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Ethiopian Ocean of The Future

09.06.2005

Research at the University of Leicester Department of Geology is confirming how a plume of hot mantle rock rising beneath Africa is splitting the continental crust apart and driving a plate tectonic sequence that could eventually form a new ocean in Ethiopia.

The extending East African Rift is a 3,000 kilometre crack in the Earth’s surface, stretching from Malawi in the south, through Tanzania, Kenya and Ethiopia, connecting with the Red Sea and the Gulf of Aden.

The character of the Rift changes from a faulted rift valley in Kenya, becoming more like a mid-ocean ridge in the northern Afar Depression, where magma rises to create the floor of an embryonic ocean.

Ethiopia lies in the transitional stage between the two, and studying the geological processes, structure and history of the magmatic Ethiopian Rift provides vital information about how a new ocean is formed.

Project EAGLE (the Ethiopia Afar Geoscientific Lithospheric Experiment) is a major earth science project in Africa looking at this process. Professor Peter Maguire, of the University of Leicester Department of Geology, is one of the leaders of this project, which is a collaboration between the Universities of Leicester, Leeds and Royal Holloway, London, as well as the University of Texas (El Paso) and Stanford, California, together with the University of Addis Ababa, Ethiopia.

The project, funded by the Natural Environment Research Council, aims to see deep into the Earth by using large seismic arrays to record natural earth tremors and vibrations from explosive charges detonated in boreholes. In addition, precise measurements of the Earth’s gravity field help to produce a 2D image of the Rift structure to a depth of almost 100 km.

Dave Cornwell, a geophysics PhD student working with Professor Maguire said:

“The Ethiopian Rift is where it’s all happening in one place – you have volcanoes, earthquakes, classic rift valley faults and complex geology. It’s one of a few places in the world where we can examine how geological processes combine to break up a continent.”

His research has found that the central Ethiopian rift structure is characterised by near-surface intrusions up to 20 km wide, consisting of dense igneous rock that originated in the upper mantle (at a depth of over 50 km).

Earthquake analyses have constrained the location and extent of the hot mantle plume immediately beneath the crust and his work has also identified zones in the crust including small amounts of molten rock beneath the rift itself, that have emerged from this plume.

This indicates that oceanic processes are apparently becoming dominant in this transitional stage of rifting, as a hot plume deep in the mantle causes melting then upwelling of buoyant molten rocks that cool in the form of elongated dykes in the crust. Dave Cornwell added:

“My results help to show that the Ethiopian Rift has matured from a purely continental rift, stretched and faulted by plate tectonic stresses, to a rift with a continental framework that is being injected with the molten rock. This represents the first few bricks in building a new ocean floor. It’s just a shame that it will take millions of years to complete!”