Brasiliano (Pan-African) granitic magmatism in the Pajeú-Paraíba belt, Northeast Brazil: an isotopic and geochronological approach

Abstract

The Neoproterozoic Brasiliano/Pan-African Orogeny in the Borborema Province (BP) NE Brazil, is characterized by intense granitic magmatism spatially associated with continental scale shear zones and metamorphism under high temperature conditions. U/Pb zircon and Rb–Sr whole rock data for 14 granite intrusions from the Pajeú-Paraíba Belt have ages that suggest more than 100 Ma of intrusive magmatism, which can be divided in four events: the oldest granites (between 620 and 600 Ma) are medium-to-slightly high-K calc-alkaline I-type granitoids, intruded into metagreywackes and gneiss-granites of 0.9–1.0 Ga; they are related to the peak of metamorphism and to the development of a flat lying foliation. The youngest intrusions (540–520 Ma) have geochemical signature of A-type, post-orogenic, extension-related granites, and are associated with sub-volcanic bimodal magmatism, probably contemporaneous with deposition of small sedimentary basins in the North (Iara, Jaibaras graben and Saíri) and Central (Fatima, Betânia and Carnaúbeira) Tectonic Domains of the Borborema Province; they reflect post-tectonic relaxation of the Brasiliano Orogeny. Between these episodes, two other intrusive events were identified: (1) high-K calc-alkaline granitoids and shoshonitic granitoids associated with mafic syenites, meladiorites and hornblende – biotite diorites, intruded between 590 and 581 Ma, associated with a transcurrent deformation event, and (2) alkaline post-collisional granitoids having U/Pb zircon ages of ca. 570 Ma, marking the final stage of the Brasiliano Orogeny. In the South Domain of the Borborema Province, migmatization took place between 610 and 600 Ma. Although similar ages were not found in the granitoids of the Central Tectonic Domain, field evidence suggest that migmatization followed the intrusions of the oldest (620–600 Ma) granitoids.