PRE-EXISTING LITHOSPHERIC SCALE STRUCTURES FACILITATE OBLIQUE RIFTING: EVIDENCE FROM THE RUKWA-MALAWI SEGMENT OF THE EAST AFRICAN RIFT SYSTEM

Our understanding of strain localization processes within the lithosphere remains limited, as there are only a few locations on earth where they can be directly observed. In this study, we investigate the role of pre-existing zones of weakness presented by lithospheric-scale shear zones in influencing oblique rifting kinematics along the Rukwa-Malawi segment of the East African Rift System (EARS). The NW-trending Neoproterozoic Mughese Shear Zone (MSZ) separates the Paleoproterozoic Ubendian Belt from the Mesoproterozoic Irumide Belt, and underlies the hinge zones of the Cenozoic Rukwa Rift and Malawi Rift North Basin. We analyzed Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) data and filtered aeromagnetic data to elucidate the relationship between the brittle rift structure and the MSZ ductile fabric. We found that the MSZ-related magnetic lineaments coincide with: (1) the Ufipa Fault, which is the southwestern border-fault of the Rukwa Rift; (2) a dextral strike-slip fault (the Mughese Fault) that bounds the southwestern edge of the Mbozi block; and (3) the Mbiri Fault, a major hinge-zone fault in the North Basin. Fault-scarp and minimum fault-throw analyses along the delineated Ufipa-Mughese-Mbiri fault system suggest that Cenozoic strain localization along the Rukwa-Malawi Rift North Basin are actively facilitated by reactivation along the MSZ through regional oblique extension.