Aborted propagation of the Ethiopian rift caused by linkage with the Kenyan rift

Continental rift systems form by propagation of isolated rift segments that interact, and eventually evolve into continuous zones of deformation. This process impacts many aspects of rifting including rift morphology at breakup, and eventual ocean-ridge segmentation. Yet, rift segment growth and interaction remain enigmatic. Here we present geological data from the poorly documented Ririba rift (South Ethiopia) that reveals how two major sectors of the East African rift, the Kenyan and Ethiopian rifts, interact. We show that the Ririba rift formed from the southward propagation of the Ethiopian rift during the Pliocene but this propagation was short-lived and aborted close to the Pliocene-Pleistocene boundary. Seismicity data support the abandonment of laterally offset, overlapping tips of the Ethiopian and Kenyan rifts. Integration with new numerical models indicates that rift abandonment resulted from progressive focusing of the tectonic and magmatic activity into an oblique, throughgoing rift zone of near pure extension directly connecting the rift sectors.

This research was supported by the National Geographic Society (Grant #9976–16, P.I.
G. Corti). We thank the DigitalGlobe Foundation for providing the satellite image in
Fig. 3. We warmly thank Antonio Zeoli for the processing of the satellite images and
Pablo Tierz for valuable discussions. Inversion of fault-slip data and volcanic alignments
was obtained using Win-Tensor, a software developed by Dr. Damien Delvaux, Royal
Museum for Central Africa, Tervuren, Belgium. D.K. is supported by NERC grant NE/
L013932. F.I.-K. is supported by the ECLIPSE Program funded by the New Zealand
Ministry of Business, Innovation and Employment. S.B. and A.G. are supported by the
Helmholtz Young Investigators Group CRYSTALS (VH-NG-1132). Numerical models
were conducted on HLRN cluster Konrad. The Ar/Ar laboratory at ISTO is supported by
LABEX Grant “VOLTAIRE”.