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Contemporaneous alkaline and tholeiitic magmatism in the Ponta Grossa Arch, Paraná-Etendeka Magmatic Province: Constraints from U–Pb zircon/baddeleyite and 40 Ar/ 39 Ar phlogopite dating of the José Fernandes Gabbro and mafic dykes

2017; Elsevier BV; Volume: 355; Linguagem: Inglês

10.1016/j.jvolgeores.2017.01.018

1872-6097

Vidyã Vieira de Almeida, Valdecir de Assis Janasi, Larry M. Heaman, Barry Shaulis, Maria Helena Bezerra Maia de Hollanda, Paul R. Renne,

earthquake and tectonic studies

We report the first high-precision ID-TIMS U–Pb baddeleyite/zircon and 40Ar/39Ar step-heating phlogopite age data for diabase and lamprophyre dykes and a mafic intrusion (José Fernandes Gabbro) located within the Ponta Grossa Arch, Brazil, in order to constrain the temporal evolution between Early Cretaceous tholeiitic and alkaline magmatism of the Paraná-Etendeka Magmatic Province. U–Pb dates from chemically abraded zircon data yielded the best estimate for the emplacement ages of a high Ti–P–Sr basaltic dyke (133.9 ± 0.2 Ma), a dyke with basaltic andesite composition (133.4 ± 0.2 Ma) and the José Fernandes Gabbro (134.5 ± 0.1 Ma). A 40Ar/39Ar phlogopite step-heating age of 133.7 ± 0.1 Ma from a lamprophyre dyke is identical within error to the U–Pb age of the diabase dykes, indicating that tholeiitic and alkaline magmatism were coeval in the Ponta Grossa Arch. Although nearly all analysed fractions are concordant and show low analytical uncertainties (± 0.3–0.9 Ma for baddeleyite; 0.1–0.4 Ma for zircon; 2σ), Pb loss is observed in all baddeleyite fractions and in some initial zircon fractions not submitted to the most extreme chemical abrasion treatment. The resulting age spread may reflect intense and continued magmatic activity in the Ponta Grossa Arch.