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40Ar/ 39Ar dating of Penninic Front tectonic displacement (W Alps) during the Lower Oligocene (31–34 Ma)

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.
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https://hal-insu.archives-ouvertes.fr/insu-00411593
Contributor : Pascale Talour <>
Submitted on : Friday, August 28, 2009 - 10:36:35 AM
Last modification on : Monday, October 12, 2020 - 11:10:18 AM

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T. Simon-Labric, Yan Rolland, Thierry Dumont, Thomas Heymes, Christine Authemayou, et al.. 40Ar/ 39Ar dating of Penninic Front tectonic displacement (W Alps) during the Lower Oligocene (31–34 Ma). Terra Nova, Wiley-Blackwell, 2009, 21 (2), pp.127-136. ⟨10.1111/j.1365-3121.2009.00865.x⟩. ⟨insu-00411593⟩

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