Geologists discover mysterious subduction zone beneath the Pacific Ocean, reshaping understanding of Earth’s interior
Scientists at the University of Maryland have discovered evidence of an ancient ocean floor that sank deep into the Earth during the age of dinosaurs, casting doubt on existing theories about the Earth’s internal structure. This previously unstudied section of the ocean floor, located on the East Pacific Rise (the plate boundary at the bottom of the southeastern Pacific Ocean), is a study of how the Earth’s internal structure and its surface have changed over millions of years. sheds new light on. The research team’s research results were published in the scientific journal Science Advances on September 27, 2024.
The team, led by geology postdoctoral researcher Jingchuan Wang, used innovative seismic imaging techniques to look deep into the Earth’s mantle, the layer between the Earth’s crust and core. They discovered an unusually thick region in the mantle transition zone, located between about 410 kilometers and 660 kilometers below the Earth’s surface. This zone separates the upper and lower mantle and expands or contracts depending on temperature. The researchers believe the newly discovered ocean floor may explain the unusual structure of the Large Pacific Low Shear Velocity Region (LLSVP), a huge region in Earth’s lower mantle. Because LLSVP appears to be divided by slabs.
“This thickened area is like a fossilized fingerprint of an ancient ocean floor that sank into the earth about 250 million years ago,” Wang said. “We’re giving you a glimpse into Earth’s past that you’ve never seen before.”
Subduction occurs when one tectonic plate slides beneath another and surface material is recycled into the Earth’s mantle. This process often leaves behind visible evidence of movement, such as volcanoes, earthquakes, and deep ocean trenches. Geologists typically study subduction by examining rock samples and sediments found at the Earth’s surface, but Wang, in collaboration with geology professor Vedran Lekic and associate professor Nicholas Schumer, used seismic waves to study subduction. and investigated the ocean floor. By studying how seismic waves travel through the different layers of the Earth, scientists were able to create detailed maps of the structures hidden deep within the mantle.
“You can think of seismic imaging as similar to a CT scan. Essentially, it allows us to see a cross-section of the Earth’s interior,” Wang said. “Normally, slabs of oceanic material are completely consumed by the Earth, leaving no discernible traces on the surface. However, viewing ancient subducted slabs through this vantage point allows us to explore the structure and surface of the very deep Earth. We now have new insights into the relationship with the geology that was previously clear.
What the research team discovered surprised them. Matter was moving much more slowly through the Earth’s interior than previously thought. Dr. Wang said the unusual thickness in this region that the research team found suggests the presence of cold material in this part of the mantle transition zone, which could be used as part of an oceanic slab sinks through the mantle. I think this suggests that we are stuck somewhere in the middle.
“We found that material is sinking at about half the rate expected in this region. This may be due to the mantle transition zone acting like a barrier, slowing the movement of material through the Earth. That suggests something,” Wang explained. “Our findings raise new questions about how the deep Earth influences what we see at the surface over vast distances and time scales.”
Looking to the future, the research team plans to expand their research to other parts of the Pacific and beyond. Wang studies ancient subduction zones and upwelling (geological processes that occur when subducted material heats up and rises to the surface again) and their effects on both the Earth’s deep and surface structures. We hope to create a more comprehensive map of impacts. Using seismic data from this study, Wang and other scientists are refining models of how tectonic plates have moved throughout Earth’s history.
“This is just the beginning,” Wang said. “We believe that deep within the Earth there are many more ancient structures waiting to be discovered. Each structure reveals many new insights about our planet’s complex past. It has the potential to lead to a better understanding of other planets beyond our own.”
The paper, “Mesozoic intraoceanic subduction shaped the lower mantle beneath the East Pacific Rise,” was published in Science Advances on September 27, 2024.
Further information: Jingchuan Wang et al, Mesozoic intraoceanic subduction shaped the lower mantle beneath the East Pacific Rise, Science Advances (2024). DOI: 10.1126/sciadv.ado1219
Provided by University of Maryland
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