East African rift system slowly separates, Madagascar splitting into pieces

The African continent slowly separates into several large and small tectonic blocks along the diverging Rift system of East Africa, continuing to Madagascar – the long island just off the coast of South Africa – Is – which itself will also separate into smaller islands.

These developments will redefine Africa and the Indian Ocean. The discovery comes in a new study by D. Sarah Stamps of the Department of Geosciences for the journal Geology. The rupture is the continuation of the breakup of the supercontinent Pangea about 200 million years ago.

Rest assured, however, that this won’t happen anytime soon.

“The current break rate is millimeters per year, so it will be millions of years before new oceans start to form,” said Stamps, an assistant professor at the Virginia Tech College of Science. “The rate of expansion is the fastest in the north, so we’ll first see new oceans forming there.

Tahiry Rajaonarison, PhD student in geosciences, installs a GPS instrument in northern Madagascar in this 2016 photograph. Behind Tahir is the Indian Ocean and a rocky island. Photo credit: Rina Andrianasolo.

“Most of the previous studies have suggested that the extension is localized in narrow areas around the microplates that move independently of the large surrounding tectonic plates,” Stamps said. New GPS dataset of highly precise surface movements in East Africa, Madagascar and several Indian Ocean islands reveals that the disruption process is more complex and distributed than previously thought, according to the study, completed by Stamps with researchers from the University of Nevada-Reno, the University of Beira Interior in Portugal, and the Institute and Observatory of Geophysics of Antananarivo at the University of Antananarivo in Madagascar itself .

In one region, the researchers found that extension is spread over a large area. The distributed extension region is approximately 600 kilometers (372 miles) wide, stretching from East Africa to entire parts of Madagascar. Specifically, Madagascar actively breaks with southern Madagascar moving with the Lwandle microplate – a small tectonic block – and a piece of central Madagascar moves with the Somali plate. The rest of the island is seen to be deforming non-rigidly, Stamps added.

The geoscience doctorate also worked on paper. student Tahiry Rajaonarison, who was previously a master’s student at the University of Antananarivo in Madagascar. He helped Stamps in 2012 collect the GPS data that was used in this study. He joined Virginia Tech in 2015 and returned to Madagascar later to collect more data as a National Geographic Society grant manager. “Leading a team responsible for collecting GPS data in Madagascar in the summer of 2017 was an incredible field experience,” said Rajaonarison.

The team used new surface motion data and additional geological data to test various tectonic block configurations in the region using computer models. Through a comprehensive suite of statistical tests, the researchers set new limits for the Lwandle Microplate and Somali Plate. This approach made it possible to test whether the surface motion data is consistent with the rigid plate motion.

“Accurately defining plate boundaries and assessing whether continents diverge along narrow strain zones or across wide diffuse strain zones is crucial to unraveling the nature of continental breakage,” Stamps said. “In this work, we have redefined the way the world’s largest continental rift stretches using a new GPS speed solution.

The discovery of the large deformation zone helps geoscientists understand recent and ongoing seismic and volcanic activity in the Comoros Islands, located in the Indian Ocean between East Africa and Madagascar. The study also provides a framework for future studies of global plate motions and investigations of the driving forces of plate tectonics for Stamps and his team.