The earth's crust drips "like honey" under the Andes

The earth’s crust drips “like honey” under the Andes

This discovery documented in a new study by researchers at the University of Toronto actually describes a phenomenon at work…for several million years.

In a new study published Tuesday, June 28, 2022, in the journal Earth and Environment Communications, a team of researchers led by Julia AndersonPhD student in Earth Sciences at the University of Toronto (Canada), announce that they have made an important geological discovery.

By implementing a relatively simple model and comparing the results obtained with real data, the scientists were able to gather convincing evidence that the earth’s crust drips “like honey” for hundreds of kilometers under the mountainous massif of the Andes mountain range, which extends from the southernmost point of Argentina to the north of Colombia.

But rest assured: this phenomenon, known as d’lithospheric driphe’s actually at work for millions of yearsand this in various regions of the globe, for example in the heart of the Anatolian plateau, in central Turkey, or even on the side of the Great Basin of the United States, a desert region of the American West.

What is lithospheric dripping?

To understand this phenomenon, let us first recall that the outer regions of the Earth’s geology break down into two main parts, a crust and an upper mantle that form rigid plates of solid rock, the lithosphere, and on the other hand the hotter and more pressurized rocks. from the lower mantle.

Lithospheric (or tectonic) plates float in this lower mantle, and their magmatic convection currents can pull the plates apart to form oceans, rub against each other to trigger earthquakes, or cause them to slide under one another to form mountains.

Now, lithospheric dripping occurs when two lithospheric plates collide and heat up to such an extent that they thicken, creating a heavy “droplet” that drips into the lower part of the planet’s mantle. And as this massive droplet insinuates itself into the lower layers of our planet, it tugs at the crust above it, forming a basin on the surface.

Finally, when his weight becomes too great, his lifeline breaks and the crust above springs upward, resulting in the formation of mountain ranges. In this case, researchers have long suspected that such a phenomenon is at the origin of the formation of the Andes.

Subduction and lithospheric dripping, two related phenomena?

The Andes massif comprises in particular the Altiplano-Puna plateau, an area of ​​about 1,800 km that spills over the borders of several countries (Peru, Bolivia, Argentina and Chile). The latter was most likely created by subduction, the name given to the process of sinking a tectonic plate under another plate of lower density.

But this phenomenon may not be the only one responsible for this formation. In fact, researchers now suspect that, in addition to subduction, certain features of the central Andean plateau originate from sudden upward thrusts in the crust during the Cenozoic Era (the geological era that extends to -66 million today). of years). Sudden pulses that could be due to lithospheric dripping.

A conclusive experience

To test this hypothesis, the team filled a Plexiglas tank with materials that simulated Earth’s crust and mantle, using polydimethylsiloxane (PDMS), a silicon polymer about 1,000 times thicker than syrup, for the lower mantle, a mix of PDMS and modeling clay for the top. mantle, and finally a sand-like layer of tiny ceramic spheres and silica spheres for the crust.

“It was like creating and destroying mountain tectonic belts in a sandbox, floating in a simulated magma pool, all under incredibly precise sub-millimeter measured conditions”Andersen says in a press release posted on the University of Toronto website.

So, it was about reproducing the formation of a drop in this false terrestrial lithosphere, recorded with three high-resolution cameras. “The drip happens for hours, so you won’t see much happen from one minute to the next”Andersen explains. “But if you were to check every few hours, you would clearly see the change, it just takes patience.”

Comparing their results with aerial images of geological features in the Andes, the researchers found a marked similarity between the two, suggesting that the Andes were formed, at least in part, by lithospheric runoff.

“We also observed pleated crustal shortening in the model, as well as basin-like depressions on the surface, so we are confident that dripping is likely the cause of the observed deformations in the Andes.”Andersen says.

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