The discovery of a mysterious patch under the Pacific Ocean that may date back to the time of dinosaurs

This previously unstudied patch of seafloor is located in the East Pacific Rise, the tectonic plate boundary on the floor of the southeastern Pacific, and sheds light on our planet’s internal processes and how its surface has changed over millions of years.

Using seismic data, geologist Jingquan Wang of the University of Maryland and his colleagues found ancient oceanic plates hidden deep in the Earth’s interior, which may contribute to seafloor spreading (marine benthic spreading), dating back to the time of the dinosaurs.

“Our discovery opens new questions about how the depths of the Earth affect what we see at the surface over vast distances and time scales,” Wang says.

By sending backscattering sound waves deep into the Earth to form seismic maps, Wang and his team identified a strange mass of mantle moving surprisingly slowly beneath the Nazca plate that borders the South American continental plate.

Most of the Earth’s volume consists of hot silicate rocks sandwiched between a thin, cold outer crust and an extremely hot core. This partially molten mineral layer is known as the mantle, and it flows in cycles over tens of millions of years due to extreme temperature differences above and below. Dense, cooler material is pulled into the warmer interior in a process called subduction.

In this region, the Nazca plate currently subducts beneath South America, but on the western side of the plate is a fast-growing ocean ridge, a hotspot of geological activity beneath the Easter Islands, and a mysterious structural divide between the central and eastern Pacific Oceans.

“We found that in this region, material was sinking at about half the speed we expected, suggesting that the mantle transition zone could act as a barrier and slow the movement of material across the Earth,” Wang explains.

The team determined that the structure of this plate is cooler and denser than the surrounding areas and appears to be a fossilized piece of ancient sea floor.

“This thick area resembles a fossilized imprint of an ancient piece of seafloor that sank into the Earth about 250 million years ago,” Wang explains. “It gives us a glimpse into Earth’s past that we never got before.”

By not melting as completely as the surrounding mantle, remnants of what was once a triple ocean floor protrude deeper into the mantle’s hotter layers, causing matter to swell into structures called superpillars.

Scientists suspect that this series of anomalies, which trend from east to west, may help tell the story of the Nazca Plate, and how it has moved throughout Earth’s history.

By deciphering the historical traces of these ancient impacts deep within the Earth, geologists can learn more about how our planet’s internal processes shaped the surface of our world today.

“Seeing the ancient subduction layer through this perspective gave us new insights into the relationship between very deep Earth structures and surface geology, which were not clear before,” Wang adds.

Source: ScienceAlert