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Scientists are reconstructing ancient sunken plates under the Andes

The Andes are the longest contiguous mountain range in the world and extend about 7,000 kilometers along the west coast of South America. The edge of the Andes, where two tectonic plates meet, has long been considered a textbook example of a steady, continuous subduction event in which one plate was pushed under the other and ultimately formed the mountain range that can be seen today. Geologists the University of Houston demonstrate in a paper published in the journal Nature the reconstruction of the subduction of the oceanic Nazca Plate, the remains of which are currently found up to 1,500 kilometers below the earth's surface.

Their results show that the formation of the Andean Mountains was more complicated than the previous models suggested.
“The Andean mountain formation has long been a prime example of plate tectonics,” said Jonny Wu, assistant professor of geology at UH and co-author of the study.

When tectonic plates move beneath the earth's crust and get into the mantle, they don't go away. Rather, they sink towards the core, like leaves sinking to the bottom of a lake. As these plates sink, they retain part of their shape and provide insight into the surface of the earth millions of years ago.
These plate remnants can be imaged with the help of earthquake waves, similar to the way in which CT scans enable doctors to see the inside of a patient. “We tried to go back in time with more accuracy than anyone has ever done before. This has resulted in more detail than previously thought possible, ”said Wu. "We managed to go back to the time of the dinosaurs."

Nazca plate subduction

The paper describes the deepest and oldest plate remains that have been reconstructed to this day. The plates are from the Cretaceous Period. "We found evidence that when the plate reached the transition zone, it was generating signals on the surface," said Yi-Wei Chen, PhD student in geology at the UH College of Natural Sciences and Mathematics and first author a work. A transition zone is a discontinuous layer in the Earth's mantle that, when hit by a sinking plate, slows the movement of the plate and causes higher accumulation over it.

In addition to Wu and Chen, John Suppe, Distinguished Professor of Earth and Atmospheric Sciences at UH, is co-author of the paper.
The researchers also found evidence for the idea that instead of steady, continuous subduction, the Nazca plate was temporarily torn off from the Andean rim, leading to volcanic activity. To confirm this, they modeled volcanic activity along the Andean rim. "We were able to test this model by looking at the pattern from over 14,000 volcanic records along the Andes," said Wu.

The work was carried out as part of the UH Center for Tectonics and Tomography, which is led by Soup.
“The Center for Tectonics and Tomography brings together experts from various fields to relate tomography, the representation of the Earth's interior from seismology to the study of tectonics,” said Wu. "For example, the same techniques we use to explore these lost plates are adapted to petroleum exploration techniques."

publication: Southward propagation of Nazca subduction along the Andes,Nature (2019). DOI: 10.1038 / s41586-018-0860-1, www.nature.com/articles/s41586-018-0860-1

source: off. Pm from the University of Houston

Title caption: The researchers from the University of Houston John Soup, left, Jonny Wu and Yi-Wei Chen have reconstructed the old plates under the Andes. (Source: University of Houston)