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
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
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
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.