70 m.y. of synorogenic plutonism in eastern Borborema Province (NE Brazil): temporal and kinematic constraints on the Brasiliano Orogeny

Abstract

Recent structural, petrological and geochronological work on plutons in eastern Borborema Province (NE Brazil) has helped to constrain its tectonic evolution during the Brasiliano/Pan-African Orogeny. 645-630 Ma-old plutons have been intensely affected by solid-state deformation. They show an early, shallowly to moderately-dipping foliation conformable with the regional fabric of country rocks, which is overprinted by a steeply-dipping foliation related to strike-slip shearing. Two compositional groups are recognized: (i) medium-K, epidote-bearing granodiorites, and (ii) coarse-grained granites and associated diorites. 590-580 Ma-plutons were emplaced before or at the very early stage of movement along large transcurrent shear zones, and include high-K calc-alkaline plutons and metaluminous syenites. The 590-580 Ma-old plutons underpin the change from a low-angle tectonic event to transpressive deformation. Once emplaced, these plutons in turn favored the localization of strain needed to promote nucleation of the spatially associated shear zones. Finally, two-mica leucogranites and dike swarms of widely varying compositions were emplaced around 570 Ma at the advanced stages of motion along transcurrent shear zones.