Sinistral reactivation of the Transbrasiliano Lineament: Structural and geochronological evidences in the Cariré Granulite Zone, Borborema Province - NE Brazil

The Precambrian basement in the region of Cariré, northeast Ceará Central Domain, NE Brazil, comprises essentially dioritic gneisses and granodiorites formed under high-grade metamorphism conditions. The granulites occur frequently as metric bodies or as boudins in mylonitic/cataclastic orthogneiss matrix, within shear zones related to Transbrasiliano Lineament. Geological mapping in this region confirmed a mylonitic foliation trending ∼ N20E and sub vertical dip (∼70°) towards NW or SE. Hornblende, biotite and orthopyroxene crystals define the lineation of the main extensional direction, with sub horizontal S-SW plunge (∼5-10°). Many outcrops show a large variety of structural elements linked to ductile deformation and typical structural elements representing the transition from ductile to brittle domains. Felsic and mafic dykes of various dimensions and both ductilely and brittlely deformed are found frequently. Analysis of kinematic indicators in the lineament shows both dextral and sinistral shear sense, although ductile dextral shear is more frequent. Structures developed in shallower crustal conditions, including micro-shear, tension gashes and faults trending N12E-N20E, show sinistral kinematics. Zircon crystals obtained from felsic dykes, dislocated by faults parallel to the regional trend of the Transbrasiliano Lineament, display four groups of concordant ages, the most recent of which is ca. 460 Ma. Our data suggest that throughout its complex history, the Transbrasiliano Lineament has been reactivated under brittle conditions from the Upper Ordovician onwards.