The Rio Salgado fold belt, north-northwest of the Transversal Zone-Borborema Province (PB-CE)

Abstract

The Piancó-Alto Brígida (SPAB) Fold System was defined as a branching system of Neoproterozoic orogens at the central‑western portion of the Transversal Zone-Borborema Province. The discrimination Rio Salgado Fold Belt (FDRS) is here proposed for the northernmost SPAB branch. This belt (FDRS), which is partially covered by the Phanerozoic sediments of the Araripe Basin, is delimited to the north by the Patos Lineament (here considered as a continental boundary transform) and its southern border is characterized by a series of paleoproterozoic basement inliers. The SPAB southern and southeastern branches are intruded by dozens of (“I”-type) stocks and batholiths of a continental magmatic arc, which is positioned from the northeastern coastal area of Paraíba to the Piauí outback (ca. 800 km). FDRS is located between this magmatic arc and the Patos Lineament and is mainly constituted by fine siliciclastic sequences of high-frequency rhythmicity, with local intercalations of acid, intermediary and basic volcanic sheets. The regional metamorphism corresponds to the low greenschist facies (sericite-chlorite-biotite). Three complete lithostratigraphic and structural regional cross sections transversal to FDRS were performed and five informal stratigraphic units recognized. Preliminary geochronological surveys (U-Pb, zircon) indicate regional sedimentation younger than 650 Ma. Three different phases of regional folding were identified and will here be discussed. FDRS general geological and tectonic characteristics, as well as the nature of its basement, point to the orogenic development of a forearc basin in Late Cryogenian times.