Age, duration and mineral markers of magma interactions in the deep crust: an example from the Pyrenees

We report in-situ dating, and Hf O-isotope studies of zircon crystals, together with electron microprobe imaging garnet crystals from a migmatitic diorite containing noritic globules, in the Ursuya massif (French Pyrenees). Diorite have old inherited cores 295 ± 2 Ma rims, while those norite are homogeneous, lower U Pb, higher Th Th/U ratios than rims. The dates represent crystallization age hybridised crustal melts. Norite similar ages (298 3 Ma) to interpreted as norite. isotopes indicate that magmas were already crustally contaminated prior intrusion at their present locations. contrasting behaviours slow- fast-diffusing species within (e.g. P vs Ca) caused sharp diffuse Ca core-rim transitions. Modelling diffusion profiles suggests duration 1 Myr for magma interactions deep crust. Integrated granite these data provide insights into pulsations regional thermal event concluded Hercynian orogenic cycle.