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

Giacomo Corti,Paola Molin,Raffaello Cioni,Ilaria Isola,Asfaw Erbello,Sascha Brune,Zara Franceschini,Francesco Mazzarini,Stéphane Scaillet,Ameha Muluneh,Federico Sani,Finnigan Illsley-Kemp,Anne Glerum,Derek Keir

doi:10.1038/s41467-019-09335-2

Abstract

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.

Highlights

Continental rift systems form by propagation of isolated rift segments that interact, and eventually evolve into continuous zones of deformation
This rift is part of the Turkana depression, a lowland located between the uplifted East African and Ethiopian plateaus characterised by a complex deformation pattern, which results from the interaction between the Ethiopian and Kenyan rifts (Fig. 1)
The Lake Turkana basin corresponds to the northwestward propagation of the Kenyan rift via the Suguta valley, whereas the Ririba rift is suggested to result from the southward propagation of the Ethiopian rift[13,14,15]

Summary

Introduction

Continental rift systems form by propagation of isolated rift segments that interact, and eventually evolve into continuous zones of deformation. Within this wide region of tectonic activity, extension is clustered within different sub-parallel regions of deformation, corresponding to the basin hosting Lake Turkana, the Kino Sogo fault belt and the Ririba rift itself (Fig. 1). Numerical and physical modelling of rift linkage suggests that the anomalous breadth of the volcanic and tectonic activity in the Turkana depression has been likely controlled by the presence of a pre-existing heterogeneity in the Turkana lowland, corresponding to a system of NW-SE-trending Mesozoic-Paleogene grabens[17] transversal to the trend of the Ethiopian and Kenyan rifts (Supplementary Note 1). The results suggest that the southward propagation of the Ethiopian Rift to form the Ririba rift during the Pliocene was short-lived and aborted close to the Pliocene-Pleistocene boundary, with the Ethiopian and Kenyan rifts instead directly linking by a narrow, throughgoing rift zone in the Turkana depression

Methods

Results

Conclusion