Lithospheric Controls on the Rifting of the Tanzanian Craton at the Eyasi Basin, Eastern Branch of the East African Rift System

Abstract

AbstractContinental rifts most often nucleate within orogenic belts. However, some studies in the East African rift system have shown that continental rifts can also develop within cratons. This work investigated the ~1.5‐Ma Eyasi basin, which propagates in a WSW direction into the Tanzanian craton. The basin is located where the eastern branch of the East African rift system transitions from a narrow rift (~70 km wide) to the wider (~300 km wide) North Tanzanian Divergence. Unlike the rest of the eastern branch segments, the Eyasi basin does not follow the Mozambique orogenic belt located on the eastern margin of the Tanzanian craton. This work generated lithospheric‐scale sections across the basin using (1) digital elevation model to map surface rift‐related brittle structures; (2) aeromagnetic data to determine the depth to the Precambrian basement; and (3) World Gravity Model 2012 to estimate crustal and lithospheric thickness by applying the two‐dimensional radially averaged power spectral analysis and two‐dimensional forward gravity modeling. These cross sections show that the Eyasi basin nucleates within a previously unidentified suture zone within the Tanzanian craton and that this suture zone is characterized by thinner lithosphere that can be as thin as ~95 km. This zone of thinner lithosphere is offset southeastward from the surface expression of the Eyasi basin and might have facilitated the formation of other basins further south. Furthermore, the lithospheric thickness map indicates that the Tanzanian craton is heterogeneous and possibly composed of multiple smaller cratonic fragments.