Role of Strike-Slip Faulting in the Evolution of a Young Rift Basin: Malawi Rift, East Africa

Mortimer, Estelle¹, Douglas Paton², Chris Scholz³, Manfred Strecker¹ (1) University of Potsdam, Potsdam, Germany (2) Colorado School of Mines, Golden (3) University of Syracuse, Syracuse

The East African Rift system is the best modern example of early continental rifting. The Malawi Rift is characteristic of the EARs western branch; in which each basin exhibits similar bathymetry, border-fault and fault segment length. We investigate the north basin of the Malawi Rift, in which the degree and possible timing of strike-slip deformation remains an issue of some debate. The NW-SE orientation differs to the N-S orientation of basins farther south in the rift due to an underlying pan-African foliation.

Our data reveal the border-fault and intra-basin structures nucleated during orthogonal (ENE) extension. During this time (>8.6 to ~0.4 Ma) intra-basin faults synthetic to the west-dipping border-fault nucleated, while strain localised onto the border-fault. At 0.4 Ma, the basin became characterised by dextral strike-slip deformation: flower-structures developed above the greatest throw intra-basin faults, and transfer faults nucleated adjacent to the border-fault system. We attribute this change in fault mode to a rotation of extension orientation (to NW) such that, in contrast to basins farther south in the rift, the north basin undergoes oblique extension.