40Ar/39Ar and unspiked 40K-40Ar dating of upper Pleistocene volcanic activity in the Bas-Vivarais (Ardèche, France)

Combined 40Ar/39Ar datings and magnetic directions for each flow point out to three successive stages in the volcanic evolution of Bas-Vivarais. Stage 1, limited to the northern part of the field, has a mean age of 187.3 ± 19.0 ka. In its southern part, Stages 2 and 3 emplaced magmas at 31.1 ± 3.9 ka and 23.9 ± 8.1 ka, respectively. These two last stages are consistent with available 14C dates but not with previous thermoluminescence data.