The study authors also discovered that some splinters of Greater Adria didn't subduct under Europe and instead remained above sea level.
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Why it matters: New simulations suggest the icy shell is broken into segments that shift, flex, and subduct, just like the Earth's crust.
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At Taitao, the Chile Triple Junction and the Nazca Plate subduct the South American Plate.
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To accommodate the compression of the Somali plate due to two extensional edges of the plate the oceanic plate might begin to subduct below the continental plate.
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The hot, positively buoyant ocean crust from the extension won't subduct, instead obducting onto the island arc as an ophiolite. As compression persists, the ophiolite is emplaced onto the continental margin.
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Once oceanic plates subduct in the lower mantle (slabs), they are assumed to sink in a near- vertical manner. With the help of seismic wave tomography, this can be used to constrain plate reconstructions at first order back to the Permian.
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Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography. The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction. At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan. As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time.
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The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction. At first, the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction was located near the Strait of Magellan. As the southern part of the Nazca Plate and the Chile Rise became consumed by subduction, the more northerly regions of the Antarctic Plate began to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time. The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of c.
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As the Antarctic—South American plate motion changed from north to north-west during this period, oceanic crust in the north-west Weddell Sea started to subduct on the eastern side of the Drake land bridge—the eastward migration of the South Sandwich Trench had begun.
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Some lithospheric plates consist of both continental and oceanic lithosphere. In some instances, initial convergence with another plate will destroy oceanic lithosphere, leading to convergence of two continental plates. Neither continental plate will subduct. It is likely that the plate may break along the boundary of continental and oceanic crust.
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The Pacific Plate is the largest known plate on Earth. It is considered an oceanic plate because it is much more dense than a continental plate. That is the reason why oceanic plates always subduct under another plate. There are only a few places where the Pacific Plate is actually above the ocean.
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Together with the Tonga Trench to the north, it forms the -long, near-linear Kermadec-Tonga subduction system, which began to evolve in the Eocene when the Pacific Plate started to subduct beneath the Australian Plate. Convergence rates along this subduction system are among the fastest on Earth, /yr in the north and /yr in the south.
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The debris from the continental arc would deposit in the subduction zone as turbidite. The undergoing subduction forces sediments to accretively add to the accretionary wedge or to subduct into the asthenosphere. Then part of sediments would be recycled through volcanic activities, and thus return to the continental crust, while another part would form new mantle material.
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Some geologists believe some fundamental change in convection within the Earth's mantle caused the rifting event, while others believe the huge oceanic plate became mechanically unstable as it continued to subduct beneath the Pacific Northwest. The Kula Plate once again continued to subduct beneath the continental margin, supporting the Coast Range Arc. Volcanism began to decline along the length of the arc about 60 million years ago during the early Paleogene period of the Cenozoic era as the rapid northern movement of the Kula Plate became parallel with the Pacific Northwest, creating a transform fault plate boundary similar to the Queen Charlotte Fault. During this passive plate boundary, the Kula Plate began subducting underneath Alaska and southwestern Yukon at the northern end of the arc during the early Eocene period.
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Orogeny is the process of mountain building. Subducting plates can lead to orogeny by bringing oceanic islands, oceanic plateaus, and sediments to convergent margins. The material often does not subduct with the rest of the plate but instead is accreted (scraped off) to the continent, resulting in exotic terranes. The collision of this oceanic material causes crustal thickening and mountain-building.
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Order of subduction control the geometry of divergent doubled subduction. The side that begins to subduct earlier enters the eclogitization level earlier. The density contrast between the plate and the mantle increases which makes the sinking of the plate faster, creating a positive feedback. It results in an asymmetrical geometry where the slab length is longer on the side which subducts earlier.
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Roughly 30 Mya the Farallon Plate subducted beneath the North American Plate, segmenting the Pacific Farallon Ridge. This subduction created new microplates and new ridges, including the Juan de Fuca Plate and Juan de Fuca Ridge. As the Juan de Fuca Plate continued to subduct underneath the North American Plate it also segmented, creating the Gorda Plate and Gorda Ridge.
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Deep plumes of mantle rock reached the surface, interacting with seawater to become serpentinite. Central Europe formed the northwestern margin of the Penninic Ocean. Permian and Triassic sediments emerged above sea level on the Moldanubian, Moravian, Helvetic and Sub-Penninc superunits. As the Tethys Ocean crust began to subduct, only small fragments of its crust remained in the Meliatic Superunit in the Eastern Alps.
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The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene epoch. At first it subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan. As the southern part of the Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate began to subduct beneath Patagonia so that the Chile Triple Junction lies at present in front of Taitao Peninsula at 46°15' S. The subduction of the Antarctic Plate beneath South America is held to have uplifted Patagonia as it reduced the previously vigorous down-dragging flow in the Earth's mantle caused by the subduction of the Nazca Plate beneath Patagonia. The dynamic topography caused by this uplift raised Quaternary-aged marine terraces and beaches across the Atlantic coast of Patagonia.
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The Kula Plate is an ancient tectonic plate that used to subduct under Alaska.Steinberger, Bernhard, and Carmen Gaina Geology 35 (5) 407-410, 2007 Plate-tectonic reconstructions predict part of the Hawaiian hotspot tract to be preserved in the Bering Sea On 18 December 2018, a large meteor exploded above the Bering Sea. The space rock exploded with 10 times the energy released by the Hiroshima atomic bomb.
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The triple junctions in the New England region stopped subduction very quickly because the mid ocean ridge was almost parallel to the trench. The merger converted the trench to a transform fault and turned off the volcanoes to the west. In between these two ridge trench encounter points, a small triangular shaped plate continued to subduct between Brisbane and Coffs Harbour. More time was available to build up a wide subduction complex.
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The strong lithosphere of the indenter remains relatively undeformed and its boundaries are preserved, while the host allows deformation by lateral movement of crust both along the contact with the indenter and within the host. The indenter block is too buoyant to subduct, so crustal accommodation is achieved by either shallow underthrusting and crustal thickening, or formation and later lateral displacement of several microplates. It is possible to have a combination of the two models.
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Around 200 million years ago, the ancient oceanic Farallon Plate began to subduct beneath the North American Plate. As the Farallon moved eastward, it was overridden by the North American, and the moisture within it was figuratively baked out of the rock before the crust melted into magma. As it began to cool, a large mass of igneous rock was created and is now visible as the granite domes of the Sierra Nevada Batholith.Nahler, Nathan.
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The principal difference between the two planets is the lack of evidence for plate tectonics on Venus, possibly because its crust is too strong to subduct without water to make it less viscous. This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field. Instead, Venus may lose its internal heat in periodic major resurfacing events.
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The Cascade Arc was originally created by subduction of the now vanished Farallon Plate at the Cascadia subduction zone. After 28 million years ago, the Farallon Plate segmented to form the Juan de Fuca Plate, which continues to subduct under the Pacific Northwest of North America. In the last few million years, volcanism has declined along the volcanic arc. The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates.
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The history of this basin begins with the subduction of Pacific plate underneath the North American plate in the beginning of the Mesozoic. During this subduction event, two smaller plates, the Monterey and Juan de Fuca plates, also began to subduct underneath the North American plate. Around 20Ma, the Monterey plate attached to and followed the motion of the Pacific plate. Later, subduction of the Pacific-Monterey ceased and the plate margin was converted to a transform boundary.
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South of New Zealand the boundary becomes a transitional transform-convergent boundary, the Macquarie Fault Zone, where the Australian Plate is beginning to subduct under the Pacific Plate along the Puysegur Trench. Extending southwest of this trench is the Macquarie Ridge. The southerly side is a divergent boundary with the Antarctic Plate called the Southeast Indian Ridge (SEIR). The subducting boundary through Indonesia is not parallel to the biogeographical Wallace line that separates the indigenous fauna of Asia from that of Australasia.
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Subduction at the Mariana plate has been going on for over 50 million years. Some theories of the origin of this microplate is that when the Pacific plate began to subduct beneath the Philippine plate the volcanism and spreading ridge started to make an arc. This geological activity caused the section of the Philippine plate to break off and become the Mariana microplate. The Mariana Islands consist of volcanoes that are active and dormant and are made up of volcanic and sedimentary rocks from the Pleistocene.
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The separation from Antarctica changed the tectonics of the Fuegian Andes into a transpressive regime with transform faults. About 15 million years ago in the Miocene the Chile Ridge begun to subduct beneath the southern tip of Patagonia (55° S). The point of subduction, the triple junction has gradually moved to the north and lies at present at 47° S. The subduction of the ridge has created a northward moving "window" or gap in the asthenosphere beneath South America.Charrier et al. 2006, p. 112.
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A tectonostratigraphic terrane is not necessarily an independent microplate in origin, since it may not contain the full thickness of the lithosphere. It is a piece of crust which has been transported laterally, usually as part of a larger plate, and is relatively buoyant due to thickness or low density. When the plate of which it was a part subducted under another plate, the terrane failed to subduct, detached from its transporting plate, and accreted onto the overriding plate. Therefore, the terrane transferred from one plate to the other.
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In the Cretaceous period the Piemont-Liguria Ocean lay between Europe (and a smaller plate called the Iberian plate) in the northwest and the Apulian plate (a sub-plate of the African tectonic plate) in the southeast. When the Apulian plate started moving to the northwest in the late Cretaceous, Piemont-Ligurian crust began to subduct beneath it. In the Paleocene the Piemont-Ligurian Ocean had completely disappeared under the Apulian plate and continental collision started between Apulia and Europe, which would lead to the formation of the Alps and the Apennines in the Tertiary.
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The ridge is a medium rate spreading center, moving outwards at a rate of approximately 6 centimeters per year. Tectonic activity along the ridge is monitored primarily with the U.S. Navy's Sound Surveillance System (SOSUS) array of hydrophones, allowing for real time detection of earthquakes and eruptive events. The Juan de Fuca Plate is being pushed east underneath the North American Plate, forming what is known as the Cascadia subduction zone off the coast of the Pacific Northwest. The plate does not subduct smoothly and can become 'locked' with the North American plate.
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West of South America, the Nazca Plate and the Antarctic Plate subduct beneath the South America Plate at a rate of , giving rise to the Andean volcanic belt. The volcanic belt is not continuous and is interrupted by gaps where the subduction is shallower and the asthenosphere between the two plates missing. North of the Payún Matrú, flat slab subduction takes place; in the past flat slab subduction occurred farther south as well and had noticeable influence on magma chemistry. In general, the mode of subduction in the region over time has been variable.
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This collision also crushed and folded sedimentary and igneous rocks, creating a mountain range called the Kootenay Fold Belt which existed in far eastern British Columbia. Plate tectonics of the Omineca and Insular arcs 130 million years ago. After the sedimentary and igneous rocks were folded and crushed, it resulted in the creation of a new continental shelf and coastline. The Insular Plate continued to subduct under the new continental shelf and coastline about 130 million years ago during the mid Cretaceous period after the formation of the Intermontane Belt, supporting a new continental volcanic arc called the Omineca Arc.
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They used the terms 'Paleotethys', 'Mesotethys', and 'Neotethys' for the Caledonian, Variscan, and Alpine orogenies, respectively. In the 1970s and '80s, these terms and 'Proto- Tethys', were used in different senses by various authors, but the concept of a single ocean wedging into Pangea from the east, roughly where Suess first proposed it, remained. In the 1960s, the theory of plate tectonics became established, and Suess's "sea" could clearly be seen to have been an ocean. Plate tectonics provided an explanation for the mechanism by which the former ocean disappeared: oceanic crust can subduct under continental crust.
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In the situation where a spreading ridge approaches a subduction zone, the ridge collides with the subduction zone, at which time there will develop a complex interaction of subduction-related tectonic sedimentary, and spreading-related tectonic igneous activity. The left-over ridge may either subduct or ride upward across the trench onto arc trench gap and arc terranes as a hot ophiolite slice. These two mechanisms are shown in figure 2 B and C. Two examples of this interaction of a ridge colliding into a trench are well documented. The first one is the progressive diminution of the Farallon plate off California.
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At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan. As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced gradually to its present position in front of Taitao Peninsula at 46°15’. Taitao Peninsula lies near the triple junction and various geological features, such as the Taitao ophiolite, are related to the dynamics of the triple junction.
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The Chile Triple Junction (or Chile Margin Triple Junction) is a geologic triple junction located on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula on the southern coast of Chile. Here three tectonic plates meet: the South American Plate, the Nazca Plate, and the Antarctic Plate. This triple junction is unusual in that it consists of a mid-oceanic ridge, the Chile Rise, being subducted under the South American Plate at the Peru–Chile Trench. The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene epoch forming the Chile Triple Junction.
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Prior to Garibaldi Belt formation, a number of older, but related volcanic belts were constructed along the Southern Coast of British Columbia. This includes the east-west trending Alert Bay Volcanic Belt on northern Vancouver Island and the Pemberton Volcanic Belt along the coastal mainland. The Pemberton Belt began its formation when the former Farallon Plate was subducting under the British Columbia Coast 29 million years ago during the Oligocene epoch. At this time, the north-central portion of the Farallon Plate was just starting to subduct under the U.S. state of California, splitting it into northern and southern sections.
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Others argue that the subcontinental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosion and subsequent tectonic events. In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island rocks and deposited in a forearc basin.
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Simultaneously, the vast Tethyn oceanic crust, to its northeast, began to subduct under the Eurasian plate. These dual processes, driven by convection in the Earth's mantle, both created the Indian Ocean and caused the Indian continental crust eventually to under-thrust Eurasia and to uplift the Himalayas. The rising barriers blocked the paths of rivers creating large lakes, which only broke through as late as 100,000 years ago, creating fertile valleys in the middle hills like the Kathmandu Valley. In the western region, rivers which were too strong to be hampered, cut some of the world's deepest gorges.
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These differences result from processes that occur during the subduction of oceanic crust and mantle lithosphere. Oceanic crust (and to a lesser extent, the underlying mantle) typically becomes hydrated to varying degrees on the seafloor, partly as the result of seafloor weathering, and partly in response to hydrothermal circulation near the mid-ocean-ridge crest where it was originally formed. As oceanic crust and underlying lithosphere subduct, water is released by dehydration reactions, along with water-soluble elements and trace elements. This enriched fluid rises to metasomatize the overlying mantle wedge and leads to the formation of island arc basalts.
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In the Middle Miocene, the Pacific-Farallon Ridge was subducted beneath North America ending subduction along this part of the Pacific margin; however, the Farallon Plate continued to subduct into the mantle. The movement at this boundary divided the Pacific- Farallon Ridge and spawned the San Andreas transform fault, generating an oblique strike-slip component. Today, the Pacific Plate moves north-westward relative to North America, a configuration which has given rise to increased shearing along the continental margin. The tectonic activity responsible for the extension in the Basin and Range is a complex and controversial issue among the geoscience community.
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Compression forces, coupled with the inability of the thin basaltic crust to subduct, resulted in fold mountains around the edges of Ishtar. Further compression led to underthrusting of material that subsequently was able to partially melt and feed volcanism in the central plateau. If the directional evolution model is valid then the evolution must have been slow and the timing of events would have overlapped considerably. A valid end member interpretation is that the crater population still represents a population emplaced on a mostly inactive planet, but the final throes of a global emplacement of volcanic plains has filled most of the craters with a few hundred meters of volcanic flows.
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The subduction of the Pacific Plate beneath the Australia Plate has given rise to volcanic and hydrothermal activity on the Kermadec Ridge that Monowai is part of. The volcano is located at the site where the Osbourn Trough and the Louisville seamount chain subduct in the Tonga Trench and this subduction process probably has influenced its volcanism. Monowai is one of the most active volcanoes in the Kermadec volcanic arc, with many eruptions since 1977, and perhaps the most active submarine volcano in the world. Volcanic activity is characterised by the emission of gas and discolouration of water, along with seismic activity and a substantial growth rate of the volcano.
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India accounts for the bulk of the Indian subcontinent, lying atop the Indian tectonic plate, a part of the Indo-Australian Plate. India's defining geological processes began 75 million years ago when the Indian Plate, then part of the southern supercontinent Gondwana, began a north- eastward drift caused by seafloor spreading to its south-west, and later, south and south-east. Simultaneously, the vast Tethyan oceanic crust, to its northeast, began to subduct under the Eurasian Plate. These dual processes, driven by convection in the Earth's mantle, both created the Indian Ocean and caused the Indian continental crust eventually to under-thrust Eurasia and to uplift the Himalayas.
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This collision crushed and folded sedimentary and igneous rocks, creating a mountain range called the Kootenay Fold Belt which existed in far eastern Washington State and British Columbia. After the sedimentary and igneous rocks were folded and crushed, it resulted in the creation of a new continental shelf and coastline. This coastline and continental shelf was located adjacent to the eastern margin of Methow Valley. The Insular Plate continued to subduct under the new continental shelf and coastline about 130 million years ago during the mid Cretaceous period after the formation of the Intermontane Belt, supporting a new continental volcanic arc called the Omineca Arc.
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This large mass of igneous rock is the largest granite outcropping in North America. Plate tectonics of the Coast Range Arc 100 million years ago. The Farallon Plate continued to subduct under the new continental margin of Western Canada after the Insular Plate and Insular Islands collided with the former continental margin, supporting a new chain of volcanoes on the mainland of Western Canada called the Coast Range Arc about 100 million years ago during the Late Cretaceous epoch. Magma ascending from the Farallon Plate under the new continental margin burned their way upward through the newly accreted Insular Belt, injecting huge quantities of granite into older igneous rocks of the Insular Belt.
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The Nazca Plate or Nasca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Nazca Plate under the South American Plate is largely responsible for the Andean orogeny. The Nazca Plate is bounded on the west by the Pacific Plate and to the south by the Antarctic Plate through the East Pacific Rise and the Chile Rise respectively. The movement of the Nazca Plate over several hotspots has created some volcanic islands as well as east-west running seamount chains that subduct under South America.
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Due to the flow in the lower mantle causing slab suction, changes in viscosity will have a much different effect than how it would apply to the upper mantle. In the lower mantle if you have a decrease in viscosity the flow will become much more rapid and increase the effect of slab suction and if viscosity in the lower mantle increases the effects of slab suction will decrease. Associated with the slab suction force is the idea of trench roll- back. As a slab of oceanic crust subducts into the mantle, the hinge of the plate (the point where the plate begins to subduct) tends to regress away from the trench.
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The final event began when the Farallon Plate continued to subduct under the new continental margin after the Insular Plate and Insular Islands collided with the old continental margin, supporting a new continental volcanic arc called the Coast Range Arc about 100 million years ago during the Late Cretaceous period. Magma rising from the Farallon Plate under the new continental margin ascended through the newly accreted Insular Belt, injecting huge quantities of granite into older igneous rocks of the Insular Belt. At the surface, new volcanoes were built along the continental margin. Named after the Coast Mountains, the basement of this arc was likely Early Cretaceous and Late Jurassic intrusions from the Insular Islands.
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On the western margin of South America, the Peru-Chile Trench separates the South America Plate from the plates of the Pacific Ocean and marks the site where these plates subduct beneath South America. The subduction of the Nazca Plate beneath the South America Plate causes the volcanic phenomena of the Central Volcanic Zone as well as geothermal phenomena in northern Chile such as at El Tatio, Puchuldiza and Surire. The region contains ignimbrites and other volcanic rocks that were erupted during the Miocene to Pleistocene overlying earlier sediments and volcanites; these deposits appear to contain the hydrothermal systems. Geothermal phenomena are widespread and occur in the form of fumaroles, geysers, hot springs and mud pools.
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Structure of the Cascadia subduction zone As the last of the Kula Plate decayed and the Farallon Plate advanced back into this area from the south, it once again started to subduct under the continental margin of Western Canada 37 million years ago, supporting a chain of volcanoes called the Cascade Volcanic Arc. At least four volcanic formations along the British Columbia Coast are associated with Cascadia subduction zone volcanism. The oldest is the eroded 18-million- year-old Pemberton Volcanic Belt which extends west-northwest from south- central British Columbia to the Queen Charlotte Islands in the northeast where it lies west of mainland British Columbia. In the south it is defined by a group of epizonal intrusions and a few erosional remnants of eruptive rock.
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The Giant Staircase between Yosemite and Little Yosemite Valley When the North American Plate on its slow journey westwards encountered the Pacific Plate approximately 250 million years ago during the Paleozoic, the latter began to subduct under the North American continent. Intense pressure underground caused some of the Pacific Plate to melt, and the resulting upwelling magma pushed up and hardened into the granite batholith that makes up much of the Sierra Nevada. Extensive layers of marine sedimentary rock that originally made up the ancient Pacific seabed were also pushed up by the rising granite, and the ancestral Merced River formed on this layer of rock. Over millions of years, the Merced cut a deep canyon through the softer sedimentary rock, eventually hitting the hard granite beneath.
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The CLIP drifted into the same area, but as it was less dense and thicker than the surrounding oceanic crust, it did not subduct, but rather overrode the ocean floor, continuing to move eastward relative to North America and South America. With the formation of the Isthmus of Panama 3 million years ago, it ultimately lost its connection to the Pacific. The more recent theory asserts that the Caribbean Plate came into being from an Atlantic hotspot which no longer exists. This theory points to evidence of the absolute motion of the Caribbean Plate which indicates that it moves westward, not east, and that its apparent eastward motion is only relative to the motions of the North American Plate and the South American Plate.
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Volcanoes in the Andes occur in four separate regions: the Northern Volcanic Zone between 2°N and 5°S, the Central Volcanic Zone between 16°S and 28°S, the Southern Volcanic Zone between 33°S and 46°S, and the Austral Volcanic Zone, south of the Southern Volcanic Zone. These volcanic zones are separated by areas where recent volcanism is absent; one common theory is that the subduction processes responsible for volcanism form a subducting plate that is too shallow to trigger the formation of magma. This shallow subduction appears to be triggered by the Nazca Ridge and the Juan Fernandez Ridge; the areas where they subduct beneath the Peru-Chile Trench coincide with the limits of the Central Volcanic Zone. It is possible that when these ridges are subducted, the buoyancy they carry disrupts the subduction process and reduces the supply of water, which is important for the formation of melts.
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The Nazca Plate and Antarctic Plate subduct beneath the South America Plate in the Peru-Chile Trench at a pace of and , respectively, resulting in volcanic activity and geothermal manifestations in the Andes. Present-day volcanism occurs within four discrete belts: the NVZ (between 2°N–5°S), the CVZ (16°S–28°S), the SVZ (33°S–46°S) and the Austral Volcanic Zone (AVZ) (49°S-55°S). Between them they contain about 60 active volcanoes and 118 volcanoes which appear to have been active during the Holocene, not including potentially active very large silicic volcanic systems or very small monogenetic ones. These belts of active volcanism occur where the Nazca Plate subducts beneath the South America Plate at a steep angle, while in the volcanically inactive gaps between them the subduction is much shallower; thus there is no asthenosphere between the slab of the subducting plate and the overriding plate in the gaps.
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The lavas of the Louisville Seamount Chain were generated 80-90 Ma but began to subduct under the Tonga-Kermadec Ridge at 8 Ma. The Hikurangi and Manihiki plateaux, north and south of the Tonga-Kermadec Ridge respectively, form part of the Ontong Java-Hikurangi-Manihiki large igneous province (LIP), the largest volcanic event on Earth during the past 200 million years. The Osbourn Trough, located just north of the Tonga-Kermadec and Louisville intersection, is the palaeo-spreading centre between the Hikurangi and Manihiki plateaux away from which the age of the Pacific Plate increases from 85 Ma to 144 Ma. The subduction of the Hikurangi Plateau beneath New Zealand and the southern part of the Kermadec Arc has resulted in large volumes of lava and a high density of volcanoes in the arc. The initial Hikurangi-Kermadec collision, however, occurred to the north where a missing piece of the Ontong Java-Hikurangi- Manihiki LIP has already been subducted.
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