Unusual gases rising from geothermal springs within the Kafue Rift of Zambia suggest a deep fracture in Earth’s crust could mark the early stages of a new tectonic boundary.
Location map of the extensional zone within the Central African Plateau of Zambia. The Kafue Rift is connected to the Luano and Luangwa rifts to the NE, and the Western branch of the EARS at the Rukwa rift (RRB) and Rungwe Volcanic Province (RVP). Image credit: Karolytė et al., doi: 10.3389/feart.2026.1799564.
“The hot springs along the Kafue Rift of Zambia have helium isotope signatures which indicate that the springs have a direct connection with the Earth’s mantle, which lies between 40 and 160 km below the Earth’s surface,” said University of Oxford’s Professor Mike Daly.
“This fluid connection is evidence that the fault boundary of the Kafue Rift is active and therefore the Southwest African Rift Zone is too — and may be an early indication of the break-up of sub-Saharan Africa.”
The Kafue Rift is part of a 2,500-km-long zone of rifts that runs from Tanzania to Namibia and may reach the mid-Atlantic ridge.
The researchers were drawn to the region by its distinctive topography, widespread geothermal anomalies and numerous hot springs — all potential signs of a previously unrecognized rift system.
But to confirm the existence of a new rift, they needed evidence that it had penetrated the Earth’s crust, allowing fluids from the underlying mantle to rise to the surface.
“A rift is a large break in the Earth’s crust that creates subsidence and associated elastic uplift,” Professor Daly said.
“A rift may become a plate boundary, but commonly a rift’s activity ceases before the point of lithospheric break-up and plate boundary formation.”
The scientists visited eight geothermal wells and springs across Zambia: six in the suspected rift zone, and two outside it.
They took samples of gas from freely bubbling water, and analyzed these in the laboratory to identify the isotopes of each element present.
So by testing the isotopes present in the gas, they could detect the presence of gas derived from mantle fluids at the surface.
They compared these to readings taken from the East African Rift System, an ancient, well-established rift.
They found that the gas from the Kafue Rift, but not the gas from the springs outside the rift, contained a ratio of helium isotopes comparable to samples taken from the East African Rift System.
The samples also contained levels of carbon dioxide consistent with gases originating from mantle-derived fluids.
Helium isotopes provide a signal of early-stage rifting: using the East African Rift System as a model, scientists predict that with time, carbon dioxide will become more prominent as volcanic centers develop.
“Many of the features of the Great Rift Valley of Kenya offer compelling reasons why East Africa should ultimately become a line of major continental break-up,” Professor Daly said.
“But the rate of rifting of the East African Rift System is slow.”
“On almost all sides of Africa there are mid-ocean ridges tending to inhibit east-west or north-south extension, so break-up and spreading does seem to struggle to establish itself.”
“The Southwestern African Rift System could be an alternative. It has the required rift-related features, and regional basement fabrics — inherent weaknesses in the crust — favorably aligned to the surrounding mid-ocean ridges and continental geomorphology.”
“This relationship may offer a much lower strength threshold for continental break-up.”
“However, this study is based on helium analyses from one general area in the Southwest African Rift System, which is thousands of kilometers long,” Professor Daly said.
“This early study is being followed by more extensive studies, the next step of which will be completed this year.”
The study was published today in the journal Frontiers in Earth Science.
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Rūta Karolytė et al. 2026. The Southwestern Rift of Africa: isotopic evidence of early-stage continental rifting. Front. Earth Sci 14; doi: 10.3389/feart.2026.1799564