Negligible effect of hydrogen content on plate strength in East Africa

Continental rifting requires weak zones to exist within the strong continental plates. This weakening is thought to be induced primarily by high hydrogen contents and temperatures, as well as small grain size(1-3). An ideal location to test models of plate strength in situ is the East African Rift(4)-the best exposed continental rift on Earth-which is forming adjacent to the unrifted Tanzanian Craton. Here I use magnetotelluric data to investigate electrical conductivity, and hence hydrogen content(5,6), across the East African Rift and Tanzanian Craton. The images show that the Tanzanian Craton is extremely rich in hydrogen, whereas the parts of the continent that are being rifted are anhydrous, suggesting that high hydrogen content does not systematically reduce plate strength. Earlier deformation events(7) may have reduced the grain size of the continental lithosphere in the East African Rift(8,9) compared to the Tanzanian Craton(10,11). I therefore suggest that the localization of rifting and repeated reactivation of deformed regions may not be due to hydrogen content and is instead controlled by small grain size.