Scientists discover tectonic ‘mega-plate’ that disappeared 20 million years ago

For millions of years, Earth’s shifting plates have shaped continents, formed oceans, and built towering mountain ranges. But some of these colossal structures have vanished into the depths of the planet’s mantle, seemingly lost to time.

Now, scientists have uncovered one of these missing pieces—the Pontus plate—shedding new light on Earth’s geological past and how the planet continues to evolve.

The Earth’s crust is divided into large, rigid tectonic plates that move over time, driving earthquakes, volcanic activity, and the formation of continents. Since the breakup of the supercontinent Pangea during the late Paleozoic, plate movements have been primarily organized into two distinct realms.

In the Tethyan realm, enclosed by the continents of Pangea, oceanic plates formed and subducted along predominantly east-west ridges and trenches.

Meanwhile, in the Panthalassa realm, which surrounded Pangea, subduction occurred radially outward, pulling oceanic plates beneath continental margins and creating complex geological interactions.

At the boundary between these two systems, known as the Junction Region, the interaction of plates was especially complicated. Stretching from Australia to Eurasia, this region saw the formation and disappearance of multiple subduction zones and oceanic basins.

Many of these structures were eventually lost, leaving behind only fragments preserved in today’s mountain ranges and ocean floors. These remnants provide clues to reconstruct the geological past and understand the forces that drive plate movements.

One of the most significant recent discoveries in plate tectonics is the confirmation of the Pontus plate, which once covered 15 million square miles—about a quarter of the Pacific Ocean.

For millions of years, it was believed to have been completely consumed by subduction, the process in which one tectonic plate sinks beneath another into the mantle. But traces of its existence remained hidden in the geological record.

Dr. Suzanna Van de Lagemaat and her team at Utrecht University led the groundbreaking study that confirmed the plate’s past presence. Using advanced computer modeling, they analyzed oceanic rock formations, which they describe as the “relics of Pontus.”

Their findings provide new insights into the plate’s long and complex history, stretching back 160 million years. The most recent evidence suggests that it persisted in some form until about 20 million years ago.

A decade ago, researchers at Utrecht University proposed the idea that Pontus had once existed. Their theory was based on seismic signals—disturbances in earthquake waves that hinted at the presence of ancient, subducted plates deep within the Earth’s mantle.

However, direct geological evidence remained elusive. That changed with Van de Lagemaat’s recent study, which combined field research and laboratory analysis of rock samples to reconstruct Pontus’s history with unprecedented detail.

To better understand the scope and movement of the Pontus plate, Van de Lagemaat’s team examined geological structures across the region.

They focused on mountain belts in Japan, Borneo, the Philippines, New Guinea, and New Zealand, areas known to be part of one of Earth’s most geologically complex zones. Each of these locations contained fragments of ancient oceanic crust that helped piece together the plate’s story.

One of the most crucial discoveries came from northern Borneo. Initial analysis suggested these rocks were remnants of a known lost plate, but further investigation told a different story. Magnetic signatures within the rocks indicated they had originated much farther north than previously thought.

“We thought we were dealing with relics of a lost plate that we already knew about,” said Douwe van Hinsbergen, Van de Lagemaat’s PhD supervisor. “But our magnetic lab research on those rocks indicated that our finds were originally from much farther north and had to be remnants of a different, previously unknown plate.”

Additional evidence surfaced in Palawan, an island in the western Philippines, and the South China Sea. These discoveries suggest that the Pontus plate was once part of a unified tectonic system stretching from southern Japan to New Zealand. This vast network of interconnected plates shaped the western Pacific region for over 150 million years.

Understanding lost tectonic plates like Pontus is crucial for reconstructing Earth’s geological past and predicting future tectonic activity. Subduction zones not only recycle Earth’s crust but also drive mantle convection—the process that moves heat and material through the planet’s interior.

The discovery of Pontus provides a missing link in models of the western Pacific’s tectonic history, refining our knowledge of how plates interact and evolve.

Seismic imaging has played a critical role in this research. By analyzing how earthquake waves travel through the mantle, scientists can detect differences in material density. These variations reveal ancient plate fragments buried deep within the Earth, some of which date back as far as 300 million years. The technique helped researchers confirm that Pontus was once part of a vast subduction system dividing the paleo-Pacific Ocean.

Dr. Van de Lagemaat’s findings also validate a long-standing theory: that a massive subduction zone once existed along the western edge of the Pacific. This zone separated the well-documented eastern Pacific plates from the now-confirmed Pontus plate.

The research, published in Gondwana Research, offers a comprehensive look at how Earth’s tectonic system evolved over millions of years.

With this new understanding of Pontus, scientists are one step closer to unraveling the mysteries of Earth’s dynamic history. These discoveries remind us that the planet is constantly shifting beneath our feet, rewriting its own geological story with each passing millennia.

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