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A new active fault system has been discovered off the coast of Portugal, which scientists believe could be the first signs of an eventual convergence of the North American and Eurasian tectonic plates.

Geologists from Monash University mapped the ocean floor off the coast of the Iberian Peninsula, finding the evidence for what lead author João Duarte described as "an embryonic subduction zone".


These subduction zones are where one tectonic plate dives underneath another one to be destroyed, often causing earthquakes in the process. Portugal has experienced huge earthquakes in the past -- the Lisbon quake of 1755 was one of the worst in world history, killing between 10,000 and 100,000 people -- and these normally occur near convergent plate boundaries.

Duarte said: "Significant earthquake activity, including the 1755 quake which devastated Lisbon, indicated that there might be convergent tectonic movement in the area. For the first time, we have been able to provide not only evidences that this is indeed the case, but also a consistent driving mechanism."

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The results, published in the journal Geology, show that there is a complex interplay between the Eurasian, African and North American plates that could see Iberia and North America move together.

The Atlantic Ocean is currently getting wider at the mid-Atlantic Ridge, a divergent plate boundary that pushes the Old and New Worlds apart at a rate of around 2.5cm per year. This ridge runs along what was once the very centre of the supercontinent Pangaea, 180 million years ago.

However, this new subduction zone near Portugal becoming active could signal the very first steps of that process of separation reversing -- one of the stages of the hypothesised "supercontinent cycle". This theory holds that the Earth's plates routinely form into, and break out of, giant supercontinents over the course of hundreds of millions of years. Pangaea was the most recent of these.


Currently, both the African and Eurasian plates are moving away from the North American and South American plates, but at the same time the African plate is moving north, into the Eurasian plate -- this is why the Alps exist. Small subduction zones have already been found in the Mediterranean, near Gibraltar, that are migrating as this happens.

The new study adds to this knowledge and proposes that, in an estimated 220 millions years, the North American plate will begin moving towards the Eurasian plate again as a new supercontinent begins to appear, with the Atlantic Ocean disappearing into the new subduction zone near Portugal.

However, it will take 20 million years for the new fault to become truly active, so we're in for a long wait to see if that is what will happen.