New scientific research has revealed that the oceanic lithospheric plate beneath the Ontong Java Plateau – the largest oceanic plate on the planet – underwent extensive physicochemical changes as a result of extreme volcanic activity during its formation. The findings are published in the prestigious journal Geophysical Research Letters and provide new insights into the processes that shape Earth's oceanic plates.
The Ontong Java Plateau is located in the Pacific Ocean and was formed about 110–120 million years ago, after massive underwater volcanic eruptions, considered the largest in the geological history of the planet. This gigantic volcanic activity has been linked to dramatic changes in the global environment and, according to some hypotheses, even to episodes of mass extinction of species. The study was carried out by an international team of researchers, led by lecturer Azusa Shito of Okayama University of Science, with the participation of scientists from the Tokyo Institute of Science and Hiroshima University. They analyzed high-frequency seismic waves, known as Po and So waves, which are recorded by seismographs located on the ocean floor and on oceanic islands.
These waves travel within oceanic plates and serve as natural “X-rays” to understand their internal structure. The analysis revealed an unusual pattern: while Po waves propagated normally beneath the plate, So waves were significantly attenuated. Such a phenomenon is not observed in typical oceanic plates and points to a much more complex internal structure.
According to models developed by the researchers, the oceanic plate beneath Ontong Java consists of horizontal layers interrupted by vertical systems of magmatic intrusions, known as “dikes.” At the same time, the slower propagation speed of seismic waves suggests that the plate material has been chemically modified at depth. Scientists estimate that magma from a thermochemical mantle plume – a powerful stream of material rising from the depths of the Earth’s mantle – has penetrated the existing oceanic plate. This process not only created the plateau’s giant volcanic masses, but also chemically “revitalized” the plate, changing its composition in the long term. The study’s findings reinforce the idea that oceanic plates are not passive and unchanging structures, but can be profoundly transformed by extreme volcanic episodes. According to the researchers, this new model helps to provide a more complete understanding of the processes that shape the Earth's crust and the crucial role that volcanic activity has played in the planet's evolution.
