Variscan U-Th-Pb age for stratabound Pb-Zn mineralization in the Bossòst dome (Pyrenean Axial Zone)

Alexandre Cugerone (1) , Françoise Roger (1) , Bénédicte Cenki-Tok (1) , Emilien Oliot (1) , Jean-Louis Paquette (2)

1 Géosciences Montpellier
2 LMV - Laboratoire Magmas et Volcans

In orogens, pinpointing the timing of mineralization is often complex due to superimposition of magmatic, metamorphic and tectonic events. Unravelling the tectono-metamorphic evolution of deformed terranes is essential for understanding the formation of orogenic mineralization. In the Bossòst dome of the Pyrenean Axial Zone, undated stratabound Pb-Zn mineralization previously considered to be SEDEX-like and devoid of evidence for significant remobilization/deformation, was recently interpreted as orogenic mineralization and structurallycontrolled by Variscan tectonics. However, relations with the poly-magmatic and metamorphic events reported in the Pyrenean Axial Zone are still poorly constrained. In the Bossòst dome, laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Th-Pb dating was performed on zircon to constrain the formation ages of two undeformed granitic dykes, and on monazite to identify both the metamorphic imprint recorded by two metapelites and the formation of stratabound Pb-Zn mineralization in the Bentaillou deposit. Late-Carboniferous early-Permian magmatic zircon ages (315-280 Ma) are commonly found in these undeformed dykes (307.4 ± 4.7 Ma and 283 ± 15 Ma), consistent with the main magmatic event, extensively recorded in the Pyrenean Axial Zone. Monazite crystals with co-genetic textural relationships with stratabound sphalerite from Bentaillou were dated at 309 ± 11 Ma. We propose that the stratabound mineralization is formed during one main Variscan remobilization event associated with the first Variscan deformation event (D1) and probable metamorphic fluid circulation in pre-existing metal-rich Ordovician sedimentary levels. Moreover, monazite ages in metapelite rocks (289.1 ± 5.9 Ma and 290.0 ± 3.8 Ma) probably date both the end of high T-low P metamorphism and late fluid circulation in the Variscan tectonothermal event. Visean-Serpukhovian ages (340-325 Ma) are found in one inherited zircon and in two monazites included in garnet and staurolite, which probably record the end of the first Variscan magmatic-metamorphic event, mainly recorded in the core of the Pyrenean Axial Zone. Based on our ages and a regional synthesis, we propose a new tectono-metamorphic model for the Bossòst dome and the related formation of Pb-Zn mineralization.

Domaines: Géologie appliquée; Géochimie

Alexandre Cugerone, Françoise Roger, Bénédicte Cenki-Tok, Emilien Oliot, Jean-Louis Paquette. Variscan U-Th-Pb age for stratabound Pb-Zn mineralization in the Bossòst dome (Pyrenean Axial Zone). Ore Geology Reviews, 2021, 139, ⟨10.1016/j.oregeorev.2021.104503⟩. ⟨hal-03371640⟩