Modelling subduction invasion of the Atlantic Ocean

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Geodynamic modelling of subduction zones : Subduction zone initiation by polarity reversal and main dynamic controls on the stability of single-sided subduction

Publication . Almeida, Jaime; Rosas, Filipe Medeiros; Riel, Nicolas

Subduction zones are one of the most widely studied geodynamic settings, representing the primary driver for mantle convection and plate tectonics. Despite this, one question still sparks controversy to the present day: how does a subduction zone initiate? Over the past half century, multiple theories have been suggested to explain subduction zone initiation (SZI). One widely cited conceptual model for SZI is polarity reversal, resulting from the shutdown of a pre-existent subduction zone due to the arrival of a buoyant block at the trench. However, the dynamic conditions by which this process occurs remain elusive. To shed light on this complex topic and assess the geodynamic constraints behind polarity reversal SZI, two geodynamic numerical modelling studies were conducted. In both studies, it was shown that this SZI mechanism is dynamically viable, without external forcing, occurring simply as the result of the evolving force balance during an oceanic plateau collision. Additionally, the efficiency of a polarity reversal event is increased by the presence of old subducting plates, relatively young overriding plates, and/or narrow oceanic plateaus. The results were shown to be consistent with a widely studied natural polarity reversal case, the collision of the Ontong-Java Plateau and formation of the Vanuatu subduction zone. Beyond the complexity of SZI, subduction zone modelling studies have predicted the existence of double-sided subduction (i.e., the simultaneous sinking of both plates) for years. As this type of subduction zone has not been found on Earth, its inexistence has been previously tied to strong subducting plates and the constant maintenance of a weak subduction interface. Additional exploratory numerical modelling was also carried out, expanding the scope of previously tested conditions by systematically exploring the effective strength contrast between the two intervening plates. The preliminary results suggest that, under top free slip conditions, two strong plates and a weak interface are needed to ensure single-sided subduction, as opposed to a strong subducting plate and a weak interface.

2022-02Tese de doutoramento

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Fundação para a Ciência e a Tecnologia

Número da atribuição

PD/BD/135067/2017