How do the tectonic forces that move continents work ?

© Qingbao Meng/Unsplash

Our beautiful planet Earth is constantly changing. Continents move, mountains form, trenches are dug at the bottom of the oceans, volcanoes rumble and earthquakes shake its surface. These phenomena, most of which are invisible to the naked eye, are the result of tectonic forces that act in the depths of the Earth. These are a dynamic and continuous process, sculpting our planet for billions of years. What are the cogs of this natural mechanism ?

Tectonic forces: a complex mechanism

The theory of plate tectonics, a fundamental paradigm elucidating the dynamics of the earth's crust, gained the support of the geological community during the 1960s. This model is based on the postulate that the lithosphere, rigid outer layer of our planet encompassing the crust and the upper part of the mantle, consists of several moving plates sliding on the asthenosphere, a more malleable layer of the upper mantle.

These tectonic plates, amalgamating oceanic and continental lithosphere, are in perpetual movement, a phenomenon made possible by the convection currents which animate the earth's mantle. At the incandescent heart of our planet, the intense heat causes the burning magma to rise towards the surface, while the cooled magma sinks, thus generating these convective currents which drag the tectonic plates as they drift on the asthenosphere.

There are three main types of plate movements. First, the divergence zones, where two plates move away from each other, allowing magma to rise and to form new oceanic crusts, giving rise to mid-ocean ridges (seamounts). Secondly, the convergence zones, theater of the meeting between plates, where one sinks under the other in a subduction process, leading to the partial melting of rocks, volcanic activity and the formation of mountain ranges. Finally, the transformation zones, where two plates slide horizontally against each other, sometimes causing violent earthquakes.< /p>

These complex interactions between plates are at the origin of numerous geological phenomena. Earthquakes result from sudden movements along faults, while volcanoes emerge mainly in subduction zones and ocean ridges. The imposing mountain ranges, such as the Himalayas, the Alps, the Caucasus or the Andes are the result of the titanic collision between continental plates.

The Continental drift caused by these plate movements also causes continuous modification and movement of the continents. As you can see in the video below, in 250 million years, the Earth as we know it will no longer exist, and the emerged parts would theoretically only form: a super-continent: the next Pangea.

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The scientific debate: cause or consequence?

Geologists have wondered at length about the genesis of the driving forces of tectonic plates. The question was to determine if the convective movements of the Earth's mantle were at the origin of the movement of the plates or if, conversely, the migration of the plates on the surface dragged the mantle. This problem is & #8217;related to the famous chicken and egg paradox.

To elucidate this mystery, a team of Researchers took a holistic approach, viewing the Earth as an indivisible system. They developed a model of the evolution of a fictional planet, similar to ours. Their study, published in 2019 in Science Advances, required nine months of intensive calculations on a supercomputer to simulate 1.5 billion years of geological evolution.

The results of this modeling revealed that two-thirds of the Earth's surface is moving faster than the underlying mantle, suggesting a pull exerted by the surface on the Earth's depths. However, this dynamic of forces fluctuates according to the geological eras. Thus, during the formation of supercontinents, continental movements are mainly induced by deep mantle currents. Conversely, during the fragmentation of these supercontinents, it is the plunging plates which dictate the movements observed.

So the egg or the hen ? Well, actually, a bit of both. The results of this study clearly prove that the interactions between the Earth's surface and the mantle are complex and bidirectional. The surface and the mantle influence each other, depending on the geological periods and tectonic configurations at time T.

• Tectonic plates move thanks to convection currents in the Earth's mantle.
• The movements of these plates cause the continents to drift and cause numerous phenomena geological.
• The relationship between the mantle and the plates is complex and bidirectional, mutually influencing their movement over time.

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