A long-lost tectonic plate that once formed the basis of today’s South China Sea has been rediscovered 20 million years after it disappeared.

The plate is known only from a few rock fragments from the mountains of Borneo and the ghostly remains of its massive plate discovered deep in the Earth’s mantle. It was once a quarter the size of the Pacific Ocean. Scientists call it the “Pontic Plate” because when it existed, it was under the ocean known as the Pontic Ocean.

Van de Lagemaat and his colleagues first examined the Pacific Plate beneath the Pacific Ocean. Tectonic plates constantly move against each other, and oceanic plates have a denser crust than continental plates, so oceanic plates are pushed beneath continental plates and disappear in a process called subduction. However, sometimes the stones of the lost plate are involved in mountain formation processes. These remains may indicate the location and formation of ancient plates.

Researchers have been trying to find remnants of one of these ancient lost plates, known as the Phoenix plate, during fieldwork in Borneo. Van de Lagemaat says scientists can learn when and where rocks were formed by looking at their magnetic properties; The magnetic field surrounding the Earth “attaches” to rocks as they form, and this magnetic field varies with latitude.

But when researchers analyzed a stone found in Borneo, they discovered something strange.

“This latitude did not match the latitude we got from other plates that we already knew about,” Van de Lagemaat said.

To solve the mystery, he studied the geology of the region over the last 160 million years using computer models. Reconstruction of the plate showed that there was once a crack between Borneo and modern-day southern China, an ocean thought to be supported by another ancient plate called the Izanagi Plate that does not actually exist. Instead, Borneo’s rocks fit into this mysterious gap.

Researchers discovered that the area was actually occupied by a previously unknown plate; Van de Lagemaat and his team called this the Pontic Plate.

The reconstruction, published Sept. 29 in the journal Gondwana Research, shows that the Pontic Plate formed at least 160 million years ago, but is likely much older. (Rock samples collected in Borneo date back 135 million years.) It was once very large, but steadily shrank throughout its life, eventually being pushed beneath the Australian Plate in the south and China in the north, and vanishing 20 million years ago.

Research conducted by the same laboratory ten years ago also revealed a clue about the Pontic Plate. As a result of the study, images of the mantle, the middle layer of the Earth, where the sinking crust ends, were examined. Van de Lagemaat said a large layer of tree bark of unknown origin was revealed, but scientists could not determine where it came from. It is now clear that this crust is what is left of the Pontic Plate. Source