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131-577: The MBT was formed as a result of the collision of the Indian continent with Asia . It developed to relieve stresses from the compression of the continental collision . When the MBT initially formed around 10-25 million years ago, it was a system of thrust faults which accommodated stresses from the compression of the continental collision which led to Himalayan uplift. The Main Himalayan Thrust

262-650: A "chicken or egg" paradox. As mentioned above, a lot has been done on examining how the uplift of the Himalayas and Tibetan Plateau has triggered the onset of the South Asian monsoon. The approach of most studies is to first establish or make use of pre-existing tectonic models to constrain the timing of uplift and topographic evolution, then evaluate the significance of topography in controlling regional climate by numerical modeling . Various significant tectonic models have been discussed in previous sections. However,

393-439: A consequence, a powerful source generating plate motion is the excess density of the oceanic lithosphere sinking in subduction zones. When the new crust forms at mid-ocean ridges, this oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as it conductively cools and thickens. The greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into

524-450: A few tens of millions of years. Armed with the knowledge of a new heat source, scientists realized that Earth would be much older, and that its core was still sufficiently hot to be liquid. By 1915, after having published a first article in 1912, Alfred Wegener was making serious arguments for the idea of continental drift in the first edition of The Origin of Continents and Oceans . In that book (re-issued in four successive editions up to

655-579: A layer of basalt (sial) underlies the continental rocks. However, based on abnormalities in plumb line deflection by the Andes in Peru, Pierre Bouguer had deduced that less-dense mountains must have a downward projection into the denser layer underneath. The concept that mountains had "roots" was confirmed by George B. Airy a hundred years later, during study of Himalayan gravitation, and seismic studies detected corresponding density variations. Therefore, by

786-583: A microcontinent from the major India craton. However, rock records in the Greater Himalayan crystalline complex , which is located south to the Tibetan Plateau and should have contained remnants of the oceanic Greater Indian Basin if it had existed, do not show supporting evidences. No ophiolite obduction from the oceanic Basin nor typical rock suites from arc-trench subduction system are found. The synchronous collision hypothesis limits

917-400: A misnomer as there is no force "pushing" horizontally, indeed tensional features are dominant along ridges. It is more accurate to refer to this mechanism as "gravitational sliding", since the topography across the whole plate can vary considerably and spreading ridges are only the most prominent feature. Other mechanisms generating this gravitational secondary force include flexural bulging of

1048-454: A model to explain how uplift driven by different factor can result in different drainage patterns, where uplifting is the upward movement of landmass with reference to the Earth's center. In the case of tectonic driven uplift , an active thrust front is present, constantly driving crustal materials upwards. This adds weight to the Earth's surface, causing land subsidence . Since the nearer

1179-558: A secondary phenomenon of this basically vertically oriented mechanism. It finds its roots in the Undation Model of van Bemmelen . This can act on various scales, from the small scale of one island arc up to the larger scale of an entire ocean basin. Alfred Wegener , being a meteorologist , had proposed tidal forces and centrifugal forces as the main driving mechanisms behind continental drift ; however, these forces were considered far too small to cause continental motion as

1310-407: A solid crust and mantle and a liquid core, but there seemed to be no way that portions of the crust could move around. Many distinguished scientists of the time, such as Harold Jeffreys and Charles Schuchert , were outspoken critics of continental drift. Despite much opposition, the view of continental drift gained support and a lively debate started between "drifters" or "mobilists" (proponents of

1441-518: A spot is to the active thrust front, the greater the effect of weight the uplifted crust has on the land surface, asymmetric subsidence is resulted. Groundmass nearer to the uplifted crust subside more, while those which are further subside less. This is reflected by the asymmetrical fan shape of sedimentary strata deposited during subsiding, where columns closer to the point of maximum subsidence are thicker while columns further are thinner. Tectonic driven uplift results in longitudinal rivers dominating

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1572-478: A static Earth without moving continents up until the major breakthroughs of the early sixties. Two- and three-dimensional imaging of Earth's interior ( seismic tomography ) shows a varying lateral density distribution throughout the mantle. Such density variations can be material (from rock chemistry), mineral (from variations in mineral structures), or thermal (through thermal expansion and contraction from heat energy). The manifestation of this varying lateral density

1703-731: A thrust fault. Sources Paleogeography of the India%E2%80%93Asia collision system 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 Plate and Eurasian Plate is one of the world's most renowned and most studied convergent systems . However, many mechanisms remain controversial. Some of

1834-438: Is mantle convection from buoyancy forces. How mantle convection directly and indirectly relates to plate motion is a matter of ongoing study and discussion in geodynamics. Somehow, this energy must be transferred to the lithosphere for tectonic plates to move. There are essentially two main types of mechanisms that are thought to exist related to the dynamics of the mantle that influence plate motion which are primary (through

1965-729: Is actually a broken-off fragment of the above mentioned "Neo-Tethys oceanic basin". The bed of the Tethys sea lay on the Kshiroda Plate and was carried along with it towards Eurasia. The southernmost part of the Eurasian plate was actually the Lhasa block, which itself had drifted north and joined the landmass, simultaneous to the drift of the Indian Plate. This, however, is not included in the hypothesis, as it does not gravely affect

2096-453: Is also useful as climate change may promote speciation or trigger extinction. Plate boundary Plate tectonics (from Latin tectonicus , from Ancient Greek τεκτονικός ( tektonikós )  'pertaining to building') is the scientific theory that Earth 's lithosphere comprises a number of large tectonic plates , which have been slowly moving since 3–4 billion years ago. The model builds on

2227-527: Is based on their modes of formation. Oceanic crust is formed at sea-floor spreading centers. Continental crust is formed through arc volcanism and accretion of terranes through plate tectonic processes. Oceanic crust is denser than continental crust because it has less silicon and more of the heavier elements than continental crust . As a result of this density difference, oceanic crust generally lies below sea level , while continental crust buoyantly projects above sea level. Average oceanic lithosphere

2358-412: Is believed that the uplift of the Himalayas and Tibetan Plateau is the major trigger of South Asian monsoon onset, since only such elevated landmass can change regional airflow configurations. On the other, numerical modelling and thermalchronological data suggest that Eocene uplift of the Himalayas and Tibet is driven by monsoon-intensified denudation , i.e. erosional driven uplift. This gives rise to

2489-461: Is called a plate boundary . Plate boundaries are where geological events occur, such as earthquakes and the creation of topographic features such as mountains , volcanoes , mid-ocean ridges , and oceanic trenches . The vast majority of the world's active volcanoes occur along plate boundaries, with the Pacific plate's Ring of Fire being the most active and widely known. Some volcanoes occur in

2620-533: Is called the geosynclinal theory . Generally, this was placed in the context of a contracting planet Earth due to heat loss in the course of a relatively short geological time. It was observed as early as 1596 that the opposite coasts of the Atlantic Ocean—or, more precisely, the edges of the continental shelves —have similar shapes and seem to have once fitted together. Since that time many theories were proposed to explain this apparent complementarity, but

2751-486: Is commonly related to oceanic subduction. Geochemical analysis of the Lhasa Adakite suggests that it is originated from magmatic activities triggered by slab breakoff. This further reinforces the hypothesis that Lhasa block is uplifted during the initial continental collision phase. Later, magmatic activity ceased as the continent collision occurred. Denser materials in the Indian and Asian continental crust sank to

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2882-494: Is conformable with geological evidences available, details remained debated. Although the actual timing of occurrence of various geological events involving the Tibetan Plateau remains widely debated, there is a common consensus on the evolution of continental block configuration through time among what different studies have put forward. Royden et al. (2008) suggested a tectonic reconstruction model to illustrate how continental blocks of North and South Tibet has evolved throughout

3013-492: Is in motion, presents a problem. The same holds for the African, Eurasian , and Antarctic plates. Gravitational sliding away from mantle doming: According to older theories, one of the driving mechanisms of the plates is the existence of large scale asthenosphere/mantle domes which cause the gravitational sliding of lithosphere plates away from them (see the paragraph on Mantle Mechanisms). This gravitational sliding represents

3144-408: Is invoked as the major driving force, through slab pull along subduction zones. Gravitational sliding away from a spreading ridge is one of the proposed driving forces, it proposes plate motion is driven by the higher elevation of plates at ocean ridges. As oceanic lithosphere is formed at spreading ridges from hot mantle material, it gradually cools and thickens with age (and thus adds distance from

3275-424: Is irregular. The complete consumption of the oceanic crust could occur non-synchronously along the collision front. Different methods can be used to constrain the age of collision onset. Commonly used geological evidences include stratigraphy , sedimentology and paleomagnetic data. Stratigraphy and sedimentology indicates the transfer of materials from one continent to another when two continents, meet, as well as

3406-464: Is likely to be wrong due to reasons discussed above. In this model, the Lhasa tectonic block , equivalent to the southern Tibet, experienced initial uplift due to compressional force created when the Indian and Asian continent collided and the Tethys oceanic slab broke off (45—30 Ma). This is supported by the presence of Adakite in the Lhasa block. Adakite is an intermediate to felsic rock which

3537-478: Is most commonly a result of differential heating of land and sea due to specific heat capacity difference. However, in the case of the South Asia monsoon system, the huge pressure gradient force is induced by the Himalayas and Tibetan Plateau. The Himalaya orogenic belt the highest elevated mountain range on Earth. In summer, air mass across the South Asia is heated up in general. On the contrary, airmass above

3668-463: Is present, (3) both the Himalayas and Tibet are absent. Results shows that both condition (1) and (2) are able to produce similar monsoonal climate patterns, meaning that the Himalayas is climatically insignificant. Webb et al. (2017) proposed a model to explain Himalayan topographic evolution by taking slab dynamics into account. The model suggests temporal differences in topographic evolution in

3799-474: Is reduced quickly and continually, while sedimentation rate is also high. Therefore, transverse rivers developed on the uplifted mountain range are able to extend way beyond the foot of the mountain range. Longitudinal rivers only dominate distal parts of the drainage basin. Brookfield (1998) reconstructed the evolution of major river systems of the Indian-Asian collision zone based on tectonic history of

3930-415: Is still advocated to explain the break-up of supercontinents during specific geological epochs. It has followers amongst the scientists involved in the theory of Earth expansion . Another theory is that the mantle flows neither in cells nor large plumes but rather as a series of channels just below Earth's crust, which then provide basal friction to the lithosphere. This theory, called "surge tectonics",

4061-611: Is the main strand of the MBT and has "caused great shattering, inversion and imbricate thrusting". The Surkhet-Ghorahi thrust fault is a northwest trending fault in Central Nepal . It stretches from Surkhet to Ghorahi in over an extent of 90–120 km (56–75 mi). At the western bank of the Bheri River , the fault slips at a rate of 0.75 mm (0.030 in)/yr. The fault shows vertical fault scarp of 30 m (98 ft). The Kathmandu thrust runs from east of

Main Boundary Thrust - Misplaced Pages Continue

4192-728: Is the root Décollement structure, and results in similar fault system splays such as the Main Himalayan Thrust , Main Central Thrust , and the South Tibetan Detachment . These faults accommodated stresses parallel to the MBT and helped the Himalayan mountains grow. Each of these faults served as the primary reliever of strain in the Himalayan Orogeny until being abandoned in a successive chain of intracontinental thrust faults. Currently,

4323-640: Is thought to have initiated. Further studies on Tertiary carbon isotope composition of paleosols could be carried out to examine the shift in C3 / C4 vegetation ratio. C3 and C4 plants practice different carbon fixation mechanism. C4 fixation is more water-efficient and therefore favours plant adaptation to extreme climatic conditions. Therefore, C4 plants are generally more abundant in cold and arid- temperate regions. Carbon isotopes in paleosols are remains of dead plants and therefore accurately reflects climatic regime shifts. Phylogenetic reconstructions of animal taxa

4454-488: Is to consider the relative rate at which each plate is moving as well as the evidence related to the significance of each process to the overall driving force on the plate. One of the most significant correlations discovered to date is that lithospheric plates attached to downgoing (subducting) plates move much faster than other types of plates. The Pacific plate, for instance, is essentially surrounded by zones of subduction (the so-called Ring of Fire) and moves much faster than

4585-407: Is typically 100 km (62 mi) thick. Its thickness is a function of its age. As time passes, it cools by conducting heat from below, and releasing it raditively into space. The adjacent mantle below is cooled by this process and added to its base. Because it is formed at mid-ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid-ocean ridge where it

4716-435: Is used. It asserts that super plumes rise from the deeper mantle and are the drivers or substitutes of the major convection cells. These ideas find their roots in the early 1930s in the works of Beloussov and van Bemmelen , which were initially opposed to plate tectonics and placed the mechanism in a fixed frame of vertical movements. Van Bemmelen later modified the concept in his "Undation Models" and used "Mantle Blisters" as

4847-572: Is widely accepted that the Indian plate began to approach the Eurasian plate during the Mesozoic times as a result of the break up of Gondwana supercontinent . In the Mesozoic time, there was an oceanic basin in between the Lhasa block and the North Tibet continental block. Subduction of the oceanic slab underneath the North Tibet block started in the Triassic . In Jurassic to Cretaceous,

4978-567: The Appalachian Mountains of North America are very similar in structure and lithology . However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparent mechanism for continental drift. Specifically, they did not see how continental rock could plow through the much denser rock that makes up oceanic crust. Wegener could not explain the force that drove continental drift, and his vindication did not come until after his death in 1930. As it

5109-529: 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 . The onset of continental collision is determined by any point along

5240-865: The Main Frontal Thrust is the main thrust fault in the system. The Main Boundary Thrust consists of multiple segments spanning 2,400 km (1,500 mi) in the Himalayas . The Murree fault is a thrust fault which lies in Kashmir . To its southeast, the Drang thrust continues as an extension of the Murree thrust in Himachal . To the southeast of the Murree and Drang faults, the Krol thrust

5371-620: The Qiangtang metamorphic belt in Central Tibet. By the time when the Indian continent and the Asian continent collided, South Tibet has already reached 3–4 km elevation. The compressional force resulted from the Indian-Asian collision further topped up Lhasa block's elevation and triggered crustal thickening in the North Tibet as the Indian continent proceed northwards. Although the timing of Lhasa block thickening in this model

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5502-518: The Tertiary period so as to better understand how Tibet and the South Asian monsoon co-evolved. Quaternary climatic reconstructions of the Tibetan Plateau area are mostly based on pollen analysis, while Mesozoic climatic reconstructions are done by analyzing benthic foraminifera from paleo-oceanic basins. Little study has focused on the Tertiary period, at which the South Asian monsoon

5633-422: The chemical subdivision of these same layers into the mantle (comprising both the asthenosphere and the mantle portion of the lithosphere) and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates , which ride on

5764-736: The fluid-like solid the asthenosphere . Plate motions range from 10 to 40 millimetres per year (0.4 to 1.6 in/year) at the Mid-Atlantic Ridge (about as fast as fingernails grow), to about 160 millimetres per year (6.3 in/year) for the Nazca plate (about as fast as hair grows). Tectonic lithosphere plates consist of lithospheric mantle overlain by one or two types of crustal material: oceanic crust (in older texts called sima from silicon and magnesium ) and continental crust ( sial from silicon and aluminium ). The distinction between oceanic crust and continental crust

5895-473: The lithosphere and asthenosphere . The division is based on differences in mechanical properties and in the method for the transfer of heat . The lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conduction , whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient. This division should not be confused with

6026-514: The plate boundary where the oceanic lithosphere is completely subducted and two continental plates first come into contact. In the case of the India–Asia collision, it would be defined by the first point of disappearance of the Neo-Tethys oceanic crust, where the India and Asia continent come into contact with each other. Such process is defined by a point since the shape of continental margins

6157-462: The "merged" island arc) and the Asian continent at approximately 33 Ma. This hypothesis is mainly based on the observation of lithostratigraphic patterns within and around the Yarlung-Zangbo suture zone (YZSZ). The YZSZ itself consists of ophiolite and basaltic to andesitic volcanic rocks, which is comparable to typical rock suites in an island arc subduction system. The north of

6288-491: The Cretaceous period (145—66 Ma). Diversified scientific evidences have been put forward to support such hypothesis, such as paleomagnetic reconstruction, sedimentology and igneous petrology, structural geology and geochemistry. For example, Ingalls et al. (2018) uses δ O ( oxygen-isotope ) in meteoric water and Δ47 ( clumped-isotope ) in non-marine carbonates to reconstruct paleotemperature and paleoprecipitation of

6419-546: The Earth's rotation and the Moon as main driving forces for the plates. The vector of a plate's motion is a function of all the forces acting on the plate; however, therein lies the problem regarding the degree to which each process contributes to the overall motion of each tectonic plate. The diversity of geodynamic settings and the properties of each plate result from the impact of the various processes actively driving each individual plate. One method of dealing with this problem

6550-484: The East-central and Western Himalayas. Such differences allowed a series of positive climatic feedbacks to occur sequentially and remain sustainable. Feedback mechanisms include topographically-induced monsoon, monsoon-intensified erosion, and erosional-driven uplift (isostatic rebound). Although the discussion of this model is limited to 20 Ma onwards, such concept can be implemented to future studies focusing on

6681-609: The Himalayas and Tibet experiences adiabatic cooling and sinks rapidly, forming an intense high pressure cell. This cell is therefore capable of facilitating landward airflow towards itself, thus sustaining the onshore summer monsoon. The onset of South Asian monsoon is poorly constrained since limited paleoclimatic data is available. It is generally accepted to have occurred during the Eocene-Oligocene climate transition (33.9 Ma onwards). The onset mechanism has long been debated and remained poorly understood. On one hand, it

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6812-527: The Indian-Asian collision. This model also emphasizes the point that the Lhasa block is first deformed, followed by the North Tibet block. Moreover, the collision between the Lhasa block and the North Tibet block occurred later in the East than in the South. This suggests that detail collision mechanisms could be complicated and require further investigation. A single tectonic model is not likely to be able to explain

6943-464: The India–Asia collision zone synchronize with each other, being in favour of a "one-off" collision. As per geological research conducted in 2015, there possibly existed two subduction zones between the Indian and Eurasian plates. A hypothetical lost oceanic plate called the Kshiroda Plate is supposed to have existed between the two subduction zones. It is now believed that this oceanic plate

7074-439: The Mesozoic ocean is closed. The Lhasa continental block and the North Tibet continental block collided with each other, resulting in intense crustal shortening and thickening of the Lhasa block, i.e. South Tibet. The closing of Mesozoic ocean, the continental collision between Lhasa block and North Tibet block and the early crustal thickening of Lhasa block is indicated by the presence of ultra-high pressure metamorphic rocks in

7205-640: The Surkhet-Ghorahi fault near Kathmandu to west of Thimpu . The Gondwana thrust fault system runs from west of Thimpu passing through Bhutan before terminating in West Kameng . In the east it is termed the Garu thrust, though it is a part of the Gondwana thrust. After acting as a thrust fault initially, the Surkhet-Ghorahi may have reactivated as a normal fault—moving the opposite direction of

7336-472: The Tibetan Plateau. This suggests that the Yarlung-Zangbo suture zone is part of the Asian continental margin instead of a separate intraoceanic island. The Greater India Basin hypothesis suggests that there was a two-stage collision between India and Asia continent. The first stage occurred at approximately 50 Ma, where a microcontinent from the Indian plate collided with the Asian continent. It

7467-687: The Tibetan Plateau. It is suggested that the southern part of Tibet is around 3–4 km high and have an average temperature of 10 °C as early as in Late Cretaceous (92 Ma). This shows that southern Tibet has to be already at its present-day sub-equatorial latitude, such that 10 °C, an extremely warm temperature for highly elevated regions, can be maintained. It is now generally accepted that Tibet grew differentially, with its southern part reaching present day elevation first, followed by its northern part. For example, Fei et al. (2017) uses Ar/ Ar and ( U-Th)/He thermochronology to track

7598-462: The YZSZ is the Lhasa terrane of the Tibetan Plateau, while the south of the YZSZ is the Indian superterrane. The fact that the YZSZ separates two continental terrane suggests that it could have been an intraoceanic island arc in the past, locating in between the Asian continental margin (Lhasa terrane) and the Indian continental margin (Indian superterrane) before collision occurred. Volcanic rocks in

7729-458: The Zedong terrane, which belongs to the YZSZ, has high K 2 O content and are classified as shoshonites. Shoshonites are potassium-rich basaltic andesite which are commonly found in modern intraoceanic arc settings. It therefore favours the prediction of the YZSZ as a paleo-intraoceanic island. However, recent studies suggest that volcanic rocks in the Zedong terrane have been altered such that

7860-541: The actual motions of the Pacific plate and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, but rather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drives them along via viscosity-related traction forces. The driving forces of plate motion continue to be active subjects of on-going research within geophysics and tectonophysics . The development of

7991-459: The age of collision onset at 59 Ma by dating the oldest turbidites formed on the passive margin of the India continent, which indicates the incoming of materials from the active Asian continental margin. Geological evidence of rocks younger than 59 Ma and deposited on top of the turbidite sequence can be considered as indicators to reconstruct tectonic evolution after collision had begun. Various evidence documented along NE-SW and NW-SE sections of

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8122-416: The area instead of transverse rivers. Transverse rivers are rivers cutting at right angle to mountain ridges, while longitudinal rivers flow parallel to them. During active uplift and subsidence, accommodation space is created quickly and continually, while erosion rate remains relatively slow. Therefore, transverse rivers developed on the uplifted mountain range are not able to extend beyond the area nearest to

8253-408: The area. It is suggested that the most significant changes in drainage patterns occurred during Pliocene to Quaternary (5.3 Ma onwards). Detail changes in fluvial processes will not be discussed here. Major focuses are how river systems of the area responded to changing geological processes through time, as well as how regional drainage patterns are capable of reflecting tectonic evolution. Before

8384-478: The assumption of a solid Earth made these various proposals difficult to accept. The discovery of radioactivity and its associated heating properties in 1895 prompted a re-examination of the apparent age of Earth . This had previously been estimated by its cooling rate under the assumption that Earth's surface radiated like a black body . Those calculations had implied that, even if it started at red heat , Earth would have dropped to its present temperature in

8515-399: The asthenosphere. This theory was launched by Arthur Holmes and some forerunners in the 1930s and was immediately recognized as the solution for the acceptance of the theory as originally discussed in the papers of Alfred Wegener in the early years of the 20th century. However, despite its acceptance, it was long debated in the scientific community because the leading theory still envisaged

8646-476: The base of the lithosphere. Slab pull is therefore most widely thought to be the greatest force acting on the plates. In this understanding, plate motion is mostly driven by the weight of cold, dense plates sinking into the mantle at trenches. Recent models indicate that trench suction plays an important role as well. However, the fact that the North American plate is nowhere being subducted, although it

8777-495: The bathymetry of the deep ocean floors and the nature of the oceanic crust such as magnetic properties and, more generally, with the development of marine geology which gave evidence for the association of seafloor spreading along the mid-oceanic ridges and magnetic field reversals , published between 1959 and 1963 by Heezen, Dietz, Hess, Mason, Vine & Matthews, and Morley. Simultaneous advances in early seismic imaging techniques in and around Wadati–Benioff zones along

8908-492: The bottom part of the crust, making the lower crust extremely dense and heavy. It thus broke off and sank into the mantle. The removal of the dense lower crust reduced gravitational pull on the Lhasa block and allowed it to rise (30—26 Ma). Together with the intense compressional force and thrusting it experienced amidst collision, intense crustal thickening occurred, resulting in the major phase of uplift in South Tibet. As

9039-505: The change in depositional environment after the oceanic basin is closed and sea water is completely expelled. Paleomagnetic data indicates collision when the paleolatitudes of both continental margins overlap. The onset of the India–Asia collision has been poorly constrained from Late Cretaceous to Oligo - Miocene due to different interpretations of geological evidences by different researchers. The diachronous collision hypothesis involves mechanisms with two stages of collision, where

9170-685: The collision proceed (26—13 Ma), the Northern Tibet continental block experienced compression, thrusting and shortening as well. This interpretation is supported by the thermochronological data of apatite fission tracks from the North Tibetan Plateau, which indicate phases of rapid exhumation and compression from 20 Ma onwards. The Mesozoic model suggested that southern Tibet experienced intense crustal shortening and thickening as early as in Jurassic to Cretaceous time. It

9301-416: The concept of continental drift , an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s. The processes that result in plates and shape Earth's crust are called tectonics . Tectonic plates also occur in other planets and moons. Earth's lithosphere, the rigid outer shell of

9432-413: The concept was of continents plowing through oceanic crust. Therefore, Wegener later changed his position and asserted that convection currents are the main driving force of plate tectonics in the last edition of his book in 1929. However, in the plate tectonics context (accepted since the seafloor spreading proposals of Heezen, Hess, Dietz, Morley, Vine, and Matthews (see below) during the early 1960s),

9563-496: The continental collision occurred (which is defined as 50 Ma or before in Brookfield's model), longitudinal river system had dominated the Asian continent, where major river systems run parallel to the approaching regional thrust. Amidst the collision (which is referred as 20 Ma in Brookfield's model), the shape of river channels were affected by the approaching Indian continent. Although major river systems still flowed parallel to

9694-415: The deep mantle at subduction zones, providing most of the driving force for plate movement. The weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. For much of the first quarter of the 20th century, the leading theory of the driving force behind tectonic plate motions envisaged large scale convection currents in the upper mantle, which can be transmitted through

9825-573: The deformation patterns in these river basins, a two-phase deformation model in the East Himalayas is verified. This shows that rivers are reliable indicators of crustal strain and useful in reconstructing regional tectonic history. Moreover, the Indus and the Ganges river originally flowed parallel to the regional thrust on the Asian continent, but are now flowing perpendicular to it. They crossed

9956-534: The discussions treated in this section) or proposed as minor modulations within the overall plate tectonics model. In 1973, George W. Moore of the USGS and R. C. Bostrom presented evidence for a general westward drift of Earth's lithosphere with respect to the mantle, based on the steepness of the subduction zones (shallow dipping towards the east, steeply dipping towards the west). They concluded that tidal forces (the tidal lag or "friction") caused by Earth's rotation and

10087-466: The driving force for horizontal movements, invoking gravitational forces away from the regional crustal doming. The theories find resonance in the modern theories which envisage hot spots or mantle plumes which remain fixed and are overridden by oceanic and continental lithosphere plates over time and leave their traces in the geological record (though these phenomena are not invoked as real driving mechanisms, but rather as modulators). The mechanism

10218-473: The final one in 1936), he noted how the east coast of South America and the west coast of Africa looked as if they were once attached. Wegener was not the first to note this ( Abraham Ortelius , Antonio Snider-Pellegrini , Eduard Suess , Roberto Mantovani and Frank Bursley Taylor preceded him just to mention a few), but he was the first to marshal significant fossil and paleo-topographical and climatological evidence to support this simple observation (and

10349-515: The first stage starts during the Paleocene to Eocene . The Paleogene arc-continent collision suggests that the Indian continent experienced a two-stage collision. The first stage involves the collision with an intraoceanic island arc in the Tethys Ocean at approximately 55 million years ( Ma ) ago. The second stage involves the collision between the Indian continent (together with

10480-695: The forces acting upon it by the Moon are a driving force for plate tectonics. As Earth spins eastward beneath the Moon, the Moon's gravity ever so slightly pulls Earth's surface layer back westward, just as proposed by Alfred Wegener (see above). Since 1990 this theory is mainly advocated by Doglioni and co-workers ( Doglioni 1990 ), such as in a more recent 2006 study, where scientists reviewed and advocated these ideas. It has been suggested in Lovett (2006) that this observation may also explain why Venus and Mars have no plate tectonics, as Venus has no moon and Mars' moons are too small to have significant tidal effects on

10611-588: The geographical latitudinal and longitudinal grid of Earth itself. These systematic relations studies in the second half of the nineteenth century and the first half of the twentieth century underline exactly the opposite: that the plates had not moved in time, that the deformation grid was fixed with respect to Earth's equator and axis, and that gravitational driving forces were generally acting vertically and caused only local horizontal movements (the so-called pre-plate tectonic, "fixist theories"). Later studies (discussed below on this page), therefore, invoked many of

10742-462: The growth of the Plateau through time and the results are positive. The figure below shows a generalized evolution model of when did different areas of the Tibetan Plateau reaches its present-day elevation. Although the age is not well-constrained, a clear north-younging trend can be observed. The Miocene model suggested that the Indian-Asian collision is the major cause for Tibet's uplift, which

10873-401: The highest topographic features on Earth. It is very rare to see the Earth's crust achieving such a large extent of thickening. This is why Tibet attracts scientific interest. It was previously believed that Tibet uplifting is solely resulted from the Indian-Asian continental collision. However, more and more studies revealed that Tibet might have reached its present-day elevation as early as in

11004-476: 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

11135-718: The interiors of plates, and these have been variously attributed to internal plate deformation and to mantle plumes. Tectonic plates may include continental crust or oceanic crust, or both. For example, the African plate includes the continent and parts of the floor of the Atlantic and Indian Oceans. Some pieces of oceanic crust, known as ophiolites , failed to be subducted under continental crust at destructive plate boundaries; instead these oceanic crustal fragments were pushed upward and were preserved within continental crust. Three types of plate boundaries exist, characterized by

11266-412: The large scale convection cells) or secondary. The secondary mechanisms view plate motion driven by friction between the convection currents in the asthenosphere and the more rigid overlying lithosphere. This is due to the inflow of mantle material related to the downward pull on plates in subduction zones at ocean trenches. Slab pull may occur in a geodynamic setting where basal tractions continue to act on

11397-421: The lithosphere before it dives underneath an adjacent plate, producing a clear topographical feature that can offset, or at least affect, the influence of topographical ocean ridges. Mantle plumes and hot spots are also postulated to impinge on the underside of tectonic plates. Slab pull : Scientific opinion is that the asthenosphere is insufficiently competent or rigid to directly cause motion by friction along

11528-403: The lower mantle, there is a slight westward component in the motions of all the plates. They demonstrated though that the westward drift, seen only for the past 30 Ma, is attributed to the increased dominance of the steadily growing and accelerating Pacific plate. The debate is still open, and a recent paper by Hofmeister et al. (2022) revived the idea advocating again the interaction between

11659-405: The many geographical, geological, and biological continuities between continents. In 1912, the meteorologist Alfred Wegener described what he called continental drift, an idea that culminated fifty years later in the modern theory of plate tectonics. Wegener expanded his theory in his 1915 book The Origin of Continents and Oceans . Starting from the idea (also expressed by his forerunners) that

11790-429: The matching of the rock formations along these edges. Confirmation of their previous contiguous nature also came from the fossil plants Glossopteris and Gangamopteris , and the therapsid or mammal-like reptile Lystrosaurus , all widely distributed over South America, Africa, Antarctica, India, and Australia. The evidence for such an erstwhile joining of these continents was patent to field geologists working in

11921-427: The measurable amount of total convergence expressed by crustal shortening at the surface. Paleomagnetic data suggests that the Indian continent had experienced a N-S extension with minimum extension rates of 40–67 mm/y during 118 and 68 Ma. Such extensional rate is comparable to typical records of intracontinental rifting. Therefore, the hypothesized oceanic Greater India Basin could have existed and separated

12052-476: The mobile ion ratios (e.g. K and Na) are unreliable. Immobile elements such as Zr/TiO 2 ratios should be used instead for classification. New data suggests that volcanic rocks in the Zedong terrane has a calc-alkaline composition, which is common for volcanic island arc but not necessarily intraoceanic island. Moreover, volcanic rocks in the Zedong terrane share a similar geochemical pattern with Lower Jurassic -aged volcanic rocks from southern Lhasa terrane of

12183-568: The motion picture of the Atlantic region", processes that anticipated seafloor spreading and subduction . One of the first pieces of geophysical evidence that was used to support the movement of lithospheric plates came from paleomagnetism . This is based on the fact that rocks of different ages show a variable magnetic field direction, evidenced by studies since the mid–nineteenth century. The magnetic north and south poles reverse through time, and, especially important in paleotectonic studies,

12314-438: The motion. At a subduction zone the relatively cold, dense oceanic crust sinks down into the mantle, forming the downward convecting limb of a mantle cell , which is the strongest driver of plate motion. The relative importance and interaction of other proposed factors such as active convection, upwelling inside the mantle, and tidal drag of the Moon is still the subject of debate. The outer layers of Earth are divided into

12445-470: The north pole, and each continent, in fact, shows its own "polar wander path". During the late 1950s, it was successfully shown on two occasions that these data could show the validity of continental drift: by Keith Runcorn in a paper in 1956, and by Warren Carey in a symposium held in March 1956. The second piece of evidence in support of continental drift came during the late 1950s and early 60s from data on

12576-407: The oceanic crust is suggested to be in motion with the continents which caused the proposals related to Earth rotation to be reconsidered. In more recent literature, these driving forces are: Forces that are small and generally negligible are: For these mechanisms to be overall valid, systematic relationships should exist all over the globe between the orientation and kinematics of deformation and

12707-437: The oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent plate boundaries , the process of subduction carries the edge of one plate down under the other plate and into the mantle . This process reduces the total surface area (crust) of the Earth. The lost surface is balanced by the formation of new oceanic crust along divergent margins by seafloor spreading, keeping

12838-536: The only quantitative model which has assigned a significant role for climate suggests the opposite, i.e. the exhumation of the southern flank of the Tibetan plateau is a result of monsoon-intensified denudation . The channel flow model explains the South Tibetan uplift in two stages. The first stage took place during Eocene to Oligocene . It is hypothesized that the middle part of the Tibet continental crust

12969-589: The planet including the crust and upper mantle , is fractured into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary (or fault ): convergent , divergent , or transform . The relative movement of the plates typically ranges from zero to 10 cm annually. Faults tend to be geologically active, experiencing earthquakes , volcanic activity , mountain-building , and oceanic trench formation. Tectonic plates are composed of

13100-470: The planet. In a paper by it was suggested that, on the other hand, it can easily be observed that many plates are moving north and eastward, and that the dominantly westward motion of the Pacific Ocean basins derives simply from the eastward bias of the Pacific spreading center (which is not a predicted manifestation of such lunar forces). In the same paper the authors admit, however, that relative to

13231-399: The plate as it dives into the mantle (although perhaps to a greater extent acting on both the under and upper side of the slab). Furthermore, slabs that are broken off and sink into the mantle can cause viscous mantle forces driving plates through slab suction. In the theory of plume tectonics followed by numerous researchers during the 1990s, a modified concept of mantle convection currents

13362-426: The plates of the Atlantic basin, which are attached (perhaps one could say 'welded') to adjacent continents instead of subducting plates. It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) are the driving forces which determine the motion of plates, except for those plates which are not being subducted. This view however has been contradicted by a recent study which found that

13493-408: The present continents once formed a single land mass (later called Pangaea ), Wegener suggested that these separated and drifted apart, likening them to "icebergs" of low density sial floating on a sea of denser sima . Supporting evidence for the idea came from the dove-tailing outlines of South America's east coast and Africa's west coast Antonio Snider-Pellegrini had drawn on his maps, and from

13624-406: The proximal part of the Himalayas mountain range. The South Asian monsoon system primarily affects the continents of South Asia and their surrounding water bodies. In this particular system, summer monsoon blows as onshore northeasterly while winter monsoon blows as offshore westerly . The driving force of monsoon systems is the pressure difference between landmasses and waterbodies. This

13755-433: The regional climatic condition was changed. Rainfall and wind intensified denudation and weakened the upper crust mechanically (but not thermally). The molten middle crust was therefore able to break through the upper crust and flow outward to the surface. The dilemma is that the South Asian monsoon was believed to have originated from topographic rise of the Himalayas and Tibetan Plateau. The channel flow model predicts that

13886-405: The regional drainage configuration is very different from how it originally was. River systems were eastward flowing, with the Indus as an exception, before the continental collision started. At present, most rivers are flowing south to southeast. The Salween , Yom , Mekong and Red river are drastically bent around the northeastern "tip" of the Indian continent. By further examining and studying

14017-459: The relationships recognized during this pre-plate tectonics period to support their theories (see reviews of these various mechanisms related to Earth rotation the work of van Dijk and collaborators). Of the many forces discussed above, tidal force is still highly debated and defended as a possible principal driving force of plate tectonics. The other forces are only used in global geodynamic models not using plate tectonics concepts (therefore beyond

14148-428: The relative position of the magnetic north pole varies through time. Initially, during the first half of the twentieth century, the latter phenomenon was explained by introducing what was called "polar wander" (see apparent polar wander ) (i.e., it was assumed that the north pole location had been shifting through time). An alternative explanation, though, was that the continents had moved (shifted and rotated) relative to

14279-399: The ridge). Cool oceanic lithosphere is significantly denser than the hot mantle material from which it is derived and so with increasing thickness it gradually subsides into the mantle to compensate the greater load. The result is a slight lateral incline with increased distance from the ridge axis. This force is regarded as a secondary force and is often referred to as " ridge push ". This is

14410-436: The rise of Tibetan Plateau requires the presence of South Asian monsoon, which leaves the Himalayas as the only possible candidate responsible for initiating the monsoon system. However, a study done by Boos & Kuang (2010) eliminated such possibility. The study uses computer model to simulate the growth and evolution of the South Asian monsoon under three conditions: (1) both the Himalayas and Tibet are present, (2) Only Tibet

14541-491: The southern hemisphere. The South African Alex du Toit put together a mass of such information in his 1937 publication Our Wandering Continents , and went further than Wegener in recognising the strong links between the Gondwana fragments. Wegener's work was initially not widely accepted, in part due to a lack of detailed evidence but mostly because of the lack of a reasonable physically supported mechanism. Earth might have

14672-553: The tectonic activities. According to this hypothesis, the Kshiroda Plate after being subducted under the Eurasian Plate caused the uplift of the Tibetan Plateau and also the delamination of the Indian Plate beneath the plateau. When and how did the Tibetan Plateau reach its present-day elevation has long been widely debated. Tibet has an average elevation of 5 km, which makes it the highest plateau and one of

14803-481: The theory of plate tectonics was the scientific and cultural change which occurred during a period of 50 years of scientific debate. The event of the acceptance itself was a paradigm shift and can therefore be classified as a scientific revolution, now described as the Plate Tectonics Revolution . Around the start of the twentieth century, various theorists unsuccessfully attempted to explain

14934-502: The theory) and "fixists" (opponents). During the 1920s, 1930s and 1940s, the former reached important milestones proposing that convection currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust. Concepts close to the elements of plate tectonics were proposed by geophysicists and geologists (both fixists and mobilists) like Vening-Meinesz, Holmes, and Umbgrove. In 1941, Otto Ampferer described, in his publication "Thoughts on

15065-459: The thrust and extended onto the Indian continent. This is conformable to the above-mentioned model proposed by Burbank (1992). Since tectonic uplift has significantly slowed down nowadays compared to when the collision has just started, the present day Indian-Asian collision region is dominated by erosional processes. Rivers like the Indus and Ganges, which originated from the Lhasa block, are therefore able to flow as transverse rivers and reach beyond

15196-419: The thrust front, where subsidence is the most intense. Instead, longitudinal rivers dominated most of the area. On the contrary, in the case of erosional driven uplift , active thrust front is absent. Uplifting of the crust is driven by isostatic rebound . The fact that materials are constantly eroded and removed reduces weight adding on the Earth's crust, causing it to "bounce" higher. Since erosion dominates

15327-455: The thrust, they bent around both sides of the Indian continent since the collision exerted compressional force to the drainage basin. Such effect is most obviously reflected by the Indus river and the Ganges river. The westward flowing Indus river wraps around the western boundary of the thrust while the eastward flowing Ganges wraps around the eastern boundary of the thrust. In present days,

15458-476: The total surface area constant in a tectonic "conveyor belt". Tectonic plates are relatively rigid and float across the ductile asthenosphere beneath. Lateral density variations in the mantle result in convection currents, the slow creeping motion of Earth's solid mantle. At a seafloor spreading ridge , plates move away from the ridge, which is a topographic high, and the newly formed crust cools as it moves away, increasing its density and contributing to

15589-535: The total convergence. The Greater India Basin model is therefore put forward to explain such observation, where the total amount of convergent has actually been dispersed into two separate stages of crustal thickening, i.e. the uplift of the microcontinent (Tibetan Plateau) and the Himalaya orogeny. The subduction and disappearance of the Great Indian Basin oceanic crust beneath the microcontinent reduces

15720-429: The trenches bounding many continental margins, together with many other geophysical (e.g., gravimetric) and geological observations, showed how the oceanic crust could disappear into the mantle, providing the mechanism to balance the extension of the ocean basins with shortening along its margins. All this evidence, both from the ocean floor and from the continental margins, made it clear around 1965 that continental drift

15851-467: The way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are: Tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere . Dissipation of heat from the mantle is the original source of the energy required to drive plate tectonics through convection or large scale upwelling and doming. As

15982-420: The whole area, uplifting is not limited to sections near to the mountain range. The uplifting rate of the whole drainage basin is rather equal, as reflected by symmetrical shape and equal thickness of sedimentary stratum deposited during uplifting. Erosion driven uplift results in transverse rivers dominating the area instead of longitudinal rivers. During active erosion and isostatic rebound, accommodation space

16113-403: The whole process. For example, although the above-mentioned Mesozoic uplift model is consistent with the onset timing of South Tibet crustal shortening, other details need to be refined. Rivers are features formed by water eroding into the land surface. Drainage patterns provide clues not only to hydrological conditions, but also to geology and tectonic evolution. Burbank (1992) proposed

16244-531: Was feasible. The theory of plate tectonics was defined in a series of papers between 1965 and 1967. The theory revolutionized the Earth sciences, explaining a diverse range of geological phenomena and their implications in other studies such as paleogeography and paleobiology . In the late 19th and early 20th centuries, geologists assumed that Earth's major features were fixed, and that most geologic features such as basin development and mountain ranges could be explained by vertical crustal movement, described in what

16375-508: Was followed by the subduction of the oceanic Great India Basin, which was located in between the microcontinent and the major Indian craton , under the Asian continent. The second stage of collision occurred after the oceanic crust of the Great India Basin had been consumed, where the major Indian craton finally came into contact and collided with the Asian continental margin (including the previously "merged" microcontinent, which

16506-599: Was formed. For a typical distance that oceanic lithosphere must travel before being subducted, the thickness varies from about 6 km (4 mi) thick at mid-ocean ridges to greater than 100 km (62 mi) at subduction zones. For shorter or longer distances, the subduction zone, and therefore also the mean, thickness becomes smaller or larger, respectively. Continental lithosphere is typically about 200 km (120 mi) thick, though this varies considerably between basins, mountain ranges, and stable cratonic interiors of continents. The location where two plates meet

16637-414: Was interpreted to be the modern Tibetan Plateau) at 25–20 Ma. This hypothesis is mainly based on the observation of crustal shortening deficit in the Himalayas. The convergence of the Indian and Eurasian plate since the Cretaceous should have led to crustal shortening of approximately 3,600 ± 35 km. However, the observed shortening in the Himalayas and the Asian continent accounts for only 30–50% of

16768-424: Was observed early that although granite existed on continents, seafloor seemed to be composed of denser basalt , the prevailing concept during the first half of the twentieth century was that there were two types of crust, named "sial" (continental type crust) and "sima" (oceanic type crust). Furthermore, it was supposed that a static shell of strata was present under the continents. It therefore looked apparent that

16899-521: Was partially melted at that time and was bounded by a "channel" formed from the rigid upper and lower crust. The molten middle crust is thought to be represented by high-temperature rock suites in the Greater Himalayan Crystalline Complex . Since the upper crust was rather strong, the melt cannot propagate towards the surface. The second stage took place during early to mid Miocene . The South Asian monsoon developed and

17030-443: Was popularized during the 1980s and 1990s. Recent research, based on three-dimensional computer modelling, suggests that plate geometry is governed by a feedback between mantle convection patterns and the strength of the lithosphere. Forces related to gravity are invoked as secondary phenomena within the framework of a more general driving mechanism such as the various forms of mantle dynamics described above. In modern views, gravity

17161-575: Was supported in this by researchers such as Alex du Toit ). Furthermore, when the rock strata of the margins of separate continents are very similar it suggests that these rocks were formed in the same way, implying that they were joined initially. For instance, parts of Scotland and Ireland contain rocks very similar to those found in Newfoundland and New Brunswick . Furthermore, the Caledonian Mountains of Europe and parts of

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