Latin America: Earth’s crust under the Andes is sinking -study

Geologists have discovered a sinking of the Earth’s crust under the Andes. The study has confirmed that the part under the rock layer is “seeping” deep into the planet, which explains some of the features of the mountains.

Certain parts of the Andes have features that the plate tectonics theory cannot explain. It has long puzzled scientists. Now a team led by geologists at the University of Toronto has found the answer to the riddle: The crust, the Earth’s outermost layer of rock, is sinking beneath these areas.

According to the team, this happens because the part under the crust, the lithosphere, thickens and heats up, causing it to “leak” downward due to gravity.

“Because of its high density, it drips like honey into the deep interior of the planet and is likely responsible for two major tectonic events in the central Andes: changing the surface topography of the region by hundreds of kilometers and flattening and stretching the crustal surface itself,” explains Julia Andersen, lead author of the study published in Communications Earth & Environment.

In this phenomenon, called lithospheric drift, crustal fragments sink into the Earth’s lower mantle. As a result, a basin first forms at the surface, and then the land mass moves upward for hundreds of kilometers. Lithospheric drift has been detected elsewhere on Earth, such as in the central Anatolian Plateau (Turkey) and the Great Basin in the western United States.

WHAT IS HAPPENING IN THE ANDES?

The central Andes include parts of Peru, Bolivia, Chile, and Argentina. This region is bounded by the Puna and Altiplano plateaus and was formed millions of years ago when the Nazca Plate slid under the South American Plate.

However, its unusual features suggest that it was not formed uniformly. The Puna Plateau, for example, is characterized by a higher average elevation and includes several isolated inland basins and volcanic centers.

One of these basins, the Arizaro Basin between Chile and Argentina, “is not defined by known tectonic plate boundaries, suggesting that it is a more localized geodynamic process,” explains Russell Pysklywec, co-author of the study.

The team suspected that lithospheric drip had something to do with it. Previous studies using seismic imagery have detected evidence of this phenomenon in the region but have not directly linked it to what is observed at the surface.

A “GROUNDBREAKING” EXPERIMENT

Andersen and his colleagues set out to recreate in their laboratory what had been happening in this vast region over the past twenty million years.

They developed a three-dimensional model representing the Earth’s layers beneath the central Andes using materials such as sand, clay, and silicon “under incredibly accurate submillimeter measurement conditions,” Andersen said.

First, a tank was filled with polydimethylsiloxane (PDMS), a very thick liquid, to simulate the Earth’s lower mantle. On top of that, a solid mixture of PDMS and clay was applied to represent the upper mantle and lithosphere. Finally, a sand-like layer of ceramic and silica was applied to serve as the Earth’s crust.

The scientists compacted a portion of the clay and PDMS layer (lithosphere), which began to leak downward. “The dripping occurs over hours, so you don’t see much from one minute to the next,” Andersen says. The study presents snapshots every ten hours to show the progress of the trickle.

The team then examined the effects of the trickle on the crustal layer and compared it to the sediment record in the central Andes over millions of years. They found that the changes in crustal height in their model were similar to those in this South American region, particularly in the Arizaro Basin.

“We also observed crustal shortening with folds in the model, as well as basin-like depressions at the surface, so we are confident that a drop is very likely the cause of the observed deformations in the Andes,” Andersen affirms. “These results indicate that the lithosphere may be more volatile or fluid than we thought,” Pysklywec said.

With information from Latina Press

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