According to cluster analysis of global tomographic models, the Pacific large low-shear-velocity province (LLSVP) hosts multiple internal anomalies, including a gap between the central and eastern Pacific. However, the cause of the structural gap remains unconstrained.
Directly above this structural gap, University of Maryland scientists uncovered evidence of an ancient seafloor that sank deep into Earth during the age of dinosaurs. The discovery challenges existing theories about Earth’s interior structure.
Located along the East Pacific Rise, this previously unstudied area of seafloor provides new insights into how our planet works and how its surface has changed over millions of years.
Using innovative seismic imaging techniques, scientists peered deep into Earth’s mantle. They found an unusually thick area in the mantle transition zone, about 410 and 660 kilometers below the Earth’s surface.
The zone divides the upper and lower mantles and changes size depending on temperature. The team thinks the newly discovered seafloor could help explain the unusual structure of the Pacific Large Low Shear Velocity Province (LLSVP), a vast area in the Earth’s lower mantle that seems to be divided by this slab.
Geology postdoctoral researcher Jingchuan Wang said, “This thickened area is like a fossilized fingerprint of an ancient piece of seafloor that subducted into the Earth approximately 250 million years ago. It’s giving us a glimpse into Earth’s past that we’ve never had before.”
Geologists usually study subduction by examining rock samples and sediments found on Earth’s surface. In this study, scientists used seismic waves to investigate the ocean floor. They examined how seismic waves traveled through different layers of Earth. Based on their observations, they created detailed mappings of the structures hiding deep within the mantle.
Wang said, “You can think of seismic imaging as something similar to a CT scan. It’s allowed us to have a cross-sectional view of our planet’s insides. Usually, the Earth consumes oceanic slabs of material completely, leaving no discernible traces on the surface.”
“But seeing the ancient subduction slab through this perspective gave us new insights into the relationship between very deep Earth structures and surface geology, which were not obvious before.”
The findings were extremely surprising: The material movement was much slower than previously believed. The unusual thickness of this area suggests the presence of colder material in this part of the mantle transition zone. This means that some oceanic slabs get stuck halfway down as they sink through the mantle.
Wang explained, “We found that in this region, the material was sinking at about half the speed we expected, which suggests that the mantle transition zone can act like a barrier and slow down the movement of material through the Earth. Our discovery raises new questions about how the deep Earth influences what we see on the surface across vast distances and timescales.”
The team plans to expand its research to other areas of the Pacific Ocean and beyond. Wang hopes to create a more detailed map of ancient subduction and upwelling zones—geological processes where subducted material heats up and rises to the surface.
This research will help them understand how these zones affect deep and surface Earth structures. With the seismic data collected, Wang and other scientists are improving their models of tectonic plate movements throughout Earth’s history.
Wang said, “This is just the beginning. We believe many more ancient structures are waiting to be discovered in Earth’s deep interior. Each one has the potential to reveal many new insights about our planet’s complex past—and even lead to a better understanding of other planets beyond ours.”
Journal Reference:
- Jingchuan Wang, Vedran Lekic et al. Mesozoic intraoceanic subduction shaped the lower mantle beneath the East Pacific Rise. Science Advances. DOI: 10.1126/sciadv.ado1219