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Sophisticated chemical analysis of volcanic gases from Kenya has provided the first evidence that a vast mass of deep Earth material lies beneath East Africa.

An international team of scientists led by Professor Fin Stuart from the University of Glasgow, working in partnership with the Kenya Geothermal Development Company, has discovered surprising results in a new study of gases from the Menengai geothermal field in central Kenya.

Their findings could help resolve a long-standing debate about how the East African Rift System formed.

The rift valleys of East Africa are some of the largest and most spectacular topographic features on Earth. They extend for 3,500 km through Ethiopia, Kenya, Uganda and Malawi, and host extensive volcanic fields. The rifts are the manifestation of the African tectonic plate being split apart, driven by forces deep in Earth's interior.

Scientists are uncertain whether the volcanism and rifting are due to shallow processes or whether it is driven by upwelling hot material from deep in Earth, probably from the boundary between the core and mantle.

In a new paper in the journal Geophysical Research Letters, the team from the Scottish Universities Environmental Research Center (SUERC) concludes that the hot mantle beneath Kenya originates from very deep in Earth. Their findings are based on high-precision mass spectrometry analysis of high-temperature gases from a geothermal field in the Kenya Rift Valley.

The team's key observation is that the geothermal gases are volcanic in origin, and the isotopes of the noble gas neon in the gases originate in the deep mantle, likely from the boundary between the core and the mantle. Their analysis shows for the first time that the gas composition is identical to gases in volcanic rocks from the Red Sea to the north and in Malawi to the south.

This common "fingerprint" of gases from across a large distance suggests that the same type of hot deep mantle rock is present beneath the whole region, driving volcanic activity and pushing apart the tectonic plates.

The discovery is the first clear geochemical evidence in support of the theory that a single "superplume" of deep mantle has been produced at a large mass of anomalous rock at the core-mantle boundary beneath southern Africa.

The team notes that the gases are chemically indistinguishable from gases present in volcanic rocks from Hawaii that are proposed to originate from a similar anomalous region beneath the Pacific Ocean.

Professor Stuart said, "We have long been interested in how the deep Earth rises to the surface, how much is transported, and just what role it plays in forming the large-scale topography of Earth's surface. Our research suggests that a giant hot blob of rock from the core-mantle boundary is present beneath East Africa. It is driving the plates apart and propping up the African continent so it is hundreds of meters higher than normal."

Biying Chen of the University of Edinburgh and SUERC, the paper's corresponding author, said, "These gases from our geothermal wells have provided valuable new insight into Earth's deep interior, helping us better understand not only the geological forces shaping East Africa but also the fundamental processes which drive the formation of our planet's surface over millions of years."