Scientists say the earth’s crust is “dripping” under the Andes

Beneath the Andes Mountains in South America, the Earth’s crust is falling into the planet’s interior.

Moreover, this has been happening for millions of years – a long geological process that has given rise to telltale wrinkles and other characteristics on the surface that scientists have discovered through modeling and experimentation.

This may help us determine internal geologic activity on other planets that do not have plate tectonics, such as Mars and Venus.

It’s called lithospheric dripping, and it’s been recognized fairly recently here on Earth.

When the rocky crust is heated to a certain temperature, it begins to condense and drip into the mantle. It’s a bit like a sharp drop in pitch … but the formation and release of crustal droplets have effects on the planet’s surrounding surface.

First, dragging the drop formed below creates a trough on the surface above. Then, when the fall is interrupted, the surface reacts by extruding upwards, and its effects are widespread.

“We confirmed that a deformation on the surface of an area of ​​the Andes led to the collapse of a large part of the lithosphere below,” said graduate student geology and lead author Julia Andersen at the University of Toronto, Canada.

“Because of its high density, it has been dripping like cold syrup or honey deeper into the planet’s interior and is likely responsible for two major tectonic events in the central Andes – altering the region’s surface topography by hundreds of kilometers and crushing and extending the surface crust itself.”

Geological map of the Arezaro Basin (left) and the team’s experiment (right). (DeCelles, et al.; Julia Andersen et al.)

Since scientists are only beginning to understand the distillation of the lithosphere recently, the surface response to the process has not been particularly well resolved.

But there are some features of the central Andean plateau that have been difficult to explain.

The plateau itself was formed by a subduction zone, where the edge of one tectonic plate slides down the edge of the adjacent plate. This distorts the crust, pushes it upwards, and creates mountains and other geological features.

However, there was evidence that the formation of the Central Andes was not a long and slow process, but occurred in pulsations throughout the Cenozoic Era, the Earth’s current geological period, which began about 66 million years ago.

Additionally, the timing of the rise is not consistent across the entire region, as you might expect from subduction. The Buna Plateau is higher on average than the Altiplano Plateau and contains isolated volcanic centers and basins, such as the Arizaro and Atacama basins.

“Different studies call for removal of the lithosphere to explain the large-scale surface deformation associated with non-subduction and development of plateaus,” said geologist Russell Bischlewick of the University of Toronto.

“Furthermore, crustal shortening in the interior of the Arezaro Basin is well documented by folding and local thrust faults, but the basin is not constrained by known tectonic plate boundaries, suggesting a more specific geodynamic process.”

Previous studies suggested that lithosphere dripping may have played a role, but the researchers wanted more concrete evidence.

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

The model consists of a tank and layered materials. The liquid form of a thick viscous silicone polymer called lower mantle polydimethylsiloxane. The solid upper mantle was a mixture of polydimethylsiloxane and modeling clay. Finally, a layer of sand-like balls of silica and ceramic was the counterpart to the Earth’s crust.

“It was like creating and destroying tectonic mountain belts in a sandbox, perched on a simulated basin of magma — all under very precise conditions of only millimeters,” Andersen said.

A drip “seed” was introduced into the upper mantle layer. This was slowly pulled down by gravity, a process that took hours. Meanwhile, the camera observed the whole process, taking high-resolution images every minute or so to capture the deformation of the cortex.

These images were then compared with actual geological features in the Andes.

“We compared the results of our model with geophysical and geological studies conducted in the central Andes, particularly in the Arezaro Basin, and found that changes in crustal elevation caused by drip in our models well track changes in the height of the Arezaro River. Andersen explained.”

“We also observed crustal shortening with folds in the model as well as trough-like depressions at the surface, so we are confident that dripping is the cause of the observed deformations in the Andes.”

Experiments have also shown other ways in which distillation of the lithosphere can distort the Earth’s crust. Not all of this has been observed in the Andes, which suggests that there may be other regions of the world where different types of drip can be observed, if we can identify them.

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

The search was published in Earth and Environment Communications.

Leave a Reply

%d bloggers like this: