Earth is slowly peeling its continents from below, fueling ocean volcanoes

Researchers from the University of Southampton found that fragments of continents are gradually stripped away from below and drawn into the oceanic mantle -- the hot, mostly solid layer beneath the sea floor that slowly circulates. Once there, this continental material can power volcanic eruptions for tens of millions of years.

This discovery resolves a long-standing geological puzzle: why certain ocean islands located far from tectonic plate boundaries contain chemical signatures that look distinctly continental, even though they lie in the middle of vast oceans.

The study, published in Nature Geoscience, was conducted by an international team from the University of Southampton, GFZ Helmholtz Centre for Geosciences in Potsdam, the University of Potsdam, Queen's University (Canada), and Swansea University.

Ancient chemical clues deep within the mantle

Ocean islands such as Christmas Island in the northeast Indian Ocean often contain unusually high concentrations of certain "enriched" elements that typically come from continents. Scientists have compared this mixing process to the motion of a cake mixer folding in older, recycled ingredients from deep within the Earth.

For years, geologists assumed these enriched elements came from ocean sediments pulled into the mantle when tectonic plates sink, or from columns of rising hot rock known as mantle plumes.

However, those explanations have limits. Some volcanic regions lack evidence of recycled crust, while others seem too shallow and cool to be driven by deep mantle plumes.

"We've known for decades that parts of the mantle beneath the oceans look strangely contaminated, as if pieces of ancient continents somehow ended up in there," said Thomas Gernon, Professor of Earth Science at the University of Southampton and the study's lead author. "But we haven't been able to adequately explain how all that continental material got there."

Continents are peeling from below

The researchers propose a new mechanism: continents not only split apart at the surface but also peel away from below, and across far greater distances than scientists once believed possible.

To test this, the team built computer simulations that recreated how the mantle and continental crust behave when stretched by tectonic forces.

Their results show that when continents begin to break apart, powerful stresses deep within the Earth trigger a slow-moving "mantle wave." This rolling motion travels along the base of the continents at depths of 150 to 200 kilometers, disturbing and gradually stripping material from their deep roots.

The process happens at an incredibly slow rate -- roughly a millionth the speed of a snail. Over time, these detached fragments are carried sideways for more than 1,000 kilometers into the oceanic mantle, where they feed volcanic activity for tens of millions of years.

Study co-author Professor Sascha Brune of GFZ in Potsdam explained, "We found that the mantle is still feeling the effects of continental breakup long after the continents themselves have separated. The system doesn't switch off when a new ocean basin forms -- the mantle keeps moving, reorganizing, and transporting enriched material far from where it originated."

Clues from the Indian Ocean

To support their model, the team analyzed chemical and geological data from regions such as the Indian Ocean Seamount Province -- a chain of volcanic formations that appeared after the breakup of the supercontinent Gondwana over 100 million years ago.

Their findings show that soon after Gondwana split apart, a pulse of magma unusually rich in continental material erupted to the surface. Over time, this chemical signature gradually faded as the flow of material from beneath the continents diminished. Notably, this happened without the presence of a deep mantle plume, challenging long-held assumptions about the source of such volcanism.

Professor Gernon added: "We're not ruling out mantle plumes, but this discovery points to a completely new mechanism that also shapes the composition of the Earth's mantle. Mantle waves can carry blobs of continental material far into the oceanic mantle, leaving behind a chemical signature that endures long after the continents have broken apart."

The research also builds on the team's earlier work showing that these slow, rolling mantle waves can have dramatic effects deep inside continents. Their previous studies suggest that such waves may help trigger diamond eruptions and even reshape landscapes thousands of kilometers away from tectonic boundaries.