Two orogens – One shear belt: 1 Ga of repeated deformation along the Central Tanzanian Shear Belt

The Central Tanzanian Shear Belt (CTSB) constitutes a 300-km long W–E trending dextral shear belt that was active during Paleoproterozoic and Neoproterozoic orogenies. It formed along the southern margin of the Archean Tanzania Craton that acted as rigid indenter during both orogenies. Based on structural and microtextural methods several deformational stages have been identified. Paleoproterozoic shear is recorded in the 1.8–2.0 Ga old magmatic Usagaran Belt. This shear was accompanied by vast melt intrusions in a hot and soft crust leading to low strain and coaxial flow. It ceased in an exhumation phase with localized non-coaxial shear followed by the deposition of nonconform sediments dated around 1.9 Ga. In the Neoproterozoic, the CTSB is found as reactivated shear zones in the Usagaran Orogen and as megascale shear zone in the metamorphic Mozambique Belt. It is a release (or counterflow) structure that evolved in the course of crustal thickening in a strong crust around 0.6 Ga. Along the strike of the Neoproterozoic CTSB syntectonic conditions change from localized brittle shear along the Tanzania Craton to distributed high temperature coaxial shear in the eastern section of the orogenʹs root. This goes along with a significant change in microstructures and LPO patterns.