The Earth’s largest continental rift, the East African Rift (EAR), has long been a mystery to geologists. But a new study combining computer models with GPS satellite data has revealed interesting results. Crustal deformation in this region is not only perpendicular to the movement of tectonic plates, but also parallel to it. Three-dimensional models developed by the authors of the study indicate that this additional parallel deformation is the result of the African superplume, a massive rise of the hot mantle from deep within our planet, carrying heat to the surface.
What are rifts and how do they arise?
Rifts are the result of tectonic plates moving away from each other, causing the lithosphere (crust and upper mantle) to stretch and break apart. This leads to deformations at the Earth’s surface, usually perpendicular to the movement of the plates.
EAR: an enigma for geologists
The EAR extends about 6,400 kilometers (almost 4,000 miles), and it is thought to divide Africa into two parts over millions of years. As the lithosphere stretches and becomes thinner, we will see more earthquakes and rock failures throughout the region.
The results of a new study
Three-dimensional models developed by the authors of the new study indicate that additional parallel deformation, which is not characteristic of rifts, is the result of the African superplume. This upwelling of partially molten rock extends from southwest to northeast Africa, becoming shallower along the way and forming a mantle flow beneath it.
The African superplume and geological movements
It looks like the mantle flow may be “causing an anomalous northward deformation parallel to the rift,” says geophysicist Tahiri Rajaonarison of the New Mexico Institute of Technology. The same African superplume is probably responsible for some seismic anisotropy – the alignment of rocks in a particular direction in response to geologic forces in the mantle – occurring beneath the EAR, as researchers have previously noted.
How does the lithosphere behave on different timescales?
The research team is comparing different deformations that can occur simultaneously, as with the Silly Putty. “If you hit Silly Putty with a hammer, it can crack and break,” says geophysicist D. Sarah Stamps of the Virginia Institute of Technology. “But if you slowly stretch it, the silly putty will stretch. So the Earth’s lithosphere behaves differently on different timescales.”
Predicting geological movements is a difficult task
But predicting such large-scale geological movements is an incredibly difficult task. The research team says the deformations are consistent with the African superplume model. But more research is needed to make more accurate predictions.