A new study suggests that the oceanic plate next to Portugal could be peeling apart in a process that may result in the disappearance of the Atlantic Ocean and the creation of a new supercontinent.
On November 1, 1755, a giant 8.7 magnitude earthquake struck off the coast of Portugal, destroying the city of Lisbon. The seismic event and the following tsunami triggered the interest of philosophers and contributed to the development of modern seismology.
aIn 1969, a 7.9 magnitude earthquake struck in the same region. This was the time when the theory of plate tectonics was developed, and several scientists came to study this margin.
Since then, many studies have been dedicated to the Atlantic southwest passive margin of Portugal and several scientists proposed that this region was a case of subduction initiation, marine geologist Joao C. Duarte from the University of Lisboa's Instituto Dom Luiz (IDL) notes.
Intriguingly, the epicenter of the 1969 earthquake occurred in a relatively flat abyssal region, far from any known tectonic faults with significant length and surface expression. Previous studies showed the existence of a seismicity cluster precisely in this area at lithospheric mantle depths of ∼50 km (31 miles), in a section of old oceanic (Jurassic?) lithosphere.
According to the studies made by Duarte and his scientist's team, this seismicity is located below a seismically silent layer, interpreted as a serpentinization front propagating down through the lithospheric upper mantle.
Several tomographic models have consistently imaged a fast-velocity anomaly extending up to a depth of 250 km (155 miles), right below this seismicity cluster.
The team interpreted the anomaly as a lithospheric drip caused by the delamination of oceanic lithosphere.
If this is the case, it is the first time that delamination of oceanic lithosphere is identified.
"We propose that the reactivation of the margin and the hypothetical process of subduction initiation may have been aided by a process of delamination of oceanic lithosphere," Duarte said.
According to the data presented on computer simulations at the European Geosciences Union meeting, the development of these events could provide 'the necessary spark for one plate to start grinding under another in what's known as a subduction zone,' Duarte pointed.
Oceans are born and then they spread, before eventually closing up to form a new supercontinent, in what is known as the super-continental cycle, Duarte said. "The Atlantic, for example, was formed from the breakup of the supercontinent Pangea, then 'spread' to assume its current form."
The team made an assumption that Atlantic is now closing in a process which will, in about 200 million years, end up creating a new supercontinent.
Fabio Crameri, a scientist from the University of Oslo (who hasn't been a part of the study), said Duarte presented some strong arguments, adding that the model needs further testing, which is not an easy feat when your data comes from a natural process that works at the speed at which fingernails grow.
Featured image credit: Rafael Wagner
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