Lifetime of an ocean island volcano feeder zone: Constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40Ar/39Ar age determinations, Fuerteventura, Canary Islands

High-precision isotope dilution thermal ionization mass spectrometry (IDTIMS) UPb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. ⁴⁰Ar/³⁹Ar amphibole dating yielded ages from 21.9 0.6 to 21.8 0.3, identical within errors to the UPb ages, despite the expected 1% theoretical bias between ⁴⁰Ar/³⁹Ar and UPb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma ⁴⁰Ar/³⁹Ar age uncertainties) from closure temperatures (T_c) of zircon (699988C) to amphibole (500600C) (ii) lead loss affecting the youngest zircons or (iii) excess argon shifting the plateau ages towards older values. The combination of the ⁴⁰Ar/³⁹Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole T_c is 0.8 Ma, suggesting PX1 lifetime of 520000 to 800000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 0.07/0.08/0.15 Ma and 21.58 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope ¹⁸O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO₂-rich carbonatite-derived fluids released during contact metamorphism.