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Amazonian Mesoproterozoic basement in the core of the Ibero-Armorican Arc: ⁴⁰Ar/³⁹Ar detrital mica ages complement the zircon's tale

¹ Departamento de Geología, Facultad de Ciencias, Universidad de Salamanca, 37008 Salamanca, Spain
² Departamento de Petrología y Geoquímica, Universidad Complutense, 28040 Madrid, Spain
³ School of Earth and Environmental Sciences and Tectonics Special Research Centre, University of Adelaide, Adelaide, SA 5005, Australia
⁴ Departamento de Geología, Universidad de Jaén, 23071 Jaén, Spain
⁵ Departamento de Mineralogía y Petrología, Campus de Fuentenueva, Universidad de Granada, 18002 Granada, Spain

The ⁴⁰Ar/³⁹Ar age data on single detrital muscovite grains complement U-Pb zircon ages in provenance studies, as micas are mostly derived from proximal sources and record low-temperature processes. Ediacaran and Cambrian sedimentary rocks from northwest Iberia contain unmetamorphosed detrital micas whose ⁴⁰Ar/³⁹Ar age spectra suggest an Amazonian–Middle American provenance. The Ediacaran sample contained only Neoproterozoic micas (590–783 Ma), whereas the Cambrian sample contained three age groups: Neoproterozoic (550–640 Ma, Avalonian–Cadomian–Pan African), Mesoproterozoic- Neoproterozoic boundary (ca. 920–1060 Ma, Grenvillian-Sunsas), and late Paleoproterozoic (ca. 1580–1780 Ma, Rio Negro). Comparison of ⁴⁰Ar/³⁹Ar muscovite ages with published detrital zircon age data from the same formations supports the hypothesis that the Neoproterozoic basins of northwest Iberia were located in a peri-Amazonian realm, where the sedimentary input was dominated by local periarc sources. Tectonic slivering and strike-slip transport along the northern Gondwanan margin affected both the basins and fragments of basement that were transferred from Amazonian to northern African realms during the latest Neoproterozoic–earliest Cambrian. Exhumation and erosion of these basement sources caused shedding of detritus to the Cambrian basins, in addition to detritus sourced in the continental mainland. The apparent dominance of Rio Negro–aged micas in the Cambrian sandstone suggests the presence of unexposed basement of that age beneath the core of the Ibero-Armorican Arc.

Key Words: Iberia • detrital mica • ⁴⁰Ar/³⁹Ar geochronology • Gondwana • Ediacaran • Cambrian

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