Earth’s crust is ‘draining’ under the Andes

(ORDO NEWS) — Under the Andes mountains in South America, the earth’s crust seeps deep into the planet.

What’s more, it’s been happening for millions of years, a long geological process that has produced noticeable wrinkles and other features on the surface that scientists have identified through modeling and experimentation.

This could help us determine internal geologic activity on other planets that don’t have plate tectonics, like Mars and Venus.

This phenomenon is called lithospheric dripping, and it was revealed quite recently on Earth.

When the rocky crust is heated to a certain temperature, it begins to thicken and drain into the mantle. It’s a bit like an extreme drop in altitude… but the formation and ejection of crustal droplets has an impact on the planet’s surrounding surface.

First, the pull of a drop forming below creates a pool on the surface above. Then, when the drop breaks off, the surface reacts with an upward springy movement, the effects of which are widely distributed.

“We have confirmed that a significant portion of the lithosphere below is avalanched when the surface of one of the Andes Mountains deforms,” ​​said geology graduate student and lead author of the study, Julia Andersen, from the University of Toronto in Canada.

“Due to its high density, it, like cold syrup or honey, flowed deeper into the bowels of the planet and is probably responsible for two major tectonic events in the Central Andes – a shift in the topography of the region’s surface by hundreds of kilometers and at the same time the crunch and stretching of the surface crust itself.”

Since scientists have only recently begun to understand what lithospheric drift is, the response of the surface to this process is not particularly well understood.

But there are some features of the Central Andean Plateau that are difficult to explain.

The plateau itself was formed by a subduction zone, where the edge of one tectonic plate slides under the edge of an adjacent plate. This deforms the crust, pushing it up and creating mountains and other geological features.

However, there is reason to believe that the formation of the Central Andes was not a long and slow process, but occurred in impulses throughout the Cenozoic era, the modern geological period of the Earth, starting from about 66 million years ago.

In addition, uplift times do not match across the region, as would be expected from subduction. The Puna Plateau is higher on average than the Altiplano Plateau and contains volcanic centers and isolated basins such as the Arizaro and Atacama basins.

“Various studies have suggested removal of the lithosphere to explain widespread, non-subduction-related surface deformation and plateau evolution,” says geologist Russell Pisklivets of the University of Toronto.

“In addition, crustal shortening in the interior of the Arizaro Basin is well documented by folding and local thrust faulting, but the basin is not limited by known tectonic plate boundaries, indicating a more localized geodynamic process.”

Previous research had suggested that lithospheric drift might be involved in this process, but the researchers wanted more concrete evidence.

They designed a laboratory experiment in which they built models of the earth’s crust and upper mantle to observe what happens on the surface when the crust begins to drip.

The model consisted of a reservoir and layered materials. A thick, viscous liquid of silicone polymer called polydimethylsiloxane formed the lower mantle.

The solid upper mantle was a mixture of polydimethylsiloxane and modeling clay. Finally, a layer of sand-like spheres of silica and ceramics was analogous to the earth’s crust.

“It was like the creation and destruction of tectonic mountain belts in a sandbox, floating in a simulated magma pool – all under incredibly precise submillimeter conditions,” Andersen said.

The drip “seed” was inserted into the top layer of the mantle. Under the influence of gravity, it slowly pulled down, and this process took several hours. During this time, the camera monitored the entire process, taking high-resolution pictures every minute or so to capture the deformation of the crust.

Earths crust is draining under the Andes 2
These images were then compared with real geological features in the Andes

“We compared the results of our model with geophysical and geological studies conducted in the Central Andes, in particular in the Arizaro Basin, and found that changes in crustal height caused by drip flow in our models match very well with changes in height in the Arizaro Basin,” Andersen explained.

“We also observed shortening of the crust with folds in the model, as well as basin-like depressions on the surface, so we are confident that the drip is very likely to be the cause of the observed deformations in the Andes.”

The experiments also showed other ways in which lithospheric dripping can deform the Earth’s crust. Not all of them have been observed in the Andes, which suggests that there may be other regions of the world where various types of drop formation can be observed, if we can identify them.

In turn, this also suggests that non-subduction processes may play a larger role than we thought in shaping our planet’s surface.


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