Dual continental rift systems generated by plume-lithosphere interaction
Résumé
Although many continental rifts and passive margins are magmatic, some are not1. This observation prompted endmember
views of the mechanisms driving continental rifting, where magma-rich or active rifts would be caused by deep mantle
plumes2, whereas magma-poor or passive rifts would result from the stretching of the lithosphere under far-field plate
forces3. The Central East African Rift provides a unique setting to investigate the mechanisms of continental rifting because
it juxtaposes a magma-rich (eastern) branch and magma-poor (western) branch on either side of the 250-km-thick Tanzanian
craton4. Here we investigate this contrasted behavior using a high-resolution rheologically consistent three-dimensional
thermo-mechanical numerical model. The model reproduces the rise of a mantle plume beneath a craton experiencing
tensional far-field stress. In our numerical experiments the plume is deflected by the cratonic keel and preferentially channelled along one of its sides. This leads to the coeval development of magma-rich and magma-poor rifts along
opposite craton sides, fed by melt from a single mantle source. Our numerical experiments show strong similarities
to the observed evolution of the Central East African Rift, reconcile the passive and active rift models, and demonstrate
the possibility of developing both magmatic and amagmatic rifts in identical geotectonic environments.