U-Pb-age from undeformed granite pebbles in Carboniferous Culm conglomerates: new geochronological constrains on the Variscan events in the Pyrenees

Abstract

U-Pb ages of zircon and apatite in undeformed granite pebbles of synorogenic Carboniferous Culm conglomerates confirm the existence of an early Carboniferous (Visean to Bashkirian) magmatic event in the core of the Pyrenees. In this so-called Axial Zone, early Carboniferous magmatism developed in at least two main pulses, at ca. 340 Ma and ca. 320 Ma. Obtained ages constrain a mid-Bashkirian maximum age (ca. 320 Ma) for the base of Bellver Culm conglomerates. Together with the well-expressed late Variscan Moscovian-Asselian (ca. 310 to 295 Ma) granites that crosscut Culm rocks, this Visean to Bashkirian magmatism depicts three pulses of Variscan magmatism, grouped in two cycles of magmatic and tectono-thermal events recorded in the basement rocks of the Pyrenean Axial Zone. This complex Variscan evolution argues against previously proposed models claiming for a synkinematic emplacement of the Moscovian-Asselian granites linked to the main Variscan deformational events. Data obtained confirm the occurrence of Variscan events from the Visean to the Moscovian-Asselian in the Pyrenees. In this way, the Variscan basement rocks of the Pyrenees exhibit an evolution that aligns with that described for the rest of the European Variscan realm.