The diastrophism It is the geological process by which the rocks of the earth's crust are subjected to displacements, deformations, folding and fractures. This includes the rise and fall of continental masses, as well as the sinking and rising of large regions..
The main cause of diastrophism is the displacement of the earth's crust or lithosphere by the convection currents of the earth's mantle. These displacements involve continental drift and the processes of subduction of layers of the lithosphere in the mantle or asthenosphere..
Diastrophism is divided into two main types, which are epigenesis and orogenesis. Epirogenesis consists of vertical movements that affect large areas and orogenesis are horizontal movements caused by earth faults and folds..
The phenomenon of diastrophism causes the modeling of the earth's surface. As a result of epirogenic and orogenic phenomena, mountain ranges, sedimentary basins and chains of volcanic islands have emerged..
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The fundamental cause of diastrophic phenomena are the convection currents of the earth's mantle. This causes two associated processes, the displacement of the continental plates and the subduction process..
The Earth has a molten iron core at 4,000 ºC on which is a rock mantle with a predominance of silica. The rocks of the mantle are in a mixture of states, from molten, semi-molten to solid, from the lower mantle to the upper.
Below the mantle is the lithosphere or earth's crust that is in a solid state.
The difference in temperature between the bottom and the top of the mantle causes displacement of the material both horizontally and vertically. This movement is very slow on a human scale and drags the crust fragmented into large blocks (continents).
In this process, the blocks separate or collide, compressing each other and causing the different diastrophic processes. On the other hand, the mass of molten rocky material (magma) is subjected to high pressures and temperatures (600-1,000 ºC).
Because of this, magma rises through the most fragile areas of the crust and surfaces in the form of volcanic eruptions. The greatest activity occurs in the underwater mountain ranges called mid-ocean ridges..
In these ridges, the new material displaces the existing ocean floor and causes movement. That displaced ocean floor will end up colliding with the continental plates.
When an oceanic plate collides with another plate either oceanic or a higher continental one, the oceanic floor is forced to sink. This phenomenon is known as subduction and pushes the oceanic crust towards the mantle, melting there due to high temperatures..
The entire system behaves like a conveyor chain that produces new crust on the one hand (volcanism) and recycles it on the other (subduction). At the points where subduction occurs, strong upward and downward pressures are generated, as well as horizontal displacements..
There are two main types of diastrophism, defined according to their amplitude and intensity, these are epirogenesis and orogenesis..
Epirogenesis deals with processes of a vertical nature, of slow ascents and descents, which affect large areas of land. However, its effect on the arrangement of materials is not very marked, producing what is called calm structures..
These ascending and descending movements generate structures that can be monoclinal or aclinear. In the first case, they are geological structures where all the layers are parallel to each other and with the slope in only one direction..
Whereas the aclinear are bulges without any folding and can be positive, forming hills or negative and forming basins of accumulation.
Shields are formed by epigenesis, such as the Guiana Shield (northern South America) or the Canadian Shield, with Precambrian outcrops. These diastrophic processes also give rise to sedimentary basins.
Here reference is made to the subsidence of the earth's crust, which even if they are a few hundred meters long, cause significant effects. For example, subsidence of the continental shelf has caused the intrusion of the sea into the interior of the continents.
It is about the upward movements of the earth's crust that in the same way, although slow and without great elevations, cause significant changes. For example, the elevation of the continental ground level has caused the withdrawal of shallow marine waters that occupied continental areas..
For its part, orogenesis refers to horizontal processes that affect narrow areas of the earth's crust. In this case, its effect on the arrangement of materials is very marked and tormented structures are generated that cause displacements..
This is because orogenic processes occur at the connection points of the continental plates. The plates, as they move against each other, produce large compression tangential forces.
Therefore, folds, fractures, deformations and displacements are generated that originate faulted and folded reliefs..
Geological faults are plane fractures where the two resulting blocks move vertically or horizontally relative to each other. They are originated by horizontal pressures due to the displacement of the continental masses and when they are active they generate earthquakes.
There are different types of failures depending on the direction of the pressure, and they can be normal or reverse tearing failures. In the first case the blocks are separated from each other, while in the second the blocks are compressed one to another.
On the other hand, in tearing or transformation faults, the blocks move horizontally with respect to each other..
This is a very particular type of reverse fault, in which the rocks of the lower strata are pushed upwards. This means that the oldest geological materials are above the most recent, that is, they ride.
Folds generally occur in sedimentary rocks subjected to horizontal pressures. Faced with these pressures, the rock strata do not break, they only fold or curve forming undulations..
When the fold is convex, forming a ridge, it is called anticline, while if it is concave, forming a valley, it is called syncline..
Diastrophism is one of the causes of the formation of the reliefs of the planet, islands, mountain ranges, sedimentation basins, among other physiographic features..
In the limits between oceanic plates, when subduction of one under the other occurs, faults and uplift movements occur. This creates underwater ridges with volcanic activity, outcropping some elevations and forming volcanic island chains..
These are the so-called volcanic island arches that abound in the western Pacific Ocean and are also found in the Atlantic. For example, the Aleutian Islands in the Pacific and the Lesser Antilles in the Caribbean Sea (Atlantic).
Mountain ranges are created in large areas of contact between continental plates or between an oceanic plate and a continental one. An example is the Andes mountain range formed by the collision of an oceanic plate (of the Pacific) against a continental one (South American plate).
In the case of the Himalayas mountain range, it originated from the collision of two continental plates. Here, the Indian plate derived from the ancient continent Gondwana and the Eurasian plate impacted 45 million years ago..
For its part, the Appalachian Mountains were formed by the collision of the continental plates of North America, Eurasia and Africa, when they formed the Pangea continent..
The processes of positive epyrogenesis have caused the outcrop of extensive areas of metamorphic and igneous Precambrian rocks. Forming mostly flat landscapes or with hills and plateaus, but also elevated areas.
In America there are shields in Canada and in South America and Greenland it is made up of a large shield. In Eurasia there are shields to the north in the Baltic and in Siberia and to the south in China and India.
Later, they occupy large areas in Africa and the Arabian Peninsula. Finally, they also appear in Australia, especially in the West.
Due to epirogenic movements of descent of the continental shelf on the north coast of South America during the Paleozoic, marine penetration occurred. This originated a shallow sea that covered part of the extension of what is currently Venezuela..
Later, the ascent movements made the sea recede, the sediments were compacted, and later in the tertiary period they were elevated in the Andean orogenesis. Today Ammonite fossils are found from that ancient shallow sea at more than 3,000 meters above sea level in the Andes..
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