Geologists discover mysterious subduction zone beneath the Pacific, reshaping understanding of Earth’s interior

Scientists at the University of Maryland have discovered evidence of an ancient sea floor that sank deep into the Earth during the age of dinosaurs, challenging existing theories about Earth’s interior structure. Located in the East Pacific Rise (a tectonic plate boundary at the bottom of the southeast Pacific Ocean), this previously unstudied portion of the seafloor sheds new light on the inner workings of our planet and the how its surface has changed over millions of years. The team’s findings were published in the journal Scientific advances on September 27, 2024.

Led by geology postdoctoral researcher Jingchuan Wang, the team used innovative seismic imaging techniques to peer deep into Earth’s mantle, the layer between our planet’s crust and core. They discovered an unusually thick zone in the mantle transition zone, a region between 410 and 660 kilometers below the Earth’s surface. The zone separates the upper and lower mantles, expanding or contracting depending on temperature. The team believes the newly discovered seafloor could also explain the anomalous structure of the Low Shear High Velocity Pacific Province (LLSVP) – a massive region in Earth’s lower mantle – because the LLSVP appears to be split by the slab .

“This thickened area looks like the fossilized fingerprint of an ancient piece of seafloor that buried itself in the Earth about 250 million years ago,” Wang said. “It gives us a glimpse into Earth’s past that we’ve never had before.”

Subduction occurs when one tectonic plate slides beneath another, recycling surface materials into the Earth’s mantle. The process often leaves visible traces of movement, including volcanoes, earthquakes and deep sea trenches. While geologists typically study subduction by examining rock samples and sediments found on Earth’s surface, Wang worked with geology professor Vedran Lekic and associate professor Nicholas Schmerr to use seismic waves to probe the bottom oceanic. By examining how seismic waves passed through different layers of the Earth, scientists were able to create detailed maps of structures hidden deep within the mantle.

“You can think of seismic imaging as something similar to a scanner. It basically allows us to have a cross-sectional view of the interior of our planet,” Wang said. “Usually, slabs of ocean material are completely consumed by Earth, leaving no discernible trace on the surface. But seeing the ancient subducting plate from this angle gave us new insights into the relationship between very deep Earth structures and surface geology, which were not evident before.

What the team discovered surprised them: Matter moved inside the Earth much more slowly than previously thought. Wang thinks the unusual thickness of the area the team discovered suggests the presence of colder material in this part of the mantle transition zone, hinting that some ocean slabs get stuck midway as they move. penetrate through the coat.

“We found that in this region, material flowed at about half the speed we expected, suggesting that the mantle transition zone may act as a barrier and slow the movement of material through the Earth,” Wang said. “Our discovery opens new questions about how Earth’s depths influence what we see on the surface over vast distances and time scales.”

Looking ahead, the team plans to expand their research to other areas of the Pacific Ocean and beyond. Wang hopes to create a more complete map of ancient subduction and upwelling zones (the geological process that occurs when subducted material heats up and rises to the surface), as well as their effects on deep and surface Earth structures. Using the seismic data acquired during this research, Wang and other scientists are improving their models of how tectonic plates have moved throughout Earth’s history.

“This is just the beginning,” Wang said. “We believe there are many other ancient structures waiting to be discovered deep within the Earth. Each of them has the potential to reveal many new insights into our planet’s complex past and even lead to a better understanding of other planets beyond our own.”

The paper titled “Mesozoic intraoceanic subduction shaped the lower mantle beneath the rising East Pacific” was published in Scientific advances on September 27, 2024.