Timing and duration of meteoric water infiltration in the Quiberon detachment zone (Armorican Massif, Variscan belt, France)

Camille Dusséaux, Aude Gébelin, Philippe Boulvais, Gilles Ruffet, Marc Poujol, Nathan Cogné, Yannick Branquet, Catherine Mottram, Fabrice Barou, Andreas Mulch

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Abstract

Assessing the geochemical signature and the role of fluids in a key Variscan detachment zone demonstrates the link between crustal deformation, thermo-mechanical events and Variscan mineralization. We document meteoric fluid infiltration into the ductile segment of the Late-Carboniferous Quiberon detachment zone (QDZ), when synkinematic muscovite and tourmaline crystallized and equilibrated with deuterium-depleted surface-derived fluids during high-temperature deformation. Titanium-in-muscovite thermometry supported by microstructures indicate that syntectonic isotope exchange between fluids and hydrous minerals occurred above 500 °C. 40Ar/39Ar muscovite data (∼319–∼303 Ma) and U(–Th)/Pb geochronology on zircon, monazite and apatite (∼318–∼305 Ma) from syntectonic leucogranites together with microstructural and geochemical (U and REE contents) data suggest that meteoric fluid-rock-deformation interaction started at ∼320 Ma and played a major role in leaching uranium at ∼305 Ma. U–Th/Pb data (∼330–∼290 Ma) from migmatites located below the QDZ strengthen the idea that meteoric fluid infiltration, detachment activity, syntectonic leucogranite emplacement and migmatization were coeval and allowed the development of a sustained hydrothermal system.
Original languageEnglish
Article number104546
Number of pages19
JournalJournal of Structural Geology
Volume156
Early online date13 Feb 2022
DOIs
Publication statusPublished - 1 Mar 2022

Keywords

  • Variscan
  • detachment
  • shear zone
  • hydrous silicates
  • hydrogen isotope
  • 40Ar/39Ar
  • U(–Th)/Pb
  • geochronology
  • fluid-rock interaction
  • meteoric fluids

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