Anomaly in the Atlantic Ocean may be the first detection of a tectonic plate stripping


Scientists have identified what they say is the first evidence of a tectonic plate shelling in two separate layers under the ocean.

This epic but still hypothetical division – insofar as we can detect it in computer modeling – could be responsible for the birth of a new subduction zone, where one of the Earth's tectonic plates is thrust forcefully under another.

The marine geologist João Duarte of the University of Lisbon in Portugal studies the seismic history of his hometown for years, characterized by the Great Lisbon Earthquake of 1755: a catastrophic earthquake and tsunami that erased Lisbon, killing up to 100,000 people in the process.

Centuries later, a much milder event in 1969 in the same region was also observed by seismologists, but fortunately it did not claim human lives.

However, what is strange is that these violent tremors are happening, since the region from which they come is a sparse and abyssal plain on the seabed along the Iberian Peninsula, far from any active tectonic faults.

015 iberia subduction tectonic plate portugal 1(Duarte et al., Geology, 2013)

But far below this flat and nothing remarkable landscape of the sea bed, something else is happening, Duarte says: something seismic.

"This seismicity is located below a seismically silent layer, interpreted as a serpentine front that propagates through the upper lithosphere mantle," Duarte and his team write in summary for a new poll presented last month at the EGU General Assembly in Vienna .

Serpentination is a geological process where rocky structures absorb water and, according to researchers, may be responsible for the oceanic lithosphere off the coast of Portugal, peeling in two, potentially triggering earthquakes as it breaks.

"Several tomographic models have consistently imagined a high-speed anomaly stretching to a depth of 250 kilometers, just below this cluster of seismicity," write the researchers.

"We interpret this anomaly as a lithosphere drip caused by the delamination of the oceanic lithosphere. If that is the case, it is the first time that the delamination of the oceanic lithosphere is identified."

By testing their hypotheses with computational models, researchers' early work – which has not yet been peer reviewed – suggests that a serpentine layer in the ancient oceanic lithosphere could generate "horizontal decoupling zones" across the oceanic plate, leading to more rock low and softer layer to delaminate & # 39; (tear) of the top layer.

If they are right – and that's a big one for now – the researchers propose that this phenomenon could be helping to create a subduction zone in the region, where one tectonic plate ends up being led by another.

"Today, we know that the Iberian margin of the Southwest is actually being reactivated," Duarte explained in a post last year.

"Whether this will lead to the nucleation of a new subduction zone is still a matter of debate, and we will probably never know for sure. However, subduction initiation is one of the main unresolved problems in Earth science, and the coasts of Lisbon can be a perfect natural laboratory to investigate this problem. "

Taken to an extreme, this process of subduction initiation could, hypothetically, help to ground the foundations of an entirely new supercontinent.

In a research published in 2016, Duarte and his colleagues proposed a new conceptual model based on the old and unstable oceanic lithosphere, in which "both the Pacific Ocean and the Atlantic close simultaneously, leading to the termination of Earth's current supercycle and the formation of a new supercontinent, which we call aurica. "

This distant future – if that will happen – is many millions of years old, but Duarte is enthusiastic about the possibilities.

"It's a great statement," said Duarte National Geography. "Maybe this is not the solution to all the problems, but I think we have something new here."

The conclusions were presented at the EGU General Assembly in Vienna in April.


Source link