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Comment se forme un nouvel océan ? © peangdao, Adobe Stock

How is a new environment born?

On Earth, there is no ocean that is more than 200 million years old, which testifies to the great periodicity of tectonic processes. Very regularly, some oceans close while others open. But how is the birth of a new ocean?

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if it was a movement Tectonic plates can cause major continental collisions and generate mountain ranges such as the Alps or the Himalayas, and they are also closely linked to another major phenomenon in the tectonic cycle: the opening of new oceans.

Over the course of geological time, the Earth has in fact experienced several major tectonic cycles that led to the formation of Super Continents. During these stages where everything masses The continents are grouped together, and one ocean occupies the majority of the Earth’s surface. Deep operations but also limitations related to the continuous creation of oceanic crust and his Recycling at the level of regions subduction It means that this configuration cannot remain static. After the reassembly stage, there inevitably follows a stageContinental Opening. These different stages are part of Wilson cycle.

Continental rifting and rupture: the previous stages of the ocean opening

However, a continent that separates (completely) into two spontaneously gives birth to a new ocean. This is the new method, after the stage of the continental extension ocean edge. For example, the Mid-Atlantic mountain range was born as a result of a turbulence The supercontinent Pangea. 180 million years ago, the plates of South America and Africa began to separate. will follow them Separation Plates of North America and Eurasia.

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thinning and breaking continental crust It is part of the cracking process. The creation of a new oceanic ridge will occur only at the end of this rupture process, the mechanisms of which can be varied and take more or less time, particularly depending on the Speed To stretch the plates no more than a few centimeters per year. The mechanism leading to the formation of a new ocean thus extends over tens of millions of years.

Local elevation of the auricle

Oceanic ridges are defined by a highly localized elevation Coat Warm moor. this ascent peridot At more than 1300 ° C accompanied by a process partial fusion who is born the silhouette Morp type. By crystallizing at different depths, this magma will produce new crust, whose composition is significantly different from that of the continental crust. This is the oceanic crust. Talking about the ocean When a ridge enters the activity and produces an oceanic crust.

But how is the ridge formed?

It’s all about stretching and equal balance. continental crust It has a lower density than the mantle, it “floats” on top of this denser medium. But when thinned, this difference in thickness will cause a deep material flow, with the goal of “compensating” for this loss of thickness. Therefore, the fault zones are characterized by the elevation of the Mori mantle layer below the zone of greatest thinning. This is also why Alsace, an ancient incomplete rift, is so strong regression Geothermal energy that allows in particular Exploiting the basement heat.

As the continental crust gradually declines, and with it all of the continental lithosphere (which includes the upper mantle),Acinosphere It rises and can begin to produce magma if thermal conditions permit. This is how continental edges of magma or poor magma are obtained, depending on the ability of the system to extract magma from the mantle at this point.

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Some ocean births take longer than others

When the continental extension reaches a critical point, the continental crust, which is weakening to the maximum, will have no choice but to break. The story may end there in some cases at the coat lithosphere It was weak at the same time, if not before, the continental crust. Then the asthenosphere is high enough to generate a large pot Sizes from magma. In this case, the rupture of the crust is accompanied by the creation of a stable magmatic system and thus the initiation of a ridge and the creation of a new ocean, between the two recently separated continental masses.

In other cases, We still have to wait Before seeing the real ridge begins. In fact, if the continental lithosphere was very cold (and therefore very dense), it would not be fracturing at the same time as the crust. Then, the rise in the asthenosphere is not high enough to initiate active and stable molten action immediately. The extension will continue to absorb itself by exposing undissolved mantle rock from the rest of the subcontinental mantle, until it is exhausted. In this type of formation, the creation of an oceanic ridge is delayed and the final rupture of the subcontinental mantle will follow. Delivery, in this case, is a little longer!

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