Because subduction zones are typically located along coastlines, the resulting earthquakes caused by the tectonic plate movement often cause tsunami waves to ravage coastal environments and urban settlements. This paper briefly reviews the magmatic manifestations of volcanic arcs and aspects of how such magmas form. Answer to: How does subduction create volcanoes? An island arc results when one oceanic plate moves under another oceanic plate. Earthquakes are well-known geological phenomena, usually caused when two pieces of the Earth’s crust, called tectonic plates, bang or rub against each other. The explanation of subduction perhaps makes the process sound relatively smooth, with one plate slowly sinking and falling off into the mantle layer below. … Smaller plate boundaries typically generate smaller tremors. Most scientists, however, describe subduction as a rough, scraping activity that is characterized by high amounts of friction as the two plates rub past each other. Although tectonic plates may be oceanic or continental, the act of subduction (sliding under another plate) only happens to oceanic plates. Flux melting: Wherever water (or other volatiles like carbon dioxide or sulfur gases) can be stirred into a body of rock, the effect on melting is dramatic. Subduction generates strong thermal and chemical disequilibrium, which causes mineral transformations, slab devolatilization, melting and perturbations of mantle flow. Where two tectonic plates converge, if one or both of the plates is oceanic lithosphere, a subduction zone will form. Note: the volcanic arc lies where the Benioff Zone earthquakes are around 100 km beneath the surface but Benioff zone earthquakes continue past this, landward down to 60 km; therefore the slab has not melted away. The subduction zone, accordingly, is the antithesis of the mid- oceanic ridge. the breakdown of lawsonite releases massive amounts of H2O into the mantle that can trigger partial melting of the slab and of the overlying mantle. As the subducting plate moves under its neighboring tectonic plate, gravity pushes it further down and into the mantle layer of the earth. Mid-Oceanic Ridge (MOR) is the place where magma from below the Earth emerges an… Why exactly does this geological process occur? This movement causes the overall temperature of the oceanic lithosphere to drop, which serves to solidify material found on the underneath side of the plate. This ring moves along the western coastlines of the Americas and along the eastern coastlines of Asia and the Pacific Islands, forming an upside down u-shape. There are 2 main types of subduction zones: Oceanic-oceanic plate boundaries: If the subducting plate subducts beneath an adjacent oceanic plate, an island arc is formed. At depths of around 100 km beneath the surface, the pressure is great enough for the hydrous minerals to undergo metamorphism. How does subduction trigger melting? The subduction/collision transition Reference Hoareau 109 illustrates how quickly the reorganization of Earth’s tectonic building blocks may cause imbalances in the geological C cycle (Figure 10.5). The addition of water to the already hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to yield mafic magma. The subduction process is credited with being the single, largest contributor behind the theory of plate tectonics. Subduction is a geological process in which oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries.Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. When two plates move apart, they create a space that can be filled by hot rock that rises buoyantly from below. The overriding slab insulates the subducting slab, increasing temperature and causing melting. The reason for this is that oceanic plates, also known as the oceanic lithosphere, start out as thin and hot sections of earth. /Earth Planetary Science letters 121 (1994) 227-244 subduction shear zone exceeds the temperature of the partial melting reactions (~ 750 at 2.5 GPa). Introduction. Remember, oceanic plates are formed from mantle material at midocean ridges. Although the process is not clearly understood,… Now this process is a process of partial melting. Beneath the active volcanic arc lie intrusive igneous rocks formed from magma that didn't make it all the way to the surface before crystallizing. Benioff Zones:  Earthquakes in and around deep ocean trenches are principally produced by motions on thrust faults, indicating compression (converging plates). A plane of earthquake focci descend from the area around the trench underneath the overriding plate. a) Slab-mantle interaction; b) Steady-state condition of subduction with the slab lying on the 660 km discontinuity. These subduction zone-created volcanoes occur in one of two formations: island arc or continental arc. This trend is strongest in subduction zone volcanism. Continental crust, chemically, tends to have more felsic mineralogical composition than oceanic one. This melted material is known as magma or lava. As the subducting slab moves under the less dense plate, some of its pieces may become caught on the upper plate. Three-quarters of the volcanic activity on earth is confined to an area known as the Pacific Ring of Fire. As the descending slab sinks into the mantle it returns its carbon to deep Earth. Fluids play a critical role in subduction zones and arc magmatism. Because subduction occurs along very long plate boundary lines, the potential for a very strong earthquake increases. Volcanoes associated with subduction zones generally have steep sides and erupt explosively. Gaetani and Grove and Tatsumi show that melting in subduction zones is complicated and may occur by several processes simultaneously in the same system. At shallow levels in subduction zones (<40 kilometers depth), expulsion of large volumes of pore waters and CH4-H2O fluids produced by diagenetic and low-grade metamorphic reactions affect the thermal and rheological evolution of the accretionary prism and provide nutrients for deep-sea biological communities. The crust sticks in some places, storing up energy that is released in earthquakes. Although this process is generally attributed to the movement of tectonic plates, some geologists have theorized that very old plates may sink quickly and without warning given their significantly denser state. Aside from triggering mantle melt, this reaction may also trigger partial melting of the subducting slab itself. Tsunamis, large and dangerous waves, are the result of earthquakes (and other geologic activity) on or near coastlines. Subduction occurs very slowly. This solidification process causes the resulting solid rock to shrink (compared to its original size when liquid), leading to its increased density. If the subduction occurs between two oceanic plates, it is the older plate that will move underneath the younger tectonic plate. This metamorphic dewatering process liberates water from the descending crust. See pencast sketch of decompression melting at a midocean ridge! Geologists rely on this zone to extract valuable information concerning the link between subduction zones, volcanoes, and earthquakes. Scientists have confirmed a positive correlation between the size of a fault line and the size of an earthquake. This accounts for the copious volcanism near subduction zones, where descending plates carry down water, sediment, carbonaceous matter and hydrated mineral with them. stretching the oceanic crust C.) a decrease in pressure D.) … Some examples of this include the Great Chilean Earthquake of 1960 (a magnitude of 9.5), the Indian Ocean Earthquake of 2004 (a magnitude of between 9.1 and 9.3), and the Japanese Tohoku Earthquake of 2011 (a magnitude of between 9 and 9.1). the breakdown of lawsonite releases massive amounts of H2O into the mantle that can trigger partial melting of the slab and of the overlying mantle. When the older plate is holding a continent however, it does not sink, which is reassuring. Thus, subduction zones process inputs (subducted material and incoming asthenosphere) to generate outputs (volcanic products, residues expelled to the deep mantle) by performing mechanical and chemical work. In this set of experiments, partial melting of subducting oceanic crust will only occur if the temperature of the brittle-plastic transition in the 238 S.M. Another side effect of the subduction process is the creation of volcanoes, as well as increased volcanic activity above subduction zones. Volcanic Arcs:  The basaltic ocean crust contains hydrous minerals like amphiboles, some of which formed by hydrothermal alteration as seawater seeped through hot, fractured, young ocean crust at the midocean ridge. Some of the largest fault lines (by both width and length) in the world are located at subduction zones. Tsunamis may occur over a period of just a few minutes or even hours, as the displaced water rushes onto nearby land. An oceanic plate will sink back into the mantle. This wave activity occurs because earthquakes cause the crust of the earth to snap and rebound. C. Flux melting of the asthenosphere above the … When two oceanic plates meet, the older plate subducts. In geological terms, subduction is the act of one tectonic plate moving under another tectonic plate at the point of their convergent boundary. What Happens During the Process of Seafloor Spreading. A.) Melting aided by the addition of water or other fluid is called flux melting. The water gradually seeps upward into the overlying wedge of hot mantle. Phlogopite + Diopside + Orthopyroxene = H 2 O + Melt [1] Lawsonite remains stable up to 1080 °C and 9.4 GPa. Shoving two massive slices of Earth's crust together is like rubbing two pieces of sandpaper against each other. This density causes the plate to sink under continental plates or younger, less dense, oceanic plates. They occur down to depths of around 670 km at some subduction zones. Geologists explain that subduction occurs to oceanic plates because they are denser and cooler than continental plates. melting of mantle-wedge peridotite exert the main controls on melt pro-duction in volcanic arcs. Many mountain ranges around the world were created in this manner. There is a deep ocean trench where the oceanic plate bends downward. Subduction occurs when two plates collide and one plunges beneath the other. Subduction zone, oceanic trench area marginal to a continent in which, according to the theory of plate tectonics, older and denser seafloor underthrusts the continental mass, dragging downward into the Earth’s upper mantle the accumulated trench sediments. Subduction zones form where a plate with thinner (less-buoyant) oceanic crust descends beneath a plate with thicker (more-buoyant) continental crust. As the subducting plate moves under its neighboring tectonic plate, gravity pushes it further down and into the mantle layer of the earth. A continental arc results when an oceanic plate moves under a continental plate. The largest earthquakes ever recorded were on subduction zones, such as a magnitude 9.5 in Chile in 1960 and a magnitude 9.2 in Alaska in 1964. The volcanic arcs may be volcanic island arcs (e.g., Aleutians, Mariannas), where one oceanic plate subducts beneath another oceanic plate, or continental volcanic arcs (e.g., Andes, Cascades), where oceanic plates subduct under a continental plate. The process of dehydration that ultimately triggers melting beneath subduction zones must occur approximately beneath the arc such that the mechanism for fluid transfer is rapid and probably vertical. The resulting minerals are denser and they don't contain the bonded water. Volcanoes and volcanic activity often occur as a result of the subduction process because the subducting slab releases liquids as it moves into the extreme temperatures of the mantle layer. Without this (and the plate tectonics that drive it) there would be no differentiated continental crust! The place where subduction has occurred, however, does not result in the formation of mountains. Other articles where Subduction volcano is discussed: volcano: Subduction volcanoes: As an oceanic plate is subducted beneath a continental plate, seafloor sediments rich in water and carbon dioxide are carried beneath the overriding plate. This speed is slow enough that subduction often goes unnoticed. At a subduction zone, melting is triggered by what? Upon reaching a subduction zone, the sinking plate heats up and gets squeezed, resulting in the gradual release of some or all of its water. convergent tectonic plate boundaries or where two tectonic plates come crashing together This obstacle results in spent up energy that can only be released in one way: earthquakes. These extremely hot liquids, which primarily consist of carbon dioxide and ocean water, effectively melt the plate that has remained on top. In addition to earthquakes and volcanic activity, the process of subduction is also credited with causing severe tsunamis around the world. The hotter temperatures and increased pressure found at these depths cause the basalt rock of the sinking plate, also referred to as a slab, to morph into eclogite rock. Magma generation is driven by lithospheric extension, which triggers shallow decompression melting (1300 o C) of dry upper mantle peridotite (≪100 km). Oceanic lithosphere is formed hot and thin at mid-ocean ridges and grows thick as more rock hardens underneath it. As the ocean crust sinks deeper into the mantle the pressure increases (the temperature of the ocean crust rocks increases more slowly because rocks are poor conductors of heat). The mantle layer is hotter than the crust, although it is generally found in a solid state, and allows the subducting plate to sink at angles of between 25 and 45 degrees. A. Continental and oceanic crust makes up nearly three-fourths of the Earth’s body, providing sources of sediment and basement of basins. In fact, the largest earthquakes ever recorded all occurred at subduction zones. The exact angle of the subduction depends on the age of the subducting plate; older plates fall at a sharper angle. As previously mentioned, an oceanic plate is the only tectonic plate that actually experiences subduction, or downward, movement. Over time, these plates gradually move away from the mid-ocean ridge where they were born. How does magma behave? It is somewhat more complicated than this, but metamorphic dewatering of suducting crust and flux melting of the mantle wedge appears to account for most of the magma at subduction zones. Knowing what subduction is, does not explain why it happens. In addition to causing earthquakes, subduction can also trigger tsunamis. The most abundant igneous rock formed at volcanic arcs is andesite (or intrusive diorite), though volcanic arc rocks may range in composition from basalt to rhyolite (mafic to felsic). One plate containing oceanic lithosphere descends beneath the adjacent plate, thus consuming the oceanic lithosphere into the earth's mantle. Figure 4: Cartoons showing scenarios able to trigger decompression melting produced by slab return flow, and the resulting development of off-axis volcanism. Rocks shrink as they cool, so the plate becomes more dense and sits lower than younger, hotter plates. The two plates are Oceanic plate and Continental plate. In particular, they explore how the melting and movement of glaciers, such as that caused by human-induced climate change, can trigger earthquakes. In addition, adia- Peacock et al. Trenches, accretionary wedges (prisms) and volcanic or island arcs are key surface features produced by subduction. Visualising Earthquakes. The reason for these extreme earthquake magnitudes is attributed solely to the size of the fault line. The massive scale of subduction zones means they can cause enormous earthquakes. Examples include the Aleutians, the Kuriles, Japan, and the Philippines, all located at the northern and western borders of the Pacific plate. The mantle layer is hotter than the crust, although it is generally found in a solid state, and allows the subducting plate to sink at angles of between 25 and 45 degrees. These compounds may act as fluxes, reducing the melting temperature of magma. The Earth’s crust triggers the questions of Earth scientists regarding its formation and evolution through time. Young oceanic lithosphere is hot and buoyant (low density) when it forms at a midocean ridge. A subduction zone is the entire area of subduction between the trench and the volcanic arc. This sudden movement on the ocean floor results in displaced water, which moves toward the shore in extremely high and long waves. Phlogopite + Diopside + Orthopyroxene = H 2 O + Melt [1] Lawsonite remains stable up to 1080 °C and 9.4 GPa. Melting aided by the addition of water or other fluid is called flux melting. In fact, geologists have identified the average rate of convergence at between 2 and 8 centimeters per year. Divergent plate boundary displays the phenomenon of sea-floor spreading. Remember that flux melting refers to the process whereby the addition of the volatile to an already hot rock will cause a hot solid rock to start to melt. The addition of water to the already hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to yield mafic magma. Why are the subduction zone volcanoes so steep? Subduction zones produce volcanic arcs, curving chains of steep-sided volcanoes, for example the Aleutian Islands in Alaska. Similarly, lithospheric extension within continental regions produces somewhat different basaltic magmas and compositionally distinct silicic and potassic magmas because of the involvement of continental lithosphere. At convergent boundaries, the process of subduction pushes lithosphere from one plate beneath the other. (Modified from Lillie, 2005.) Common concepts about “how subduction zones work” are reassessed—with particular emphasis on the atypical Cascades volcanic arc. When melting first occurs, it happens at the peripheries of individual crystal grains (b - right), yielding minute pockets of magma. The water gradually seeps upward into the overlying wedge of hot mantle. The farther from the trench, the deeper the earthquakes are. All maps, graphics, flags, photos and original descriptions © 2020 worldatlas.com. The movement of continental and oceanic plates does not go unnoticed on the surface of the earth. But as it spreads away from the ridge and cools and contracts (becomse denser) it is able to sink into the hotter underlying mantle. By Amber Pariona on March 6 2018 in Environment. Subduction is one of the two major processes of plate tectonics, the other being seafloor spreading. Flux of H 2O from the slab may trigger melting deep in the mantle wedge. In geological terms, subduction is the act of one tectonic plate moving under another tectonic plate at the point of their convergent boundary. Decompression melting occurs at mid-ocean ridges. Aside from triggering mantle melt, this reaction may also trigger partial melting of the subducting slab itself. B. the introduction of water B.) The volatiles that enter the asthenosphere trigger flux melting in the asthenosphere. By signing up, you'll get thousands of step-by-step solutions to your homework questions. As it moves away from the ridge, it cools. At the surface, subduction zones result in arc volcanism, and during eruptions carbon and other volatiles are released into the atmosphere. Upon reaching a subduction zone, the sinking plate heats up and gets squeezed, resulting in the gradual release of some or all of its water. Subduction zones evolve, may change polarity, Reference Cooper and Taylor 108 and even vanish in complex collision zones. As long as this hot rock rises faster than the temperature can cool off, the rock can melt because the pressure is decreasing as the rock gets closer to the surface. The subducting slab is made of felsic minerals, and therefore melts at lower temperatures. The exact angle of the subduction depends on the age of the subducting pl… Let's visualize what decompression meltin… This wave activity may occur for hours after a subduction zone earthquake has been registered. These earthquakes of the Benioff Zone (or Wadati-Benioff Zone) occur near the upper surface of the descending plate (or slab). When two continental plates collide, the result is an upward movement of rock and other material. This place is known as a subduction zone. Magma formed above a subducting plate slowly rise into the overriding crust and finally to the surface forming a volcanic arc, a chain of active volcanoes which parallels the deep ocean trench. The most volcanically active belt on Earth is known as the Ring of Fire, a region of subduction zone volcanism surrounding the Pacific Ocean.Subduction zone volcanism occurs where two plates are converging on one another. enough to “sweat” fluids and initiate melting.