Does the Horseshoe Abyssal Plain represent the start of a new subduction zone?

An image of the Earth to illustrate the concept of the oceanic lithosphere and theHorseshoe Abyssal Plain which may be the start of a new subduction zone.
© iStock/MarcelC

A team of geologists at the European Geosciences Union meeting suggested that the Horseshoe Abyssal Plain may represent the start of a new subduction zone.

The team assessed the Horsehoe Abyssal Plain, and answered the question of whether earthquakes were the result of the process of a new subduction zone being created. They argue that old oceanic lithosphere could perform a vital role in this process.

How did the earthquake occur in a flat abyssal region?

According to, the leader of the team of geologists, João Duarte, noted that ever since the 1969 earthquake off the coast of Portugal he has wondered how the earthquake occurred due to it not being part of a subduction zone.

It adds that Duarte explained: “Some in the field suggested it could be the start of a subduction zone. Then, last year, another team conducted high-resolution imaging of the area and also found evidence of the mass, confirming that it truly existed.”

In the abstract, the authors write:”Intriguingly, the epicenter of the 1969 earthquake occurred in a relatively flat abyssal region, far from any known tectonic faults with significant length and surface expression.”

The oceanic lithosphere

The authors add: “Preliminary results show that indeed, under certain circumstances, the existence of a serpentinized layer in old oceanic lithosphere may generate horizontal decoupling zones that can lead to the delamination of old oceanic lithosphere. In the present case, due to the proximity to a continental margin and to the Azores-Gibraltar Plate Boundary the process is highly asymmetric and resembles simple models of subduction initiation. We propose that the reactivation of the margin and the hypothetical process of subduction initiation may have been aided by a process of delamination of oceanic lithosphere.”

The authors argue that the finding will contribute to scientific understand of the oceanic lithosphere and plate tectonics. They write: “the identification of a first case of oceanic lithospheric delamination will certainly contribute to further our understanding of the dynamics of tectonic plates. Old oceanic lithosphere may be prone to gravitational instabilities, which may play a fundamental role in the process of subduction initiation.”

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