Thirty K-Ar ages are presented. They have been measured on gabbros and diabases. Most age determinations have been done on fresh basaltic hornblende. Some samples, including typical spilitic submarine diabases, were dated using the total rock. The results may be distributed in three groups. In the first one, with hornblende gabbros-diabases, ages range between 200 and 100 My. with two frequency maxima at 180-165 My. and 150-135 My. In the second one, with submarine lava flows, ages range between 120 and 70 My. At last, two ages of 285 and 303 My. have been obtained on diabases from the «Zone du Col de la Ramaz». The problem of metamorphism, spilitization and alteration of the dated rocks is discussed. The volcanic activity related to sea floor spreading phase before alpine orogeny appears to be of early Jurassic age while dated lava flows seem to be cretaceous. The diabasic lenses of the «Zone du Col de la Ramaz» should belong to the hercynian cycle.