Earth scientists led by the University of Southampton have introduced a new mechanism to explain a long-standing geological puzzle.
The mystery was the presence of continental chemical materials in volcanic islands situated far out in the oceans.
According to the new study, a phenomenon known as continental peeling is likely the cause. It demonstrates that continents are being slowly stripped away from beneath, far from their tectonic boundaries.
Long-standing mystery
For decades, geologists have been puzzled by ocean islands like Christmas Island in the northeast Indian Ocean. These islands exhibit high levels of “enriched” elements — materials most often found in continents.
Earlier hypotheses for the continental material found in ocean islands centered on two main sources: ocean sediments recycled at plate boundaries or hot rock columns known as deep mantle plumes.
However, these theories failed to account for all observations adequately.
For instance, some volcanic regions exhibit little evidence of crustal recycling, while others are too cool and shallow 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, lead author. “But we haven’t been able to adequately explain how all that continental material got there.”
Mantle waves strip continental roots
The research puts forward an entirely new explanation.
Continents don’t just rift apart at the surface; they also peel away from below at their roots, which are 150 to 200 km deep.
As continents are stretched by tectonic forces, a slow-moving “mantle wave” sweeps along the base of the continent. This wave gradually strips slivers of rock from the deep continental base.
These continental fragments are then swept sideways into the oceanic mantle, sometimes travelling over 1,000 km.
Once in the oceanic mantle, this continental material contaminates the surrounding rock, providing fuel for volcanic activity that can endure for tens of millions of years in unexpected locations.
The mantle system remains active long after continents have separated, continuing to transport this enriched material far from its origin.
Ancient breakup simulation
To validate their simulations, the international team, which included researchers from the GFZ Helmholtz Centre for Geosciences and Queen’s University, Canada, analyzed geochemical data from the Indian Ocean Seamount Province.
It is a chain of volcanic features formed after the supercontinent Gondwana split over 100 million years ago.
“We found that the mantle is still feeling the effects of continental breakup long after the continents themselves have separated,” said Professor Sascha Brune, Study co-author from GFZ in Potsdam.
Their findings revealed a sudden eruption of magma with unusual enrichment, which occurred soon after the breakup of Gondwana. As the flow of peeled continental material lessened, this chemical signal progressively faded over a period spanning tens of millions of years.
Notably, this phenomenon occurred without a deep mantle plume, contrary to what geologists had previously assumed was necessary to create such features.
Professor Gernon notes that while the discovery doesn’t rule out mantle plumes, it “points to a completely new mechanism that also shapes the composition of the Earth’s mantle,” explaining how continents influence the deep ocean long after their initial separation.
The scientists conclude that continental breakup is a domino effect that initiates long-lived disturbances deep within the Earth, linking the fate of continental roots to unexpected geological activity worldwide.
The study was published in the journal Nature Geoscience on November 11.