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Some parts of the Andes Mountains have characteristics that cannot be explained by the theory of plate tectonics. This has long puzzled scientists. Now, a team led by geologists University of Toronto Mystery Solved: BarThe Earth’s outer layer of rock is sinking below these regions.
According to the team, this happens because the region below the crust, the lithosphere, thickens and heats up, so it begins to “drip” downward due to gravity.
“Because of its high density, it trickled like honey into the deep interior of the planet and may have been responsible for two major tectonic events in the central Andes: changing the surface topography of the region for hundreds of kilometers and crushing and stretching the surface . . Cortex”, explains Julia Anderson, lead author of the study published in Communications Earth and Environment.
When this event occurs, is called Lithospheric drip, crustal fragments sink into the lower mantle. As a result, first a basin is formed on the surface, and then the upward movement of land occurs over hundreds of kilometers.
Lithospheric drops have previously been identified elsewhere on the planet, such as the Central Anatolian Plateau (Turkey) and the Great Basin in the western United States.
What’s going on in the Andes?
Covers part of the Central Andes territories Peru, Bolivia, Chile and Argentina. This region is defined 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 did not arise uniformly. For example, the table from Puna It is characterized by a high average elevation and includes many isolated interior basins and volcanic centers.
The Arizaro Basin, between Chile and Argentina, offers unusual geological features. Photo: Wikimedia Commons
The Arizaro Basin, located between Chile and Argentina, “is not defined by known tectonic plate boundaries, indicating that a highly localized geodynamic process is occurring,” says study co-author Russell Bysclivec.
The team suspected that lithospheric droplets had something to do with it. Indeed, previous studies have used Seismic images They found signs of this phenomenon in the region, but they did not establish a direct relationship to what is seen on the surface.
An “innovative” experiment
Anderson and his colleagues set out to recreate what happened in that vast area in their lab. Last 20 million years.
To do this, they used materials such as sand, clay and silicone to create a three-dimensional scale model to represent the Earth’s layers beneath the central Andes, “all at incredibly precise sub-millimeter scale levels,” says Anderson.
First, a tank was filled with the highly dense liquid polydimethylsiloxane (PDMS) to simulate the Earth’s lower mantle. A solid mixture of PDMS and clay was placed on top to represent the upper mantle and lithosphere. Finally, a sand-like layer made of ceramic and silica is placed on top to act as the Earth’s crust.
The scientists densified a portion of the layer of clay and PDMS (lithosphere) that began to trickle down.
A model developed by the team that simulated Earth’s layers in the central Andes. Photo: University of Toronto
“The drip happens over a few hours, so you don’t see much from one minute to the next,” says Anderson. The probe provides snapshots every 10 hours to show the progress of the leak.
The team then investigated the effects of dripping on the crustal layer and compared it with sedimentary records in the central Andes over millions of years.
They found changes in crustal height from their model were similar People from this South American region, especially the Arizaro Basin.
Comparison between the geological map of the Arizaro basin and the surface of the sample after the drip process. Photos: Julia Anderson
“We also observe bleed crustal contraction in the model and basin-like depressions at the surface, so we believe a drop is very likely. The cause of the eruptions observed in the Andes“, confirms Anderson.
“These findings show that the lithosphere may be more volatile or liquid than we thought,” says Bysklivec.
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