Produção Nacional
Revisado por pares
Geochronology of mafic magmatism and hydrothermal alteration during early stages of South Atlantic opening
2021; Elsevier BV; Volume: 314; Linguagem: Inglês
10.1016/j.gca.2021.08.017
ISSN1872-9533
AutoresKarine Zuccolan Carvas, Paulo Vasconcelos, Leila Soares Marques, Teresa Ubide, Isabela de Oliveira Carmo, Marly Babinski,
Tópico(s)Geochemistry and Geologic Mapping
Resumo• Low-TiO 2 mafic dykes intruded the Brazilian southeast margin at ~132–133 Ma. • The dykes were hydrothermally altered at ~106–105 Ma and between 60–30 Ma. • Fluid percolation affected LILE and light REE compositions of the intrusions. • Magmatism drove fluid circulation, partially dissolving marginal basin evaporites. 40 Ar/ 39 Ar laser incremental-heating geochronology of whole-rock fragments and minerals from primitive subalkaline mafic dykes from the Cabo Frio Tectonic Domain, southeastern Brazil, reveals a complex combination of intrusive ages, apparent ages affected by excess argon, and ages that record late-stage hydrothermal alteration. Incremental-heating analysis of encapsulated magmatic amphibole-biotite clusters reveals a minimum intrusive age of 132.83 ± 0.30 Ma. Sericitized plagioclase crystals show the percolation of K-rich fluids at ~106 Ma. Albitized plagioclase phenocrysts suggest the percolation of Na-rich fluids in the 60–30 Ma interval. Hydrothermal alteration events overlap in time with pulses of alkaline magmatism in the extending Brazilian crust, suggesting a link between magmatic activity and generation of fluid circulation cells along the margin and adjacent sedimentary basins. Evidence for pervasive hydrothermal re-setting of the K-Ar system in the Cabo Frio Tectonic Domain dykes suggests that young 40 Ar/ 39 Ar geochronology results obtained for mafic dykes here and elsewhere along the continental margins may not record multiple intrusive events, reflecting instead partial or total resetting of the K-Ar system by water-rock interaction during fluid circulation.
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