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The subduction zone below the Gibraltar Strait is sleeping. However, it could become active and break into the Atlantic Ocean after millions of years.
Sleeping Subduction Zone Could Awaken and Break Into the Atlantic Ocean
A new study suggests that a subduction zone below the Gibraltar Strait is moving westward and could one day "invade" the Atlantic Ocean, resulting in the ocean's gradual closure. The Gibraltar arc or trench subduction zone is located between Portugal and Morocco in a slender oceanic corridor.
Its westward progress slowed in the last 5 million years, leading some scientists to wonder if the Gibraltar arc is still active today. It started about 30 million years ago when a subduction zone formed along the northern shore of what is now the Mediterranean Sea.
But it seems like the arc is just at a quiet phase right now. This interlude is expected to endure for a further 20 million years, following which the Gibraltar arc may recommence its upward motion and breach the Atlantic, a phenomenon referred to as "subduction invasion."
After modeling the arc's course for the next 40 million years, the scientists discovered that starting from the present, it must laboriously make its way through the tiny Gibraltar Strait over the next 20 million years. According to the researchers, the subduction zone extends and spreads oceanward beyond this location, and the trench retreat gradually quickens.
"These subduction zones invaded the Atlantic several million years ago," lead author João Duarte, a geologist and assistant professor at the University of Lisbon, said in a statement. "Studying Gibraltar is an invaluable opportunity because it allows observing the process in its early stages when it is just happening."
If the Gibraltar arc penetrates the Atlantic, it may help construct an Atlantic subduction system akin to the Ring of Fire, a series of subduction zones around the Pacific Ocean. The oceanic crust would gradually engulf and close this ocean as a comparable chain formed in the Atlantic would cause the oceanic crust to be recycled into the mantle by subduction on both sides of the Atlantic.
The relative lack of seismicity and volcanism in the area, which have been presented as reasons to rule out the possibility that the subduction zone is still active, may be explained by the Gibraltar arc's grinding advance over the previous five million years. The new study's authors contend that the subduction zone's prolonged period of stopped movement is the primary cause of its tectonic stillness.
The Great Lisbon Earthquake of 1755, estimated to have a moment magnitude of between 8.5 and 9.0, was the last significant earthquake to shake the area, despite several lesser ones having since been reported. Experts say the likelihood of an earthquake of this scale happening anytime soon is "pretty much out of the question, since the last such tremendous event was only 250 years ago."
What Is Subduction Invasion?
Subduction is the action that occurs when two tectonic plates collide at convergent boundaries, and one of the plates slides beneath the other due to gravity and density variations. The subduction zone is the boundary region where this happens.
Subduction invasion is the earliest stage of the subduction process. This process involves the formation of a new subduction zone in an exterior ocean and its subsequent migration to an interior ocean, which is a crucial process in the geological evolution of our planet. This process is probably common to seas of the Atlantic type.
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