Around 120 million years ago, Earth experienced one of the most massive volcanic events in its history—the formation of the Ontong Java Plateau in the Pacific Ocean. This is not merely an enormous volcanic structure larger than Greenland, but an event that fundamentally reconfigured the oceanic crust. Scientists from Okayama University of Science in Japan have concluded that magma did not simply erupt onto the surface; it also penetrated deep into the lithosphere, altering its structure and chemical composition. Their findings were published in Geophysical Research Letters.

The Ontong Java Plateau: A Giant Beneath the Sea

The Ontong Java Plateau is the largest volcanic formation on the planet, entirely submerged in the western Pacific Ocean. Its area exceeds that of Greenland, making it a true geological colossus. According to current understanding, it formed as a result of the rise of a massive mantle plume—a column of extremely hot material ascending from deep within the Earth. This event not only created the plateau but likely also influenced the global climate of the time, triggering large-scale changes in the atmosphere and oceans.

Until recently, researchers focused mainly on the surface expressions of the eruption. However, the new study shows that the processes extended much deeper, affecting the very foundation of the oceanic lithosphere.

Ocean-Floor Seismometers Reveal Anomalies

To investigate further, the researchers deployed ocean-bottom seismometers—special instruments placed on the seafloor to record earthquakes and other vibrations. These devices allowed the team to analyze how high-frequency seismic waves travel beneath the plateau.

The data revealed an unusual anomaly: one type of seismic wave weakened rapidly and moved more slowly than expected for typical oceanic crust. This did not fit standard models, prompting the team to conduct computer simulations to explain the phenomenon.

Dikes and the Reshaping of the Lithosphere

The models showed that the oceanic plate beneath the plateau has a complex, heterogeneous structure. Layers of sedimentary rock and lava are cut through by numerous vertical dikes—solidified channels through which magma once rose. This indicates that molten material did not simply flow out at the surface but actively intruded into the plate, making it more porous and altering its chemical composition.

The study’s authors emphasize that such processes demonstrate how deep-sourced magma can profoundly transform the lithosphere during the largest volcanic events in Earth’s history. The discovery provides new insight into the evolution of tectonic plates and the role of mantle plumes in shaping the planet’s geological history.

In Brief

Researchers from Okayama University of Science found that the formation of the Ontong Java Plateau 120 million years ago not only involved massive lava outpourings but also deeply restructured the oceanic crust. Magma intruded into the lithosphere through vertical dikes, changing its structure and composition. The anomalies were identified using ocean-bottom seismometers and computer modeling, underscoring the powerful role of mantle plumes in driving global geological change.