The vertical movement of the mantle is one of the driving forces that brings about large-scale geological changes to the surface of our planet. These mantle upwellings, sometimes referred to as mantle plumes, are hypothesized to play a role in some major geological shifts such as continental drifting. A similar, subtle yet significant phenomenon has been found to be currently taking place beneath the African continent.
A new study published in the journal Nature Geoscience has revealed that the rhythmic surges of molten rocks, pulsing upward like a "heartbeat," are ripping the continent apart, likely paving the way for a new ocean. This asymmetric and chemically heterogeneous upwelling, influenced by tectonic movement, is concentrated below the Afar region in Ethiopia.
The Afar is a geologically intriguing place where the Arabian, Nubian, and Somalian tectonic plates intersect. Here, the rifting of these three tectonically active plates has occurred at different rates. Over millions of years, the heartbeat-like pulses will ultimately thin and weaken the continent, stretching it like soft plasticine, until it ruptures. This rupture will mark the birth of a nascent ocean.
“We found that the mantle beneath Afar is not uniform or stationary – it pulses, and these pulses carry distinct chemical signatures,” said the lead author of the study, Dr Emma Watts. “These ascending pulses of partially molten mantle are channelled by the rifting plates above. That’s important for how we think about the interaction between Earth’s interior and its surface.”
For years, geologists have hinted at a hot mantle plume lurking underneath, driving the extension of Africa. Yet, the precise driver and behavior of upwelling remained largely unexplained.
To learn more about the plume, Earth scientists at the University of Southampton sampled over 130 volcanic rocks from Afar and the Main Ethiopian Rift. Using the mathematical and computational models, researchers were able to gather insights into the Earth’s depth and composition of materials under the Afar surface.
The team found a single, spatial upwelling under the three rifts, but with a different chemical composition. These upwellings tend to repeat in a specific rhythm, acting like geological barcodes. Scientists also revealed that these plumes, originating between the depths of 1,000 and 2,800 km (621 and 1,740 miles), contain varying isotopes, possibly from primordial mantle material, which makes the region slightly hotter than the surrounding mantle.
The varying chemical striping suggests that the upwelling behaves differently with the thickness of the lithosphere (the Earth's crust and the upper mantle); the thicker the plate, the slower the molten pulse.
“The work shows that deep mantle upwellings can flow beneath the base of tectonic plates and help to focus volcanic activity to where the tectonic plate is thinnest. Follow-on research includes understanding how and at what rate mantle flow occurs beneath plates,” says the associate author, Dr. Derek Keir.
The study has been published in Nature Geoscience.
Source: University of Southampton