mechanism for accommodating the collision and crustal shortening. [4] The lateral extrusion is sliding dominantly to the east and out of India's path. Eastern Tibet is traditionally interpreted as being part of a broad accommodation zone. [5] Much of the eastern movement is due to major strike-slip faults. [6] These strike-slip faults, along with the other faults in Tibet could still be interpreted as on a plate margin though. True intraplate deformation occurs farther north in areas such as Mongolia or the Tian Shan mountains. These areas display true intraplate deformation because there is still much faulting and folding to accommodate some of the crustal shortening from the India/Eurasia collision hundreds of kilometers away from the plate margin.

See also

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<span class="mw-page-title-main">Altyn Tagh fault</span>

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<span class="mw-page-title-main">Bangong suture</span>

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<span class="mw-page-title-main">Tectonics of the Tian Shan</span>

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<span class="mw-page-title-main">Karakoram fault system</span> Fault system in the Himalayan region across India and Asia

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<span class="mw-page-title-main">Paul Tapponnier</span> French geologist (1947–2023)

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<span class="mw-page-title-main">Paleogeography of the India–Asia collision system</span>

The paleogeography of the India–Asia collision system is the reconstructed geological and geomorphological evolution within the collision zone of the Himalayan orogenic belt. The continental collision between the Indian and Eurasian plate is one of the world's most renowned and most studied convergent systems. However, many mechanisms remain controversial. Some of the highly debated issues include the onset timing of continental collision, the time at which the Tibetan plateau reached its present elevation and how tectonic processes interacted with other geological mechanisms. These mechanisms are crucial for the understanding of Mesozoic and Cenozoic tectonic evolution, paleoclimate and paleontology, such as the interaction between the Himalayas orogenic growth and the Asian monsoon system, as well as the dispersal and speciation of fauna. Various hypotheses have been put forward to explain how the paleogeography of the collision system could have developed. Important ideas include the synchronous collision hypothesis, the Lhasa-plano hypothesis and the southward draining of major river systems.

Magmatism along strike-slip faults is the process of rock melting, magma ascent and emplacement, associated with the tectonics and geometry of various strike-slip settings, most commonly occurring along transform boundaries at mid-ocean ridge spreading centres and at strike-slip systems parallel to oblique subduction zones. Strike-slip faults have a direct effect on magmatism. They can either induce magmatism, act as a conduit to magmatism and magmatic flow, or block magmatic flow. In contrast, magmatism can also directly impact on strike-slip faults by determining fault formation, propagation and slip. Both magma and strike-slip faults coexist and affect one another.

References

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