Ophiolitic material from the nappe des Gets has been dated by conventional K/Ar and by total fusion ⁴⁰Ar/³⁹Ar methods. These ophiolites appear to belong to two. temporally distinct, magmatic episodes: — The first, of Lower to Middle Jurassic age. includes the gabbros and diabases associated with serpentinites. — The second, of Maastrichtian age. includes albite-chlorite diabases formed in submarine basaltic eruptions which probably occurred at about the same time as flysch sedimentation in Albian-Cenomanian times. Therefore, the age measured is considered to date a metamorphic event only. Finally, it should be noted that the albite-chlorite diabases from the col de la Ramaz zone seem to have ages older than other albite-chlorite diabases.