U-Pb Shrimp-RG zircon ages of Variscan igneous rocks from the Guilleries massif (NE Iberia pre-Mesozoic basement). Geological implications

One diorite sheet, syntectonic with the dominant D2 foliation in the Guilleries massif, 50 km south of the Variscan Pyrenean axial zone, has provided an U-Pb age of 323.6 ± 2.8 Ma, one of the oldest in that part of the Variscan basement. This age seems to be the same as that of the sillimanite-grade syn-D2 metamorphism in the deepest part of the massif; it is clearly separated from that obtained in three syn-extensional D3 leucogranite veins (305.3 ± 1.9; 301.5 ± 1.7; 299.0 ± 2.3 Ma) and the coeval biotite granites (305.9 ± 1.5 Ma). The leucogranites are 20 Ma younger than the syn-D2 diorite and the sillimanite-grade metamorphism. They are considered the melting-induced products in the host rocks, at a deeper level than that of the present outcropping of the mantle-related biotite granites during the extensional collapse (D3) of the chain in the Lower Stephanian. © 2008 Académie des sciences.