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

Abstract : We report in-situ dating, and Hf and O-isotope studies of zircon crystals, together with electron microprobe imaging of garnet crystals from a migmatitic diorite containing noritic globules, in the Ursuya massif (French Pyrenees). Diorite zircon crystals have old inherited cores and 295±2Ma rims, while those in the norite are homogeneous, with lower U and Pb, and higher Th and Th/U ratios than in the diorite zircon rims. The 295Ma dates represent the crystallization age of hybridised crustal melts. Norite zircon crystals have similar ages (298±3Ma) to the diorite zircon rims, interpreted as the crystalliza-tion age of the norite. Hf isotopes indicate that the noritic magmas were already crustally contaminated prior to intrusion at their present locations. The contrasting behaviours of slow- and fast-diffusing species within garnet (e.g. P vs Ca) caused sharp P and diffuse Ca core-rim transitions. Modelling of garnet Ca diffusion profiles suggests a duration of 2±1 Myr for the magma interactions in the deep crust. Integrated with granite dating, these data provide insights into pulsations in the regional thermal event that concluded the Hercynian orogenic cycle.
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https://hal.uca.fr/hal-03228280
Contributor : Sylvaine Jouhannel <>
Submitted on : Tuesday, May 18, 2021 - 8:25:00 AM
Last modification on : Saturday, May 22, 2021 - 3:42:07 AM

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Daniel Vielzeuf, Jean-Louis Paquette, J. Clemens, G. Stevens, Abdelmouhcine Gannoun, et al.. Age, duration and mineral markers of magma interactions in the deep crust: an example from the Pyrenees. Contributions to Mineralogy and Petrology, Springer Verlag, 2021, 176 (5), ⟨10.1007/s00410-021-01789-2⟩. ⟨hal-03228280⟩

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