Accommodation of the extension regime of the East African rift system within the Tanzania Craton after impingement of the eastern branch on the Craton

Abstract

Variations in stress regimes within the Tanzania Craton and at the suture between the Pan-African Mozambique Belt (MB) and the Craton are evaluated using stress tensor inversion of focal mechanisms. The change in fault pattern and the difference in earthquake focal mechanisms along these faults as the Eastern branch (EB) of the East African rift system (EARS) crosses into the Craton from MB have also been examined. Results from the stress inversion indicate that as the fault arrays change, when the EB crosses into the Craton, from NNE-SSW in the MB to NE-SW and NW-SE in the Eyasi-Wembere (EWR) and Bahi-KwaMtoro (BKR) regions within and along the Craton boundary, so does the stress pattern. The strain in the area is accommodated primarily by dextral strike-slip faults along NE- and NW-striking faults in EWR and BKR, respectively. The observed coexistence pattern of normal and strike-slip earthquakes in EWR is explained by border fault linkage through transfer faults. The pattern in BKR argues fault linkage through transfer faults where two rift segments, the southern extent of Eyasi and Manyara segments, are linked by an oblique dextral transfer zone. The findings also show that the overall WNW-ESE extension direction introduced by the EARS into the Craton is accommodated by two orthogonal-oriented stresses (Shmin) within the Craton, showing NNW-SSE and ENE-WNW in EWR and BKR, respectively. The different stress orientations in EWR and BKR might be attributed to the resistance exerted by the Craton, leading to restricted deformation along the Craton margin and, in some parts, to lateral delamination of the Craton. The variations in the stress field lead to differences in the fault array as depicted by strain accommodation in normal and strike-slip faults in places like Eyasi-Wembere and Balangida depression in the north and BKR in the south.