Crystallisation and fast cooling of the (meta)gabbro from the Chenaillet ophiolite (Western Alps): In-situ U Pb dating of zircon, titanite, monazite and xenotime in textural context

The Chenaillet ophiolite, South of Montgenèvre (France), represents a preserved portion the alpine ocean. gabbros form lenticular bodies 50 to 200 m thick and few hundreds meters wide. They are intrusive in serpentinites often overlain by pillow-lavas. Plagiogranite/albitite veins rare volumetrically negligible. petrology gabbro s.s. show great details progressive cooling massif, clinopyroxene rimmed brown green amphibole +/− ilmenite/titanite. Thermometry on these assemblages indicates retrograde temperature evolution from late magmatic subsolidus, between 950 900 °C, 800–750 600–500 °C. In shear zone, string titanite associated with monazite xenotime ilmenite is located millimetric greenschist layer whose estimated at 600–550 Accessories chemistry this sample allowed situ dating LA-ICPMS thin section textural context. same sample, we performed UPb zircon dating, constraining age, as well monazite, for metamorphic evolution. Tera-Wasserburg diagram, yield 161.3 4.0 Ma, 161.5 2.4 Ma 158.4 2.3 lower intercept ages, respectively, while an age 161.0 0.8 Ma. Finally, dated albitite vein also yields 161.8 ± 1.7 age. These similar ages within analytical uncertainties that magmatism metamorphism were concomitant. Thermal modelling predicts 150 gabbroic massif crystallizes hundred years cools down several thousand years. This consistent reported our study showing records fast cooling. development required multiple fluid infiltrations during studied samples, 4 types titanites could be distinguished based their chemistries. 3 variously depleted REE interpreted related water-driven fluids another type has up 10% REE, Y Nb suggest possible felsic source. two potential sources water promoting sea water-derived exsolved veins.