plate tectonics | Definition, Theory, Facts, & Evidence | yogada.info
How is Mantle Convection Related to Plate Tectonics? continents, and mountains, it is also the ultimate reason for nearly all earthquakes and volcanoes . Convergent boundaries -- where crust is destroyed as one plate dives under another. which extends from the Arctic Ocean to beyond the southern tip of The volcanic country of Iceland, which straddles the Mid-Atlantic. A string of volcanoes stretches from the southern tip of South A convergent plate boundary is formed by tectonic plates crashing into.
Instead of being subducted, these slices are thrust over the overriding plate and are said to be obducted. Where this occurs, rare slices of ocean crust, known as ophiolitesare preserved on land. They provide a valuable natural laboratory for studying the composition and character of the oceanic crust and the mechanisms of their emplacement and preservation on land. A classic example is the Coast Range ophiolite of Californiawhich is one of the most extensive ophiolite terranes in North America.
These ophiolite deposits run from the Klamath Mountains in northern California southward to the Diablo Range in central California. This oceanic crust likely formed during the middle of the Jurassic Periodroughly million years ago, in an extensional regime within either a back-arc or a forearc basin.
In the late Mesozoicit was accreted to the western North American continental margin. Because preservation of oceanic crust is rare, the recognition of ophiolite complexes is very important in tectonic analyses. Until the mids, ophiolites were thought to represent vestiges of the main oceanic tract, but geochemical analyses have clearly indicated that most ophiolites form near volcanic arcs, such as in back-arc basins characterized by subduction roll-back the collapse of the subducting plate that causes the extension of the overlying plate.
The recognition of ophiolite complexes is very important in tectonic analysis, because they provide insights into the generation of magmatism in oceanic domains, as well as their complex relationships with subduction processes. See above back-arc basins. Mountains by continental collision Continental collision involves the forced convergence of two buoyant plate margins that results in neither continent being subducted to any appreciable extent.
A complex sequence of events ensues that compels one continent to override the other. The subducted slab still has a tendency to sink and may become detached and founder submerge into the mantle. The crustal root undergoes metamorphic reactions that result in a significant increase in density and may cause the root to also founder into the mantle. Both processes result in a significant injection of heat from the compensatory upwelling of asthenosphere, which is an important contribution to the rise of the mountains.
Continental collisions produce lofty landlocked mountain ranges such as the Himalayas.
Much later, after these ranges have been largely leveled by erosionit is possible that the original contact, or suture, may be exposed. The balance between creation and destruction on a global scale is demonstrated by the expansion of the Atlantic Ocean by seafloor spreading over the past million years, compensated by the contraction of the Pacific Oceanand the consumption of an entire ocean between India and Asia the Tethys Sea.
The northward migration of India led to collision with Asia some 40 million years ago. Since that time India has advanced a further 2, km 1, miles beneath Asia, pushing up the Himalayas and forming the Plateau of Tibet. Pinned against stable SiberiaChina and Indochina were pushed sideways, resulting in strong seismic activity thousands of kilometres from the site of the continental collision.
Transform faults are so named because they are linked to other types of plate boundaries. The majority of transform faults link the offset segments of oceanic ridges.
However, transform faults also occur between plate margins with continental crust—for example, the San Andreas Fault in California and the North Anatolian fault system in Turkey. These boundaries are conservative because plate interaction occurs without creating or destroying crust.
Because the only motion along these faults is the sliding of plates past each other, the horizontal direction along the fault surface must parallel the direction of plate motion.
The fault surfaces are rarely smooth, and pressure may build up when the plates on either side temporarily lock. This buildup of stress may be suddenly released in the form of an earthquake. Geological Survey Many transform faults in the Atlantic Ocean are the continuation of major faults in adjacent continents, which suggests that the orientation of these faults might be inherited from preexisting weaknesses in continental crust during the earliest stages of the development of oceanic crust.
On the other hand, transform faults may themselves be reactivated, and recent geodynamic models suggest that they are favourable environments for the initiation of subduction zones. Linear chains of islandsthousands of kilometres in length, that occur far from plate boundaries are the most notable examples. These island chains record a typical sequence of decreasing elevation along the chain, from volcanic island to fringing reef to atoll and finally to submerged seamount.
An active volcano usually exists at one end of an island chain, with progressively older extinct volcanoes occurring along the rest of the chain. Tuzo Wilson and American geophysicist W. Jason Morgan explained such topographic features as the result of hotspots.
Volcanoes and their relation to plate tectonics
The principal tectonic plates that make up Earth's lithosphere. Also located are several dozen hot spots where plumes of hot mantle material are upwelling beneath the plates. Black dots indicate active volcanoes, whereas open dots indicate inactive ones. The number of these hotspots is uncertain estimates range from 20 tobut most occur within a plate rather than at a plate boundary. Hotspots are thought to be the surface expression of giant plumes of heat, termed mantle plumesthat ascend from deep within the mantle, possibly from the core-mantle boundary, some 2, km 1, miles below the surface.
Relationship Between Volcanoes & Plate Boundaries by Shelby Soto on Prezi
These plumes are thought to be stationary relative to the lithospheric plates that move over them. A volcano builds upon the surface of a plate directly above the plume. As the plate moves on, however, the volcano is separated from its underlying magma source and becomes extinct. Extinct volcanoes are eroded as they cool and subside to form fringing reefs and atollsand eventually they sink below the surface of the sea to form a seamount. At the same time, a new active volcano forms directly above the mantle plume.
Diagram depicting the process of atoll formation. Atolls are formed from the remnant parts of sinking volcanic islands. The best example of this process is preserved in the Hawaiian-Emperor seamount chain. The plume is presently situated beneath Hawaii, and a linear chain of islandsatollsand seamounts extends 3, km 2, miles northwest to Midway and a further 2, km 1, miles north-northwest to the Aleutian Trench.
The age at which volcanism became extinct along this chain gets progressively older with increasing distance from Hawaii —critical evidence that supports this theory. Hotspot volcanism is not restricted to the ocean basins ; it also occurs within continents, as in the case of Yellowstone National Park in western North America.
Measurements suggest that hotspots may move relative to one another, a situation not predicted by the classical model, which describes the movement of lithospheric plates over stationary mantle plumes.
This has led to challenges to this classic model. Furthermore, the relationship between hotspots and plumes is hotly debated. Proponents of the classical model maintain that these discrepancies are due to the effects of mantle circulation as the plumes ascend, a process called the mantle wind.
Data from alternative models suggest that many plumes are not deep-rooted. Instead, they provide evidence that many mantle plumes occur as linear chains that inject magma into fractures, result from relatively shallow processes such as the localized presence of water-rich mantle, stem from the insulating properties of continental crust which leads to the buildup of trapped mantle heat and decompression of the crustor are due to instabilities in the interface between continental and oceanic crust.
In addition, some geologists note that many geologic processes that others attribute to the behaviour of mantle plumes may be explained by other forces. The point of emergence of the axis through the surface of the sphere is known as the pole of rotation. Therefore, the relative motion of two rigid plates may be described as rotations around a common axis, known as the axis of spreading. Application of the theorem requires that the plates not be internally deformed—a requirement not absolutely adhered to but one that appears to be a reasonable approximation of what actually happens.
Application of this theorem permits the mathematical reconstruction of past plate configurations. Theoretical depiction of the movement of tectonic plates across Earth's surface. Movement on a sphere of two plates, A and B, can be described as a rotation around a common pole. Circles around that pole correspond to the orientation of transform faults that is, single lines in the horizontal that connect to divergent plate boundaries, marked by double lines, in the vertical.
Because all plates form a closed system, all movements can be defined by dealing with them two at a time. The joint pole of rotation of two plates can be determined from their transform boundaries, which are by definition parallel to the direction of motion.
Thus, the plates move along transform faultswhose trace defines circles of latitude perpendicular to the axis of spreading, and so form small circles around the pole of rotation.
A geometric necessity of this theorem—that lines perpendicular to the transform faults converge on the pole of rotation—is confirmed by measurements. This relationship is also confirmed by accurate measurements of seafloor-spreading rates.
To determine the true geographic positions of the plates in the past, investigators have to define their motions, not only relative to each other but also relative to this independent frame of reference. Hotspotsas classically interpreted, provide an example of such a reference frame, assuming they are the sources of plumes that originate within the deep mantle and have relatively fixed positions over time.
If this assumption is valid, the motion of the lithosphere above these plumes can be deduced. Based on observations of the rates at which the surface of Earth moves, geologists estimate the mantle convectively flows at rates of several centimeters a year. The heat driving mantle convection has three sources. Mantle convection is the main mechanism by which this heat escapes from the interior of Earth. Plate tectonics refers to the movement of the rigid plates around the surface of Earth.
The outer portion of the planet, or lithosphere, is relatively rigid because it is relatively cold. The lithosphere varies in thickness but is typically a hundred or so kilometers thick. It includes the upper mantle and both the continental and oceanic crust. These plates may move away from, move by, or collide with each other.
This process forms ocean basins, shifts continents, and pushes up mountains. Tectonic plates break apart and diverge where the mantle beneath is upwelling. In such regions mid-ocean ridges develop, and new lithosphere and crust form to replace the material that is moving away. Where plates converge, usually where the mantle is downwelling, one plate is forced beneath another.
When this involves plates with embedded continental crust, mountain belts such as the Alps and Himalayas form. Shasta Siskiyou County and Red Hill Imperial County A volcano is an opening in the earth's crust that allows molten rock from the mantle to flow out onto the surface as lava. Volcanoes also emit vast amounts of gas, primarily carbon dioxide, water vapor and sulfur dioxide. The fine solid rock particles injected into the atmosphere by an eruption can remain aloft for years.
Volcanoes are associated with three types of tectonic structures: California has all three. The SAF is a transform plate boundary strike slip fault and so is not accompanied by volcanic activity. The eruption of Mount St. Helens was a vivid reminder that the continental US has active volcanoes, of them.
The Salton Domes are five small inactive rhyolitic volcanoes.