The role of pre-existing Precambrian structures in the development of Rukwa Rift Basin, southwest Tanzania

Abstract

In this study, Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) and aeromagnetic data are used to analyse the trends of pre-existing basement structures within the Rukwa Rift Basin. The NW-trending Rukwa Rift Basin on the western branch of the East African Rift System, southwest Tanzania, is developing on the NW-trending Paleoproterozoic Ubendian orogenic belt, a belt that experienced multiple orogenic collisions associated with subduction in Proterozoic time and comprises several distinct terranes bounded by faults or shear zones. The results obtained using magnetic edge enhancement (derivatives) methods highlight major magnetic domains identified based on their distinctive magnetic patterns in relation to geology and tectonic setting of the studied area. The results also highlight the Precambrian Chisi shear zone which trends in a NW-SE direction in the subsurface, below the Lake Beds Formation sedimentary succession of the Neogene Rukwa Rift Basin. The orientation of rift border faults and other major faults and their relationship with basement fabrics inferred from SRTM DEM and magnetic data trend mainly NW-SE, which is consistent with those of the NW-trending Paleoproterozoic Ubendian orogenic belt. Thus, Paleoproterozoic Ubendian orogenic belt structures have played a significant role on geometry and orientation of the Rukwa Rift Basin. These structures facilitated strain localisation within the border faults of the rift basin by exploiting the existence of inherited lithospheric heterogeneity. It can be concluded that the pre-existing faults and shear zones define a mechanical anisotropy in the basement of the Rukwa Rift Basin and facilitated the strain localisation within the border faults of the rift.