Study Details Combined Tectonic and Mantle Plume Influence on King's Trough Formation

New Insights into the Formation of the King's Trough Complex Off Portugal

A recent international study has provided new insights into the formation of the King's Trough Complex (KTC), a major submarine canyon feature off the coast of Portugal.

The research suggests that the KTC's development between approximately 37 and 24 million years ago resulted from a combination of factors: the mechanical weakening of the oceanic crust due to a pre-existing mantle plume and the subsequent activity of a temporary plate boundary in the North Atlantic region.

These findings, published in Geochemistry, Geophysics, Geosystems, aim to clarify why this structure formed in its specific location.

The King's Trough Complex

The King's Trough Complex is a system of parallel trenches and deep basins extending approximately 500 kilometers in length, located off the coast of Portugal. Its easternmost point, Peake Deep, is identified as one of the deepest points in the Atlantic Ocean. Previously, scientific discussions had acknowledged tectonic processes, involving movements of the Earth's crust, as central to the KTC's formation.

Formation Mechanism

The study, led by an international team from the GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, proposes a two-stage mechanism for the KTC's formation:

Prior to the establishment of the temporary plate boundary, the oceanic crust in the region was unusually thick and thermally altered. This condition is attributed to the upwelling of hot material from the Earth's mantle, identified as an early branch of the present-day Azores mantle plume. This thickening and heating likely weakened the crust mechanically.

A temporary plate boundary then developed in this North Atlantic region, active between approximately 37 and 24 million years ago, separating the European and African plates. Researchers suggest that the pre-existing mechanically weakened crust influenced this plate boundary to shift preferentially to this area, guiding the boundary along a path of reduced resistance.

Along this boundary, the crust underwent stretching and fracturing, leading to the formation of the King's Trough.

Marine geologist Jörg Geldmacher of GEOMAR noted that the tectonic forces involved were not sustained or strong enough to create a full seafloor-spreading ridge.

The formation of the King's Trough ceased when this temporary plate boundary subsequently moved further south, towards the area of the modern Azores.

Methodology

The research utilized data collected during the M168 expedition aboard the research vessel METEOR in 2020. The methodology included:

• High-resolution sonar mapping of the King's Trough area.
• Collection of volcanic rock samples from the trench system using a chain bag dredge.
• Analysis of these samples for their chemical composition, ages, and origins, with age determination conducted at the University of Madison, Wisconsin, USA.
• Additional bathymetric data contributed by the Portuguese research centre EMEPC.
• Further contributions to the study were provided by Kiel University and Martin Luther University Halle-Wittenberg.

Broader Implications

The findings demonstrate a link between deep mantle processes and the movements of overlying tectonic plates, indicating that earlier mantle activity can influence the location of subsequent tectonic deformation.

This research contributes to a broader understanding of the geodynamic evolution of the Atlantic Ocean. Researchers suggest that the Terceira Rift in the Azores region, a comparable system of trenches currently undergoing formation within an area of unusually thickened oceanic crust, could provide further insights into how such underwater canyon networks develop under the influence of both tectonic forces and heat from Earth's interior.