Geologists Baffled After Locating Portion of Earth That Disappeared 20 Million Years Ago

Researchers have discovered an ancient tectonic plate that disappeared 20 million years ago, says a study.

Suzanna van de Lagemaat, a doctoral candidate of Geology from Utrecht University, Netherlands, has managed to reconstruct a tectonic plate that at one point in time used to be one-quarter the size of the Pacific Ocean, Science Daily reported. Lagemaat recorded her findings through the reconstruction in a study published in Gondwana research.

Throughout Earth's history, many oceanic plates have disappeared under continental plates, on account of being more dense, Live Science reported. Sometimes rocks from these lost oceanic plates get involved in mountain-building events.

Experts focus on the magnetic properties of these rocks to get more information about the origin and destruction of the ancient tectonic plates.

Initially, Lagemaat and her colleagues approached the fieldwork to find the remnants of the Phoenix plates, another collection of lost plates, Live Science reported. 

The magnetic properties of the rocks indicate the time when they were formed in the earth's history. The magnetic field surrounding the Earth gets locked into the rocks when they are formed, Lagemaat explained. 

The rocks, the team found from Borneo did not match the magnetic properties of the available samples from the Phoenix plate, Live Science reported. "This latitude didn't fit with the latitude we got from the other plates that we already knew about," Lagematt shared. 

"We thought we were dealing with relicts of a lost plate that we already knew about," Van de Lagemaat said, Science Alert reported. "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," she added.

Lagemaat used computer models to investigate Borneo's geology over the last 160 million years, Live Science reported. She noted through the reconstructed models that an ocean which was previously considered to be under another ancient plate called the Izanagi plate was not present in that position, between South China and Borneo.

That gap was filled by the rocks that the team found from Borneo. The team concluded that the spot was occupied by the Pontus oceanic plate. The remnants of Pontus along with northern Borneo, can be found on Palawan, an island in the Western Philippines, and in the South China Sea, Science Daily reported.

The Pontus plate was formed at least 160 million years ago, according to the study. Initially, it was enormous but continued to shrink steadily over its lifespan. Eventually, it got pushed under the Australian plate to the south and China to the north, disappearing 20 million years ago.

Speculations about the plate's existence were raised by Lagemaat's university a decade ago based on the old tectonic fragments found deep in the Earth’s mantle, Science Daily reported. Researchers then also tried to understand more about the plate, but could not verify many of their theories.

"11 years ago, we thought that the remnants of Pontus might lie in northern Japan, but we'd since refuted that theory," explains Douwe van Hinsbergen, Van de Lagemaat's PhD supervisor, Science Daily reported.

"It was only after Suzanna had systematically reconstructed half of the 'Ring of Fire' mountain belts from Japan, through New Guinea, to New Zealand that the proposed Pontus plate revealed itself, and it included the rocks we studied on Borneo," said van Hinsbergen.

Lagemaat explored the mountain belts of Japan, Borneo, the Philippines, New Guinea, and New Zealand to reconstruct the lost plate, Science Daily reported. The findings of her field research made Lagemaat conclude that the oceanic remnants present in northern Borneo were once a part of the long-suspected plate, Pontus.

The name, 'Pontus' was chosen by the experts because when it was intact, the plate sat under the Pontus Ocean, Live Science reported. "It's surprising to find remnants of a plate that we just didn't know about at all," Lagemaat told the outlet.