Gibraltar Subduction Zone Extending Further Into the Atlantic Ocean Could Give Rise to a New Ring of Fire

Oceans may seem eternal when compared to human lifespan, but they are actually not here for long. In fact, the concept of oceans as permanent fixtures on the surface of the Earth is challenged by the Wilson Cycle.

What Is the Wilson Cycle?

The Wilson Cycle is a model which describes the birth, growth, and closure of oceans over hundreds of millions of years. It suggests the opening and closing of ocean basins as well as the subduction and divergence of tectonic plates during the movement of supercontinents.

Using the Wilson Cycle, it is assumed that oceans, like the Atlantic were born when Pangea broke up around 180 millions years ago. A large ocean, called Tethys, also once existed between Africa and Eurasia, and led to the formation of the Mediterranean.

The model also suggests that for the oceans to stop growing and start closing, new subduction zones should form. These are the regions where one tectonic plate sinks below another. However, subduction zones are hard to form, since they require very strong plates to break and bend.

There is another way out of this "paradox", and that is by migrating subduction zones from a dying ocean in which they already exist into pristine oceans.This process is known as subduction invasion. In the case of the Atlantic Ocean, this can happen along the Mediterranean region.

Decline of the Atlantic Ocean

For the very first time, researchers from the University of Lisbon have conducted a study about the formation of such a direct invasion. The result of their investigation is reported in the paper "Gibraltar subduction zone is invading the Atlantic".

Led by researcher João Duarte from Instituto Dom Luiz, the scientists used computational, gravity-driven geodynamic 3D models to reproduce the evolution of the Western Mediterranean. They wanted to find out how the Gibraltar arc formed, and test if it is still geologically active.

The model reveals that after a period of quiescence, the arc will likely propagate farther into the Atlantic. It can also contribute to the formation of an Atlantic subduction system, which could be referred to as the Atlantic Ring of Fire. This analogy was based on the already existing structure in the Pacific. Such an event could happen 'soon' in geological terms, but not before approximately 20 million years.

The research findings also shed new light on the Gibraltar subduction zone which is still considered by some experts to be active since it has significantly slowed down in the past million years. It is assumed that the slow phase will last for another 20 million years after which it will invade the Atlantic Ocean and accelerate. This could be the beginning of the recycling of crust on the eastern side of the Atlantic and the beginning of the Atlantic itself beginning to close.

Two other subduction zones are present on the other side of the Atlantic: the Lesser Antilles in the Caribbean, and the Scotia Arc near Antarctica. These subduction zones invaded the Atlantic millions of years ago. According to Duarte, studying Gibraltar is a significant opportunity since it enables the experts to observe the invasion process in its early stages when it is just happening.