Pdf convergent plate boundaries and collision zones. Magma flows through cracks in earths crust and hardens. A convergent boundary is an area on earth where two or more lithospheric plates collide. This produces magma, which rises and may be erupted explosively as andesite at the surface. When one of the plates is an oceanic plate, it gets embedded in the softer asthenosphere of the continental plate, and as a result, trenches are formed at the zone of subduction. New areas are added to ocean basins at divergent margins. Convergent plate margins occur when two adjoining tectonic plates. Continental drift, sea floor spreading and plate tectonics plate tectonics is a theory developed in the late 1960s, to explain how the outer layers of the earth move and deform. Antarctica is surrounded by constructive plate boundaries. Rock uplift and exhumation of continental margins by the collision. Where continents collide, earthquakes are scattered over a much wider area compared to earthquakes along mid ocean ridges, transform margins, or subduction zones. The tectonics produced by the subduction of thousands of kilometers of ocean crust shaped the geologic record of the convergent margin, but.
The supercontinent pangea began to break up 200 ma and india started a northward drift towards asia. The magma rises through the lines of weakness to the ocean floor. Continental crust subduction zone oceanic crust backarc basin accretionary. If this occurs, subduction may stop in the collision zone and jump to another.
The creation of new ocean floor around the antarctic plate affects many areas and only some of the effects are evidenced through subduction zones the rest of the effects are seen in mountain building. Convergent margins where two adjacent neighboring plates move towards each other and one plate either dives under the other subduction zone or the two plates crumple where they collide. Often it is the older and colder plate that is denser and subducts beneath the younger and warmer plate. The volcanic activity the subduction causes the same as in oceanic continental destructive margins leads to the formation of a chain of volcanic islands like the mariana islands. Convergent plate margin dynamics research school of earth. When an oceanic plate converges with a continental plate, it is always the ocean plate that subducts beneath the continental plate. Not surprisingly, the shallowest portions of subduction zones are known best. Subduction zones have earthquakes at a range of depths, including some more than 700 km deep. The sea floor slopes into the trenches from both the landward and oceanward sides.
Part of the frontiers in earth sciences book series frontiers. World geography origin of continents and ocean basins. Cenozoic kinematics and dynamics of oblique collision between two convergent plate margins. Convergent boundary along a convergent boundary two lithospheric plates collide against each other. As the name suggests, one of the plate boundaries where one plate goes under another plate or collide with each other and gets consumeddestroyed in the process. Hkdse geographym1continentaloceanic destructive plate. Oceancontinent convergent plate boundaries chapter 1 oceancontinent convergent plate boundaries describe the activity and features of convergent plate boundaries where an oceanic plate meets a continental plate.
In fact, this area has seen the eight most powerful earthquakes ever recorded and is home to over 75 percent of the worlds active and dormant volcanoes. There are three ways in which the plates interact with each other. At an ocean ocean convergent boundary, one of the plates oceanic crust and lithospheric mantle is pushed, or subducted, under the other figure \\pageindex1\. Such destruction recycling of crust takes place along convergent boundaries where plates collide and a plate is subducted.
There are approximately 50,000 km 31,000 mi of convergent plate margins, mostly around the pacific ocean the reason for the reference pacifictype margin but they are also found in the eastern indian ocean, with relatively short convergent margin segments in the atlantic ocean and in the mediterranean sea. Convergent margin an overview sciencedirect topics. The leading edge of one plate is bent downward, as it slides beneath the other at the subduction zones. At the subduction zone, magma undergoes great pressure. Subduction zones, island arcs and active continental margins. In plate tectonics, a divergent boundary or divergent plate boundary also known as a constructive boundary or an extensional boundary is a linear feature that exists between two tectonic plates that are moving away from each other. What do you see at an ocean continent convergent boundary. In addition to the disappearance of old lithosphere, destructive boundaries associated with ocean ocean subduction and ocean continent subduction are also characterised by. The tectonic plate convergence involves movement of two plates toward each other, their collision, overriding of one plate by the edge of other plate and subduction and melting of overridden plate margin into the mantle. Continentocean convergence, formation of fold mountains. Where oceanic lithosphere meets ocean lithosphere, one plate is subducted under the other, is recycled by the mantle convection system, producing a deepsea trench.
Oceanic crust is created at the mid ocean ridges and then travels towards the subduction zones where it sinks back into the mantle. All subduction zones and the himalayas, a crumple zone, are examples of convergent margins. The nazca plate, which is thinner, denser and oceanic, is subducted under the lighter, thicker, continental south american plate into the asthenosphere, where it is melted and destroyed. Occurs when ocean crust sinks under continental crust, it sinks because its colder and denser,at these sites, deep ocean trenches also form along with. Subductioncaused volcanism and earthquake activity occur frequently along the outer edges of the pacific ocean in an area known as the pacific ring of fire. As oceanic crust moves away from the mid ocean ridges it gets colder and more dense. Most active divergent plate boundaries occur between oceanic. When a mountain belt is formed along a continental margin by subduction, sedimentary and volcanic rocks. The theory has caused a revolution in the way we think about the earth. Forced subduction initiation at passive continental margins. Deep ocean trenches are the surface manifestations produced at the subduction zones. Subduction zone and suture zone are the example of destructive plate boundary. Lines of weakness may develop because of earthquakes and other reasons.
Oceanic subduction zones dive down into the mantle beneath 55,000 km 34,000 mi of convergent plate margins lallemand, 1999, almost equal to the cumulative 60,000 km 37,000 mi of midocean ridges. Divergent plate boundarypassive continental margins. New ocean basin rift valleys formed as the thick continental crust orange ripped apart and thined. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys. Where the two plates meet, the denser oceanic lithosphere of the nazca plate is forced down and under the more buoyant continental lithosphere of the south american plate, descending at an angle into the mantle in a process called subduction. Subduction is a geological process that takes place at convergent boundaries of tectonic plates. Subduction destructive ocean c lithosphere destroyed trench yes volcanoes volcanic arc trench. Icdp drilling in convergent and collisional plate margins faces unprecedented challenges. The nazca plate is moving eastwards, towards the south american plate, at about 79mm per year. In this book chapter, i study the alongstrike geometry of the central chilean. As the plate heats up the water is liberated, lowering the melting point of the mantle and causing partial melting. Two plates move toward each other at these destructive plate margins, where the older portions of oceanic plates are returned to the mantle.
Continents in collision modelling processes at a destructive convergent plate margin some of the earths most dramatic and damaging events take place at destructive plate margins where two continents collide. What are midoceanic ridges, subduction zones, lithospheric plates, transform faults, deep. Tectonic processes along the chile convergent margin springerlink. Oceanocean convergent plate boundaries learn that subduction of the older, denser oceanic crust leads to the formation of a volcanic island arc and accompanying earthquakes. Continental drift, sea floor spreading and plate tectonics. Midocean ridges and transform margins have shallow earthquakes usually less than 30 km deep, in narrow bands close to plate margins. Earthquakes are often accompanied by uplift of the land by as much as a few meters.
Subduction of one of the oceanic plates occurs because one plate is likely to be older and denser than the other. Continued subduction of the nazca plate brings sea water, locked in the ocean crust, deep into the mantle. An example is where the indian plate collides with the eurasian plate figure 12. Continental margins around the gulf of alaska the eastern pacific. The typical pattern of earthquakes associated with oceanocean subduction is well illustrated in the interactive figure 16 below, which shows the distribution of earthquakes associated with the tonga trench in the southwest pacific. We see the denser thinner oceanic plate diving beneath the continental plate. Andes and cascades backarc basin a basin that forms on the side of a volcanic arc away from the trench. This video describes the physical features that can be observed at three different types of convergent plate boundaries and explains the geologic processes that produce these features. The subduction zone can be defined by a plane where many earthquakes occur, called the benioff zone. Tectonic processes along the chile convergent margin.
Passive continental margins abutting the atlantic ocean and gulf of mexico developed as a large continent, pangea, ripped apart about 200 million years ago. A long, narrow and deep undersea trough is formed along the subduction zone. In this animation, we are showing an ocean continent convergent boundary. As the cold lithosphere descends into the earths interior, pressure on it increases, pushing water out of it and into the asthenosphere which cause. At one time, india was a separate continent, and ocean crust separated india from the eurasian plate. The depths of earthquakes, and the width of the band, depend on the type of plate boundary.
Subduction zones burrow deeply but are imperfectly camouflaged, and geophysics and geochemistry can be used to study them. Since the development of the theory, geologists have had to reexamine almost every aspect of. Pdf convergent plate boundries and collision zones. Convergent plate boundaries geosciences libretexts.
What is the definition of oceaniccontinental subduction. For this reason, destructive boundaries are often referred to by their alternative name of subduction zones. No subduction occurs as both plates are boyant and of low density intervening oceanic sediments trapped between two converging plates are heaved upwards, resulting in the formation of major fold mounta. In the future, as the atlantic continues to widen due to sea floor spreading in the centre, the ocean continent boundaries will eventually become subduction zones with new convergent destructive margins being formed. Cenozoic kinematics and dynamics of oblique collision between. Furthermore, the collision of hotspot tracks with a convergent margin might locally. Strong, destructive earthquakes and the rapid uplift of mountain ranges are common in these region. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes. Continental lithosphere lies at a higher surface elevation than oceanic lithosphere because of its lower overall density.
Convergent boundary in convergence there are subtypes namely. An active continental margin refers to the submerged edge of a continent overriding an oceanic lithosphere at a convergent plate boundary by opposition with a passive continental margin which is the remaining scar at the edge of a continent following continental breakup. Distinguish between convergent, divergent, and transform plate boundaries. These occur when one plate is pulled down subducted where it meets another, usually producing earthquakes and volcanic eruptions. The convergence of two plates of continental crust is known as a collision margin. The east and west sides of the atlantic are good examples at present. Globally, there are over 50 major ocean trenches covering an area of 1.
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