Researchers from the University of Southampton (UK), together with colleagues from Germany, Canada and Wales, have proposed a new explanation for how volcanoes appear under the oceans far from the boundaries of tectonic plates. Their work, published in Nature Geoscience, shows:continents not only spread out on the surface, but also gradually “peel off” from below, sending their deep fragments into the oceanic mantle.

The mystery of volcanoes in the middle of the oceans

Many islands, including Christmas Island in the Indian Ocean, contain rocks rich in elements found in continental crust. This has long puzzled geologists:How did “pieces of continents” end up in the center of the oceans, far from the usual plate collision zones?

Previously, it was assumed that such enriched elements rise from the depths along with mantle plumes – hot flows of molten rock. Another hypothesis associated them with material recycled during the subsidence of oceanic plates. But none of these versions fully explained the observed chemical anomalies.

“We’ve known for decades that areas of the mantle beneath the oceans look strangely polluted, as if parts of ancient continents had somehow ended up there. But until now, no one has been able to show conclusively how this material gets there,” says geosciences professor Thomas Gernon, who led the study.

How the Earth sheds its “crust” from below

Scientists have modeled the process that occurs when continents move apart. Deep tectonic forces create a wave of instability in the lower mantle—a sort of “mantle wave”—that moves slowly along the base of the continents.At a depth of about 150–200 kilometers, it weakens their roots, as if cutting them from below.

This process is incredibly slow – only a millionth the speed of a snail. But over millions of years, it is capable of separating significant masses of rocks, which then move towards the oceanic mantle.These fragments become fuel for volcanoes, whose activity can continue for tens of millions of years after the continents break up.

Professor Sascha Bruhn from the Helmholtz Center for Geological Sciences (GFZ, Potsdam) notes:

“We found that the mantle continues to feel the effects of continental breakup for a long time. Even when a new ocean basin is formed, the system does not stop – it continues to move, carrying enriched material further and further from the starting point.”

Traces of ancient continents in the oceans

To test the hypothesis, the team examined geochemical data from the Indian Ocean—specifically, from an area of ​​seamounts formed after the breakup of the supercontinent Gondwanaland than 100 million years ago. The analysis showed:shortly after the breakup of the continent, a burst of unusually enriched magma actually appeared in the mantle.Over time, the chemical fingerprint began to weaken, indicating a gradual depletion of the flow of continental material.

It is curious that the process occurred without the participation of a mantle plume – a hot column of matter, which was previously considered an obligatory source of such activity.

“We don’t reject the existence of plumes, but now we have another, completely new mechanism that helps us understand how the chemical composition of the mantle is formed. Mantle waves can transport clots of continental material thousands of kilometers, leaving behind a long-lived chemical trace,” explains Professor Gernon.

New understanding of Earth dynamics

This discovery not only explains the origin of isolated oceanic volcanoes, but also changes the understanding of the deep dynamics of the planet. Previous studies by the same group have shown that such waves in the mantle can even cause eruptions of diamonds and affect the topography of continents thousands of kilometers from tectonic boundaries. It turns out that the Earth is much “alive” in its depths than it seemed before: it slowly sheds the layers from below, like an ancient tree that renews its bark.