Sink or Swimming: The fate of a sinking structural plate depends on the history of ancient structures

Newly published studies have revealed that anomalies in compositional rocks in marine plates caused by ancient tectonics affect plate trajectories and velocity as they plunge deep into the Earth’s mantle.

Between 410-660km of depth is the Mantle Transition Zone (MTZ), a key area that acts as a gateway for material entering the Earth’s deeper mantle. The large distribution of basalt rock composition within the MTZ can cause subduction plates (those that slide under others) to slow and stagnate within this zone rather than descend directly into the lower mantle. The basalt reservoir has been previously discovered in the MTZ, but its origin remains unknown.

An international team of seismologists led by the University of Southampton (and now located at the Woods Hole Marine Facilities) provided evidence of a very thick MTZ. This can only be explained by the large basaltic rock composition, suggesting that in certain areas, the entire marine slab of 100 kilometres thick has important basaltic material.

Findings published in the Nature Journal recycle deep surface materials and volatile elements inside the Earth to provide a deeper understanding of long-term climate stability, air balance, and billions of years of planetary habitability.

The study is part of the Voila (Lesser Antilles Volatiles) project, where the team deployed 34 seismometers on the seabed below the Antilles.

“This was the first large-scale submarine seismic experiment to be carried out in the Atlantic subduction zone,” said Dr. Katherine Reichert, formerly an associate professor at the University of Southampton and now at the Woods Hole Institute of Oceanography. “We were very surprised to find an unexpected and very thick mantle transition zone under the Antilles, an outline of 330km. This makes it one of the thickest transition zones observed worldwide. The Caribbean is well known for its sun and beaches, but now claims it is praised in the world of plate tectonics.”

“In some ways, structural plates have a ‘memory’ and it’s wild to think that it will affect the way plates drive convection in the mantle and return to Earth,” said Dr. Nick Harmon, formerly an associate professor at the University of Southampton and now at the Marine Facility in Woods Hole.

The lead author, Dr. Xusong Yang, a former visiting scholar at the University of Southampton, and currently visiting scholar at the University of Miami, stated, “We cannot overlook the heterogeneity of the inherited composition of subducting marine slabs.