British researchers have made a revolutionary discovery, uncovering the mechanism by which fragments of continents separate and move beneath the oceans, sustaining volcanic activity for millions of years. The work was published in the journal Nature Geoscience.
Scientists have long wondered why volcanic islands located far from tectonic plate boundaries contain chemical elements characteristic of continents. For example, where did the "continental" traces in the lava of Christmas Island in the Indian Ocean come from?
A team of scientists from the University of Southampton, along with colleagues from Germany, Canada, and Wales, found an answer that changes our understanding of the inner workings of our planet.
The study mentions that for a long time, scientists noticed strange contaminations in the mantle beneath the oceans, as if pieces of ancient continents had ended up there. However, they could not explain how this continental material got there.
It turns out that when continents begin to crack under tectonic forces, a unique mechanism—"mantle wave"—is activated deep within the Earth. This slow rotational movement spreads across the base of the continents at a depth of 150-200 km.
Imagine a giant roller that slowly moves beneath the continent, gradually scraping material from its deep roots, just like a scraper removes a layer of paint.
Although the process occurs extremely slowly—about a million times slower than a snail's movement—over millions of years, fragments of continental rock move more than 1000 km toward the ocean and enter the mantle—a hot layer beneath the ocean floor.
To test their hypothesis, the research team conducted computer simulations of the behavior of the Earth's crust and mantle, and then compared the results with real geological data from the Indian Ocean.
The analysis of the Indo-Oceanic underwater province, a chain of volcanic formations that arose after the breakup of the supercontinent Gondwana more than 100 million years ago, proved particularly revealing.
It was found that shortly after the breakup of Gondwana, magma rich in continental material erupted to the surface, although over time the concentration of these elements decreased as the flow of material from beneath the former continents was exhausted.
Interestingly, the mantle continues to experience the effects of continental breakup long after their separation. The system does not cease its operation with the formation of a new oceanic basin—the mantle continues to move and carry enriched material far from its origin.
It was previously believed that "continental" elements in oceanic volcanoes could enter through two main pathways: either along with oceanic sediments during the subduction of tectonic plates or from deep mantle plumes—upward flows of hot rock from the Earth's interior.
However, these explanations did not always hold. In some volcanic regions, there are no signs of recycled crust, while others are too cold and shallow for mantle plumes.
The new discovery offers a third mechanism that can operate independently of the previous ones. In particular, in the case of the Indo-Oceanic province, volcanism occurred without the involvement of a deep mantle plume.
The study emphasizes that this discovery points to a new mechanism for forming the composition of the Earth's mantle. Mantle waves can carry continental material deep into the oceanic mantle, leaving a chemical trace that persists long after the continents have been destroyed.
The work demonstrates that our planet is much more dynamic than previously thought. The processes in its depths are interconnected by complex feedback loops and continue to influence the surface for tens of millions of years after the initial event.
