Sink or Swim: The fate of sinking tectonic plates depends on their ancient tectonic histories

Between depths of 410 and 660 kilometers lies the mantle transition zone (MTZ), a critical region acting as a gateway for materials entering Earth's deeper mantle. Large distributions of basalt rock compositions within the MTZ can cause subducting plates -- ones that slide beneath other -- to slow and/or stagnate within this zone, instead of descending directly into the lower mantle. Although basalt reservoirs have previously been discovered in the MTZ, their origins have remained unclear.

An international team of seismologists led by the University of Southampton (and now at the Woods Hole Oceanographic Institution) has provided evidence of an extremely thick MTZ, which can only be explained by a large basaltic rock composition, suggesting that, in certain regions, entire oceanic slabs -- approximately 100 kilometers thick -- can possess significant basaltic material.

The findings, published in the journal Nature, provide a greater understanding of plate subduction, which recycles surface materials and volatile elements deep into the Earth's interior, sustaining long-term climate stability, atmospheric balance, and the habitability of our planet over billions of years.

This groundbreaking research is part of the VoiLA (Volatiles in the Lesser Antilles) project, in which the team deployed 34 seismometers on the ocean floor beneath the Lesser Antilles.

"This is the first large scale ocean bottom seismic experiment conducted at an Atlantic subduction zone," said Dr. Catherine Rychert, formerly an Associate Professor at the University of Southampton and currently at the Woods Hole Oceanographic Institution. "We were very surprised to find an unexpected and exceptionally thick -- approximately 330 kilometers -- mantle transition zone beneath the Antilles, which makes it one of the thickest transition zones observed worldwide. Although the Caribbean is well-known for its sunshine and beaches, it now has a new claim to fame in the world of plate tectonics."

"It's wild to think that in some ways tectonic plates have a 'memory' and that affects the way the plates drive mantle convection and mix material back into the Earth," said Dr. Nick Harmon, formerly an Associate Professor at the University of Southampton and currently at the Woods Hole Oceanographic Institution.

"It's wild to think that in some ways tectonic plates have a 'memory' and that affects the way the plates drive mantle convection and mix material back into the Earth," said Dr. Nick Harmon, formerly an Associate Professor at the University of Southampton and currently at the Woods Hole Oceanographic Institution.

Lead author, Dr. Xusong Yang, a former visiting scholar at the University of Southampton and currently at University of Miami, emphasized, "We cannot overlook the inherited compositional heterogeneity of subducting oceanic slabs. It may greatly influence their ultimate fate in Earth's deep interior."

Dr. Kate Rychert and Dr. Nick Harmon, formerly of the University of Southampton, Professor Saskia Goes from Imperial College London, and Professor Andreas Reitbrock from Karlsruhe Institute of Technology, led the experiment. The experiment was funded by NERC (Natural Environment Research Council, UK) and the ERC (European Research Council).