Plate Boundaries - Geology for Kids
There are three different kinds of movement at plate boundaries! . When an oceanic plate meets a continental or another oceanic plate, subduction occurs. Because they are both continental crust, they have the same density, so when they FORMS WHERE 1 CONTINENTAL AND 1 OCEANIC PLATE are MOVING . These plates are one of two primary types: oceanic plates or continental plates. While these two types of plates share a lot in common, there are.
The main features are indicated in the diagram below.
The swell is seen by a bulge in the in the downgoing plate where it is subducted into the mantle. The backarc region is located behind the arc and can be compressed or extended.
Ocean-ocean collision zone Ocean-Continent Collisions When an oceanic and a continental plate collide, eventually the oceanic plate is subducted under the continental plate due to the high density of the oceanic plate. Once again a benioff zone forms where there are shallow intermediate and deep focus earthquakes.
Difference Between Continental & Oceanic Plates | Sciencing
As the oceanic plate is subducted sediment is scraped off to form an acretionary wedge at the point of collision between the two plates. When the oceanic plate is subducted due to partial melting of the asthenosphere magma with an andesitic composition is formed.
The magma formed is less dense than the surrounding material so it rises to the surface to form a magmatic arc on the edge of the continent which the oceanic plate is subducted under. Over time the continental margin, due to compression forms into a folded mountain belt.
As time goes on the hot magma rising upward from the subduction zone causes further compression of the mountain belt. Deep mountain roots form and are gradually metamorphosed and intruded with granitic plutons. Pertinent features of the continental crust are: It consists overall of material with granitic composition granites and gneisses of granitic composition, other compositional rock types, such as basalts are present, but volumetrically not important From the travelling velocity of seismic waves in the continental crust we know that the lower portions of the continental crust are denser than the upper portions, probably because of a downwards increase of rocks of more basaltic composition Continental crust is thickest beneath mountain ranges root zones, kmelsewhere the thickness is about 30 km.
The structure of the continental crust is considerably more complex than the simple layer structure of the oceanic crust.
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- Ocean-Continent Collisions
It consists of intensely deformed metamorphic rocks derived from sediments and volcanic rocks that are intruded by granites, and may have been partially remolten to granites. The oldest continental crust has been determined to be about 3. They cover nowadays about one third of the earth's surface, but initially the proportion of the oceans may have been much larger. The continental crust is the end product of planetary differentiation accumulation of light materialsand within the crust of each continent we can distinguish three basic components: SHIELDS contain the bulk of the rock record of continental evolution and growth, and are thus the key to the understanding of the origin of continents.
As noted earlier, they are essentially flat and consist of a complex arrangement of igneous and metamorphic rocks. The mere fact that these rocks are exposed at the surface now, implies that many kilometers of rock were eroded from the continent before these rocks finally came to the surface.
What Happens Where Tectonic Plates Meet?
If the shield rocks of a continent are studied with respect to their metamorphic age, it often turns out that those on the center are the oldest ones, and that there are several belts of metamorphic rocks that get progressively younger outward. The oldest portions of the shields consist of a mixture of volcanic rocks basalts, andesites and volcanic derived sediments erosion of volcanoesand the rocks show similarity to the material accumulating in modern day island arcs.
We know now that his shortening is a direct reflection of the compressive stress regime and subduction of oceanic crust along convergent plate margins, but before plate tectonics the missing crust was very troublesome thing to explain. The location of these fold belts along continental margins implies that by convergence of plates material is piled up along the continents, and finally becomes part of the continental crust.
Fold belts that are terminated abruptly at the continental margin, such as the Appalachians and the Caledonides, suggest that he fold belts were once much longer, and have been separated when continents broke up by continental rifting. From Mountain Belt to Continent When a mountain belt is formed along a continental margin by subduction, sedimentary and volcanic rocks are buried deeply and undergo high-pressure and high-temperature metamorphism in the root zone of the mountain belt.
Also, parts of the buried material as well as of the subducted oceanic plate melt, and granitic and andesitic magmas rise.
Ocean-Continent Convergent Plate Boundaries ( Read ) | Earth Science | CK Foundation
A considerable portion of the granites never rises to the upper portions of the mountain range, and crystallizes within the realm of the metamorphic rocks in the lower portions. This process continues until the fold belt is eroded down to sealevel, then erosion stops and isostatic uplift ceases D.
By that time the outcropping rocks will be the high grade metamorphics and granites of the root zone. We started with a folded mountain belt, and through continued erosion we have produced a new piece of shield material.
Formation of a fold belt and a metamorphosed root zone on convergent plate boundaries is also known as orogeny or creation of mountain ranges. Initially A we might for example have only oceanic crust, convergence of oceanic plates and formation of island arc complexes andesitic material, too light to be again subducted.
We start accreting material folded mountain belts to the initial arc, an embryonic continent is formed C. The continent is eroded and quartz, feldspar, and clay-rich sediments accumulate around its margins.
Renewed subduction pushes up new folded mountain belts, accompanied by metamorphism and granite plutonism. Finally the new fold belt is worn down and another segment has been added to the growing continent D.
Crustal recycling and the differentiation of the continental crust is intimately related to the composition of the oceans, the supply of nutrients for the global biomass, and thus is also linked to those global feedback mechanisms that we consider essential for climate regulation carbon cycle etc.
In part, the biosphere has adapted opportunistically to whatever chemical components were provided in the process, but it also has an active role through the weathering of continents, the deposition of carbonate banks, the carbon cycle feedbacks with climate, etc. I hope that in the course of this lecture you have gained insights into three topical complexes: Simply through evolutionary selection pressures it may have evolved to participate in climate regulation for most of Earth history.
Eventually, all things merge into one, and a river runs through it. The river was cut by the world's great flood and runs over rocks from the basement of time. On some of the rocks are timeless raindrops. Under the rocks are the words, and some of the words are theirs. I am haunted by waters. This difference in relative density causes oceanic plates to subduct beneath the more buoyant continental plates. This also allows the denser oceanic plates to sink further into the fluid asthenosphere, causing them to lie below sea level.
In contrast, the more buoyant continental plates float higher, resulting in dry land. Differences in Age Oceanic and continental plates differ radically in age because of tectonic processes.
Divergent plate boundaries continually renew oceanic plates while the subduction zones of convergent boundaries continually recycle them. As a result, the oldest oceanic rocks are less than million years old. In contrast, continental plates take a long time to form but are rarely destroyed. Much of the continental crust exceeds 1 billion years in age, and its oldest rocks may be as old as 4 billion years.