Offshore granulites from the Bay of Biscay margins: fission tracks constrain a Proterozoic to Tertiary thermal history |
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| Authors: | Bernhard Fügenschuh Nikolaus Froitzheim Raymond Capdevila Gilbert Boillot |
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| Institution: | Geologisch-Paläontologisches Institut, Bernoullistrasse 32, CH-4056 Basel, Switzerland;;Geologisches Institut, Universität Bonn, Nussallee 8, D-53115 Bonn, Germany;;Géosciences Rennes, UniversitéRennes 1, 263, av. du Général Leclerc, F-35042 Rennes cedex, France;;Géosciences Azur, Observatoire Océanologique, BP 48, F-06235 Villefranche sur Mer, France |
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| Abstract: | Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 ± 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 ± 58 Ma (zircon), indicating post‐Variscan cooling. Apatite from this sample gave 52 ± 2 Ma, interpreted as final cooling after ‘Pyrenean’ thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 ± 7 and 120 ± 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 ± 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high‐grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia. |
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