The polyphase evolution of the Seridó Belt (NE-Brazil) includes D1 crust formation at 2.3-2.1 Ga, D2 thrust tectonics at 1.9 Ga and crustal reworking by D3 strike-slip shear zones at 600 Ma. Microstructural investigations within mylonites associated with D2 and D3 events were used to constrain the tectono-thermal evolution of the belt. D2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions (600-650 °C) through grain boundary migration, subgrain rotation and operation of quartz 〈c〉-prism slip. Continued shearing and exhumation of the terrain forced the re-equilibration of high-T fabrics and the switching of slip systems from 〈c〉-prism to positive and negative 〈a〉-rhombs. During D3, enhancement of ductility by dissipation of heat that came from syn-D3 granites developed wide belts of amphibolite facies mylonites. 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