Geologists have made the surprising discovery that large portions of Africa’s tectonic plate have disappeared, with one likely cause.
An international team of scientists led by the Dublin Institute for Advanced Studies (DIAS) has uncovered a geological mystery beneath Africa. In a paper published to Nature Communications, the team showed that large portions of the African tectonic plate – otherwise known as the lithosphere – have disappeared over the past 200m years.
Using seismic tomography data obtained from earthquakes across the globe, the team created 3D models of the lithosphere beneath Africa. It then used diamonds to get a glimpse into the structure of the lithosphere in the past.
“These ancient, thickest parts of the African continent had been stable since their formation over 2.5bn years ago. In view of this remarkable stability, their recent demise is a surprise,” said Prof Sergei Lebedev of DIAS.
“Diamonds played a key role in our discovery. Diamonds come from deep within the thickest tectonic plates on Earth. With them, they bring evidence of catastrophic destruction of some of these plates.”
Diamonds are brought to the surface by volcanic eruptions sourced from continental plates 150km deep within Earth. At such depths, diamonds are stable as, if they were any closer to the surface, the pressure would be too low and the carbon atoms would arrange themselves to form graphite.
Therefore, with the discovery of diamonds, it tells the team the tectonic plate from which they came was located between 200km and 300km beneath the Earth’s surface.
10 times larger than Tibetan Plateau
Dr Nicolas Celli, also of DIAS and lead author of the study, said: “To our surprise, seismic tomography revealed thin lithosphere in many locations in Africa, including South Africa, Angola and Tanzania, where it used to be thick only 30m to 200m years ago, according to diamonds.
“This implies that the plate in these locations got much thinner, by at least 10km, during the last 200m years. The volume of the missing tectonic plate material is as much as 100m cubic kilometres, over 10 times the volume of the Tibetan Plateau.”
In trying to explain the likely trigger for such a catastrophic thinning of the lithosphere, Lebedev said it was likely caused by the impact of hot upwellings from the planet’s core, known as mantle plumes. These plumes are thought to be responsible for enormous volcanic eruptions and even mass extinction events.
“As tectonic plates slide past each other and continents drift along the surface of the Earth, the convective mantle plumes rise from below and strike the bottom of the plates,” Lebedev said.
“Our new findings imply that the fate of each ancient core of a continent depends, to a large extent, on its luck in dodging the mantle plumes.”