Certain parts of the Cordillera de los Andes present properties that cannot be explained by theory tectonic plates. This has long intrigued scientists. Now, a team led by geologists from University of Toronto Find the answer to the riddle: barkEarth’s outermost layer of rock, sinking beneath these areas.
According to the team, this happens because the part below the crust, the lithosphere, condenses and gets hotter, so it begins to “drip” downwards due to gravity.
“Because of its high density, it drips like honey deep into the planet’s interior and may be responsible for two major tectonic events in the central Andes: changing the topography of the region’s surface by hundreds of kilometers and crushing and stretching the surface itself… of the cortex,” explains Julia Andersen, lead author of the study published in Earth and Environment Communications.
When this phenomenon occurs it is called rocky drip, crustal fragments sink into the lower mantle. As a result, a basin forms first at the surface and then an upward movement of the land mass occurs over hundreds of kilometers.
Lithosphere distillation has previously been identified elsewhere on the planet, such as the Central Anatolian Plateau (Turkey) and the Great Basin in the western United States.
What happens in the Andes?
The Central Andes include part of the territory of Peru, Bolivia, Chile and Argentina. This area 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 indicate that it did not appear uniformly. For example, file Buna plateau It has a higher average elevation and includes many isolated inner basins and volcanic centers.
One of these basins, the Aresaro Basin, located between Chile and Argentina, “is not delimited by known tectonic plate boundaries, suggesting a more specific geodynamic process has occurred,” says Russell Bischlewick, co-author of the study.
The team suspected that lithosphere dripping had something to do with it. In fact, previous studies use seismic images They discovered indications of this phenomenon in the area, but they did not establish a direct relationship like what was observed on the surface.
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An “innovative” experience
Andersen and his colleagues set out to recreate what happened in that vast region during that vast region in their lab. The last 20 million years.
To do this, they created a 3D microcosm, using materials such as sand, clay and silicon to represent the layers of the earth below the central Andes, “all in very precise sub-millimeter measurement conditions,” Andersen says.
First, a tank was filled with polydimethylsoloxane (PDMS), a very thick liquid, to simulate Underground scarf. 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, was placed on top to serve as the earth’s crust.
Scientists adsorbed part of the clay layer and PDMS (lithosphere), which began to seep to the bottom.
“Drip happens over hours, so you won’t see a lot happening from minute to minute,” Andersen says. The study provides snapshots every 10 hours to show the progress of the leak.
The team then examined the effects of distillation on the crust layer and compared them to sedimentary records in the central Andes over millions of years.
They found that changes in crustal elevation from their model They were the same Those in the South American region, particularly in the Arezzaro Basin.
“We also note shortening of the folded crust in the model, as well as trough-like depressions at the surface, so we are confident that it is very likely that The cause of the deformations observed in the Andes MountainsAndersen asserts.
“These discoveries show that the lithosphere may be more volatile or fluid than we thought,” says Pysklywec.
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