Petrogenesis of mafic to felsic plutonic rock associations: the calc-alkaline Quérigut complex, French Pyrenees

The Quérigut mafic–felsic rock association comprises two main magma series. The first is felsic comprising a granodiorite–tonalite, a monzogranite and a biotite granite. The second is intermediate to ultramafic, forming small diorite and gabbro intrusions associated with hornblendites and olivine hornblendites. A U–Pb zircon age of 307 ± 2 Ma was obtained from the granodiorite–tonalites. Contact metamorphic minerals in the thermal aureole provide a maximum emplacement pressure of between 260 and 270 MPa. Petrographic characteristics of the mafic and ultramafic rocks suggest crystallization at <300 MPa, demonstrating that mantle-derived magmas ascended to shallow levels in the Pyrenean crust during Variscan times. The ultramafic rocks are the most isotopically primitive components, with textural and geochemical features of cumulates from hydrous basaltic magmas. None of the mafic to ultramafic rocks have depleted mantle isotope signatures, indicating crustal contamination or derivation from enriched mantle. Origins for the diorites include accumulation from granodiorite–tonalite magma, derivatives from mafic magmas, or hybrids. The granitic rocks were formed from broadly Proterozoic meta-igneous crustal protoliths. The isotopic signatures, mineralogy and geochemistry of the granodiorite–tonalites and monzogranites suggest crystallization from different magmas with similar time-integrated Rb/Sr and Sm/Nd isotope ratios, or that the granodiorite–tonalites are cumulates from a granodioritic to monzogranitic parent. The biotite granite differs from the other felsic rocks, representing a separate magma batch. Ages for Quérigut and other Pyrenean granitoids show that post-collisional wrenching in this part of the Variscides was under way by 310 Ma.