ROLE OF THE MUGHESE SHEAR ZONE IN OBLIQUE RIFTING ALONG THE RUKWA-MALAWI SEGMENT OF THE EAST AFRICA RIFT

Numerous studies have investigated the role of Precambrian structures in strain localization along the rectilinear NW-SE trending border fault system of the Rukwa-Malawi segment of the East African Rift System. The Mbozi-Rungwe domain has also been considered as the major zone of strain accommodation for relative extension between the Rukwa Rift and Malawi Rift’s North Basin. However, little is known about the structural interaction between the hinge zones of the two rifts. Analyses of high-resolution aeromagnetic data covering this area reveal a >500 km-long prominent NW-SE trending magnetic lineament representing the Ufipa Fault and its continuation along the entire southern boundary of the Mughese Shear Zone (MSZ). This magnetic lineament offsets another distinct N-S trending ~90 km-long and 300-500 m-wide magnetic lineament orientated orthogonally to it. We interpret this N-S trending lineament as a mafic dike emplaced within the MSZ during the Lower Mesozoic Karoo rifting episode which was later displaced right-laterally by strike-slip movement along the Ufipa Fault during Late Pleistocene-Holocene NW-SE-directed extension. Our results suggest that segments of the Precambrian fabric of the MSZ were initially reactivated as brittle discontinuities which later partly accommodated relative slip between the Rukwa Rift and Malawi Rift’s North Basin.