Mysterious Pacific megastructure discovered turns out to be the seafloor from the time of dinosaurs

Researchers analyzed an anomalous part of the ocean

Scientists have discovered an unusual piece of Earth deep beneath the Pacific Ocean that may explain why the world's fastest-growing ocean ridge, the East Pacific Rise, is forming in this region.

Using seismic data, geologist Jingchuan Wang and his team found ancient oceanic plates hidden in the Earth's interior that contributed to the formation of a new ocean ridge and date back to the age of dinosaurs.

“Our discovery raises new questions about how deep Earth processes influence what we observe on the surface over large distances and over time,” Wang said.

Using sound waves to create seismic maps, Wang and his colleagues identified a strange clump of mantle moving slowly beneath the Nazca Plate, which lies next to the South American continental plate.

The fact is that most of the Earth consists of heated silicate rocks, sandwiched between a cold thin crust and a hot core. This partially molten layer of minerals, called the mantle, moves cyclically over tens of millions of years due to sudden temperature changes. Denser, cooler material sinks into warmer layers in a process known as subduction.

In this region, the Nazca Plate is sinking beneath South America. However, on the western side of the plate there is a rapidly growing ocean ridge, as well as a zone of geological activity beneath the Easter Islands and a mysterious structural gap between the central and eastern Pacific Ocean.

"We found that material in this region is sinking at about half the rate expected, indicating that the mantle transition zone may act as a barrier and slow the movement of material through the Earth," explains Wang.

The team found that the structure of this plate is colder and denser than in surrounding regions, and is a fossilized fragment of an ancient seafloor.

“This thickened area resembles the fossilized trace of an ancient seafloor that sank into the Earth about 250 million years ago,” Wang adds. “This gives us a glimpse into Earth’s past that hasn’t been seen before.”

Because melting does not occur as completely as in the surrounding mantle, remnants of the ancient ocean floor from the Triassic period penetrate deeper into the hotter layers of the mantle, forming structures known as superplumes.

The researchers noted that geodynamic modeling showed that the shape and stability of lower mantle structures depend on their interaction with the subducting plate. Scientists suggest that these east-west oriented anomalies may help understand the history of the Nazca Plate and its movement throughout Earth's history.

By studying the historical traces of these ancient processes in the Earth's interior, geologists can learn more about how the inner workings of our planet shape its surface today.

“This new look at an ancient subduction plate allows us to rethink the relationship between Earth's deep structures and surface geology in a way that was not previously apparent,” Wang concludes.