DIASTROPHISM: CAUSES, TYPES, CONSEQUENCES - ENVIRONMENT - 2025

The diastrophism is the geological process by which rocks of the crust are subjected to displacements, strains, folds 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.

Folding in sedimentary rocks. Source:

Diastrophism is divided into two main types, which are epi-genesis 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 the epirogenic and orogenic phenomena, the mountain ranges, the sedimentary basins and the volcanic island chains have emerged.

Causes

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.

- Continental drift

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 one.

Below the mantle is the lithosphere or earth's crust that is in a solid state.

Convection currents

The difference in temperature between the bottom and the top of the mantle causes both horizontal and vertical displacement of the material. 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 emerges 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.

- Subduction

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 it pushes the oceanic crust towards the mantle, melting there due to the high temperatures.

Tectonic plates. Source: English: Translated by Mario Fuente Cid in Inkscape Free Software Spanish: Translated by Mario Fuente Cid in Inkscape Free Software

The whole system behaves like a conveyor chain that on the one hand produces new crust (volcanism) and on the other recycles it (subduction). At the points where subduction occurs, strong upward and downward pressures are generated, as well as horizontal displacements.

Types

There are two main types of diastrophism, defined according to their amplitude and intensity, these are epirogenesis and orogenesis.

- Epigenesis

Epirogenesis deals with the 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.

Monocline and aclinear

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.

While the aclinear are bulges without any folding and can be positive, forming hills or negative and forming basins of accumulation.

Guiana Shield in Venezuela. Source:

By epigenesis, shields are formed, such as the Guiana Shield (northern South America) or the Canadian Shield, with Precambrian outcrops. These diastrophic processes also give rise to sedimentary basins.

Negative epirogenic movements

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.

Positive epirogenic movements

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.

- Orogenesis

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, in their movement against each other, produce large tangential compression forces.

Therefore, folds, fractures, deformations and displacements are generated that cause faulted and bent reliefs.

Faults

Geological faults are plane fractures where the two resulting blocks move vertically or horizontally with respect to each other. They are caused by horizontal pressures due to the displacement of the continental masses and when they are active they generate earthquakes.

San Andrés fault (United States). Source: Ikluft

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.

Thrust

This is a very particular type of reverse fault, in which the rocks of the lower strata are pushed upwards. This causes that the oldest geological materials are above the most recent, that is, they ride them.

Folds

Folds generally occur in sedimentary rocks subjected to horizontal pressure. Faced with these pressures, the rock strata do not break, they only fold or curve forming undulations.

When the fold is convex, forming a crest, it is called anticline, while if it is concave, forming a valley, it is called synclinal.

Consequences

Diastrophism is one of the causes of the formation of the reliefs of the planet, islands, mountain ranges, sedimentation basins, among other physiographic features.

Volcanic islands

In the limits between oceanic plates, when subduction of one under the other occurs, faults and uplift movements occur. This creates submarine ridges with volcanic activity, outcropping some elevations and forming volcanic island chains.

Easter Island (Volcanic). Source: Alanbritom

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

In large areas of contact between continental plates or between an oceanic plate and a continental they create mountain ranges. 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).

Himalayas mountain range. Source: Guilhem Vellut from Paris

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 Gondwana continent 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.

Shields

The processes of positive epyrogenesis have caused the outcrop of extensive areas of precambrian metamorphic and igneous 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.

Shallow seas

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 now Venezuela.

Subsequently, the ascent movements made the sea recede, the sediments were compacted, and later in the tertiary they were raised 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.

References

1. Billings, MP (1960). Diastrophism and mountain building. Geological Society of America Bulletin.
2. Chamberlin, RT (1925). The Wedge Theory of Diastrophism. The Journal of Geology.
3. Rojas-Vilches, OE (2006). Diastrophism. Epirogenesis and orogenesis. University of Concepción, Faculty of Architecture-Urbanism-Geography.
4. Scheidegger, AE (1952). Physical aspects of the contraction hypothesis of orogenesis. Canadian Journal of Physics.
5. Sudiro, P. (2014). The Earth expansion theory and its transition from scientific hypothesis to pseudoscientific belief. Hist. Geo Space Sci.