Subduction Zone in 'Embryonic' Stage Discovered off Portugal Coast

Evidence of a newly active subduction zone off the coast of Portugal has caught the interest of geologists eager to witness what the beginning of a great continental shift looks like in the preliminary stage.

Over the course of about 20 million years, the subduction zone will be responsible for compressing the Atlantic Ocean as continental Europe moves closer to North America. Geologists from Monash University discovered evidence that a passive margin -- an area along a coastline where no collision or subduction is taking place -- is becoming active. The find will enable geologists to observe the beginnings of a tectonic shift, much like biologists can observe a growing fetus from the embryonic stage forward.

"What we have detected is the very beginnings of an active margin - it's like an embryonic subduction zone," João Duarte, lead author of the study on the new subduction zone, which was discovered after mapping of the ocean floor on the Southwest Iberia plate margin revealed fracturing, indicating tectonic activity.

Active margins are commonly sights of tectonic activity such as earthquakes, volcanoes and mountain building that involve a continental plate crashing into an oceanic plate.

"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," Duarte said.

The "embryonic" subduction could indicate the beginnings of a new phase of the Wilson Cycle - where plate movements break up supercontinents and open oceans, then stabilize them to form new subduction zones, which will close the oceans and bring the scattered continents back together. The breaking up and reformation of supercontinents is thought to have happened at least three times in the past 4 billion years on Earth. The last supercontinent was Pangea, which formed about 300 million years ago. In this case, the Iberian subduction will gradually pull Iberia toward the United States over approximately 220 million years. 

Even though the newly active margin is just beginning to show activity, Duarte says the site will yield data that will assist in refining the current geodynamic models.

"Understanding these processes will certainly provide new insights on how subduction zones may have initiated in the past and how oceans start to close," Duarte said.