Africa’s Continental Split May Hold Clues To What’s Happening Deep Inside Earth

SOUTHAMPTON, England — Deep beneath East Africa, something extraordinary is happening 25 to 75 miles underground. Hot rock is flowing like thick syrup through the Earth’s interior, but scientists have found that the speed at which continents split apart at the surface is actually controlling how that molten material moves in the deep. This is the reverse of what researchers have believed for decades.

The study, published in Nature Geoscience, focuses on the Afar Triangle in East Africa, where three tectonic plates meet in a geological hot zone. Deep below Earth’s surface (25-75 miles), the Earth’s rocky mantle behaves like thick, flowing honey heated to over 2,000 degrees Fahrenheit.

Research team leader Emma Watts from the University of Southampton and her colleagues analyzed more than 130 volcanic rock samples from across the region where the Red Sea, Gulf of Aden, and East African rifts converge.

A Look Into Earth’s Violent Past

Afar represents one of the few places on Earth where scientists can study continental breakup in real time. Here, the African continent is literally splitting apart as three massive tectonic plates slowly drift away from each other. The Red Sea Rift spreads at about 0.57 inches per year, the Gulf of Aden moves roughly 0.61 inches annually, while the slower Main Ethiopian Rift creeps along at just 0.20 inches per year.

These might sound like tiny measurements, but over millions of years, they add up to ocean basins and mountain ranges. The process creates ideal conditions for studying how deep mantle material, the hot, rock-like substance that makes up most of Earth’s interior, moves and melts as it rises toward the surface.

Previous theories suggested that hot plumes of material rising from deep in the Earth’s mantle drove surface volcanism and continental splitting. But this new research suggests the surface processes actually influence the deep mantle flow patterns.

Watts and her international team specifically targeted volcanic samples less than 2.58 million years old from volcanoes that have been active within the last 11,700 years. This ensured they were studying the most recent volcanic activity that could be directly compared to current measurements of the region.

The researchers analyzed the chemical fingerprints of these rocks, focusing on radioactive elements like lead, neodymium, and strontium that can reveal the deep sources of the magma. They also incorporated seismic data showing how fast earthquake waves travel through the mantle at different depths. Slower waves indicate hotter, partially molten rock.

The researchers used advanced computer models to test five ideas about how hot rock rises from deep inside the Earth beneath the Afar region. They found the best explanation was one large pocket of rising molten rock that moves in different ways depending on how each rift above it is spreading.

Speed Matters in the Deep Earth

Chemical differences from deep within the Earth show up in repeating patterns across the different rifts, suggesting bursts of rising molten rock from the same deep source. But these bursts get squeezed closer together in areas where the rifts are spreading more slowly and the crust above is thicker.

This happens because fast-spreading rifts with thin crust create more room for the mantle material to flow, like water through a wide pipe. Slow-spreading rifts with thick crust create a bottleneck effect, compressing the flow patterns and changing how the deep Earth’s chemical variations show up at the surface.

The research involved analyzing rocks from previously unstudied volcanoes, roughly doubling the amount of high-quality chemical data available from the region. The team supplemented their own fieldwork with existing data and created detailed maps showing how chemical compositions vary across the landscape.

In regions where the Earth’s crust is thinner, like along the Red Sea rift, the volcanic rocks show less contamination from crustal materials and more direct signals from the deep mantle source.

The analysis showed that while some mixing with the Earth’s crust does happen, especially where the crust is thicker, it can’t explain the bigger picture. Instead, the patterns the team saw point to real differences in the deep molten rock itself and how it moves under each part of the rift system.

The study also found that the rising molten rock isn’t sitting right beneath the spot where the three rifts meet, like scientists used to think. Instead, it’s off-center and seems to be flowing more toward the faster-moving Red Sea rift.

A New View from the Deep

For decades, the prevailing view has been that deep mantle plumes drive surface volcanism and continental breakup, but the relationship seems to be more of a two-way street.

These forces will continue splitting Africa apart and eventually create a new ocean basin over time. The speed at which continents split apart, controlled by large-scale tectonic forces, apparently influences how material flows in the mantle more than 60 miles below. If mantle flow patterns are controlled by surface spreading rates, then geologists may be able to better predict where certain types of volcanic activity are most likely to occur.