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Two samples of volcanic rocks were analyzed by the 40Ar/39Ar method. A whole rock and a plagioclase–rich groundmass concentrate were irradiated in the uranium enriched research reactor of McMaster University in Hamilton (Ontario, Canada). The argon isotopic analysis was performed at the geochronologic lab of Centro de Investigación Científica y Educación Superior de Ensenada (CICESE), using both a MS–10 and a VG5400 mass spectrometers. The sample analyzed with the MS–10 was step–heated with a double wall Modifications Ltd Ta furnace, while in the experiments performed with the VG5400 mass spectrometer the argon extraction line uses a Coherent Innova 70C argon–ion laser to heat the sample. The age spectra, 37ArCa/39ArK vs 39Ar, and 36Ar/40Ar vs 39Ar/40Ar correlation diagrams, are given in the Geochronology section. Errors are reported at 1 –sigma level for all samples. Details of the experiments are shown in Table A1 of the electronic supplement. The argon isotopes were corrected for discrimination, blank, decay of 37Ar and 39Ar and interference contributions of argon isotopes derived from Ca, Cl and K. The decay constants recommended by Steiger and Jäger (1977) were used in the age calculations. All linear regressions were performed with the equations presented by York et al. (2004).