Tectonic significance of the Florianópolis Dyke Swarm, Paraná-Etendeka Magmatic Province: A reappraisal based on precise U-Pb dating

The first precise ID-TIMS U-Pb baddeleyite/zircon dating of dykes representative of the main activity in the Florianópolis Dyke Swarm (Paraná-Etendeka Magmatic Province, south Brazil) reveals a restricted age range (134.7 ± 0.3 to 133.9 ± 0.7 Ma). This is at least 5 Ma older than indicated by previous 40Ar/39Ar stepwise heating dating, and precludes a direct relationship with syn-rifting magmatism connected with opening the south Atlantic Ocean. Instead, as indicated by their age and geochemical signature, these dykes are feeders to the nearby Urubici lavas (and coeval Khumib lavas in Etendeka). These new geochronological results also cast doubt on a large (> 10 Ma) time span for the emplacement of the Florianópolis Dyke Swarm implied by 40Ar/39Ar dates, but the determination of its upper age limit still requires accurate dating of younger, low-volume fine-grained dykes with distinct low-Ti chemistry; crystals suitable to U-Pb dating were not obtained thus far from these dykes.