40Ar/ 39Ar dating of Penninic Front tectonic displacement (W Alps) during the Lower Oligocene (31–34 Ma) |
| |
| Authors: | T Simon-Labric Y Rolland T Dumont T Heymes C Authemayou M Corsini M Fornari |
| |
| Institution: | Institut de Géologie et Paléontologie, UNIL, bâtiment Humense, CH1015 Lausanne, Switzerland;;Géosciences Azur, UMR6526-CNRS, UNS, 28 Av. Valrose, BP 2135, 06103 Nice, France;;LGCA, UMR5025-CNRS, OSUG, 1381 rue de la Piscine, 38031 Grenoble, France |
| |
| Abstract: | Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40Ar/39Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite–phengite thermobarometry yields 10–15 km and T ～280 °C, while 40Ar/39Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40Ar/39Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites. |
| |
| Keywords: | |
|
|
