Convergent Boundaries
Continental-continental divergent/constructive boundary In, 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 that are moving away from each other. Divergent boundaries within initially produce which eventually become. Most active divergent plate boundaries occur between and exist as. Divergent boundaries also form which occur when the plates move apart to produce gaps which molten lava rises to fill. Current research indicates that complex within the 's allows material to rise to the base of the beneath each divergent plate boundary. This supplies the area with vast amounts of heat and a reduction in pressure that melts from the (or upper mantle) beneath the rift area forming large or lava flows.
Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other. Over millions of years, tectonic plates may move many hundreds of kilometers away from both sides of a divergent plate boundary.
Because of this, rocks closest to a boundary are younger than rocks further away on the same plate. Bridge across the in southwest, that is part of the boundary between the Eurasian and North American continental tectonic plates. At divergent boundaries, two plates move away from each other and the space that this creates is filled with new crustal material sourced from molten that forms below.
The origin of new divergent boundaries at is sometimes thought to be associated with the phenomenon known as. Here, exceedingly large convective cells bring very large quantities of hot asthenospheric material near the surface and the is thought to be sufficient to break apart the lithosphere. The hot spot which may have initiated the Mid-Atlantic Ridge system currently underlies Iceland which is widening at a rate of a few centimeters per year.
Divergent boundaries are typified in the oceanic lithosphere by the rifts of the oceanic ridge system, including the Mid-Atlantic Ridge and the, and in the continental lithosphere by rift valleys such as the famous East African. Divergent boundaries can create massive fault zones in the oceanic ridge system. Spreading is generally not uniform, so where spreading rates of adjacent ridge blocks are different, massive transform faults occur. These are the, many bearing names, that are a major source of.
A sea floor map will show a rather strange pattern of blocky structures that are separated by perpendicular to the ridge axis. If one views the sea floor between the fracture zones as conveyor belts carrying the ridge on each side of the rift away from the spreading center the action becomes clear. Crest depths of the old ridges, parallel to the current spreading center, will be older and deeper. (from thermal contraction and ).
It is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of the seafloor spreading hypothesis was found. Airborne surveys showed a strange pattern of symmetrical on opposite sides of ridge centers.
The pattern was far too regular to be coincidental as the widths of the opposing bands were too closely matched. Scientists had been studying and the link was made by, and in the. The magnetic banding directly corresponds with the Earth's polar reversals. This was confirmed by measuring the ages of the rocks within each band. The banding furnishes a map in time and space of both spreading rate and polar reversals.
Convergent Boundaries Volcanoes
Examples. Other plate boundary types.
See also. – A process at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. – The movement of the Earth's continents relative to each other. – A geological process at convergent tectonic plate boundaries where one plate moves under the other References.
Convergent Boundary Where a convergent boundary forms A convergent boundary forms when two continental plates collide. Neither plate subducts because the crusts have approximately the same density. Instead, the rocks are smashed together causing them to recrystallize due to the intense heat and pressure from the colliding plates. Formation of great mountain chains The rocks as they are compressed begin forming mountains above the Earth's surface.
The continental crust increases in depth as the mountains grow above. The thickest crust on our planet lies beneath mountain chains formed when two continental crusts have converged. Himalaya Mountains are convergent boundary Formation convergent boundaries A tectonic plate boundary always forms when two continental plates collide. Neither plate subducts because the crust have approximately the same density.
Instead, the rocks are smashed together causing them to recrystallize due to the intense heat and pressure from the colliding plates. The rocks as they are compressed begin forming mountains above the Earth's surface. The continental crust increases in depth as the mountains grow above.
The thickest crust on our planet lies beneath mountain chains formed when two continental crusts have formed a convergent boundary. Subduction zones Subduction zones form when an oceanic plate collides with another oceanic plate or continental plate. The continental crust is lighter and less dense than oceanic crust. Continental crust's density is approximately 2.7 grams per cubic centimeter. Oceanic crust is thinner and the average density is about 3.3 cubic centimeters.
When the two crustal plates converge the oceanic plate always bends and subducts beneath a continental plate. Subduction zones that occur on the coastline of Alaska are areas of frequent large and small earthquakes. The plates lock and break apart creating these earthquakes which occasionally send tsunami waves traveling across the Pacific Ocean to distant shores. Ocean crusts collide When two oceanic plates meet the older and colder plate like the Pacific Ocean Plate is heavier and denser. The leading edge of the plate bends and slips beneath the younger oceanic plate. Off the island of Guam is the Mariana Trench the deepest area on our planet.
In this area the leading edge of the Pacific Plate is forced beneath the smaller and lighter Mariana Plate. The trench that has formed between the two plates includes the Challenger Deep. Collision boundary land forms Each of these boundaries are associated with specific land forms.
Collision boundaries form great mountain chains on Earth. The European Alps and the are examples of the land forms visible on Earth where continental crusts came together. Great volcanic mountains like Mount Rainier form in a subduction zone on the continental side of a subduction zone. The Aleutian Islands in the North Pacific are an example of a volcanic island arc that has formed above a subduction zone. More Facts About Earth Links.