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Long-lost mega-plate Pontus resurfaces after 160 million years

No one thought we would see the Pontus after 160 million years. But in a remarkable discovery, scientists have detected the existence of this mega-plate in the west Pacific Ocean.

The Pontus plate

The resurfacing of the Pontus plate is the latest discovery in the world of plate tectonics. It is believed that the massive tectonic plate was once about 15 million square miles in size, which equates to approximately one quarter of the Pacific Ocean. 

However, Pontus has been gradually subducted beneath the earth over the last millions of years. Scientists believe this gravitational force came from a neighboring plate.

Relics of Pontus 

Pontus can be traced back as far as 160 million years, and even more recently to around 20 million years back. By that point, its size would have been greatly reduced.

Suzanna Van de Lagemaat, a geologist at Utrecht University, led the study uncovering Pontus. She and her team leveraged the power of computer modeling to analyze oceanic rocks, which they call the “relics of Pontus.”  

The findings from the analysis shed more light on the plate and its complex geological history.

The science behind the discovery

Previously, Van de Lagemaat and other scientists at Utrecht University had predicted the existence of the Pontus about a decade ago. The prediction came after they discovered fragments of old tectonic plates deep in the Earth’s mantle.

In the current study, Van de Lagemaat reconstructed the lost plates by combining field research with extensive investigations of Japan, Borneo, the Philippines, New Guinea, and New Zealand Mountain belts. These areas were believed to be the “most complicated plate tectonic region.”

“The Philippines is located at a complex junction of different plate systems. The region almost entirely consists of oceanic crust, but some pieces are raised above sea level and show rocks of very different ages,” said Van de Lagemaat.

The reconstruction process

Van de Lagemaat and her team started by reconstructing the movements of the current plates in the region between Japan and New Zealand. 

This provided an idea about the size of the plates that disappeared in today’s western Pacific region.

Unknown plate

The researchers also encountered relics of a lost plate during their investigation of northern Borneo. But these were remnants of a different, unknown plate.

“We also conducted fieldwork in northern Borneo, where we found the most important piece of the puzzle,” said Douwe van Hinsbergen, Van de Lagemaat’s PhD supervisor.

“We thought we were dealing with relics of a lost plate that we already knew about. 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.”

Coherent plate tectonic system 

In addition to northern Borneo, Pontus plate relics were found in Palawan, an island in the Western Philippines, and the South China Sea. 

The research also indicates that a single coherent plate tectonic system extends from southern Japan to New Zealand. Scientists believe this system may have existed for at least 150 million years.

Breaking new boundaries

Previous assumptions about the existence of the Pontus plate were grounded in the traces left behind by subducted plates. 

These traces exist in zones of unusual temperatures and compositions within the Earth’s mantle, but they become evident when seismographs record signals from earthquakes.

The movement of the seismic waves through the zones of anomaly usually disrupts the signal. Geologists then trace these disruptions to an unusual event in the mantle, which could be fragments of tectonic plates.

This innovative technique means scientists can look as far back as 300 million years into the Earth’s past, considering the older plate fragments have depleted the boundary between the Earth’s core and mantle.

With Van de Lagemaat’s new discovery, we have confirmed a hypothesis from about 11 years ago that suggested that a large subduction zone passed through the western paleo-Pacific Ocean. This separated the known eastern Pacific plates from the hypothetical western Pontus plate.

The study is published in the journal Gondwana Research.

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