‡ fraction ignored in the isochron given in the figure Note: The integrated results for the second experiment are given for comparison. It is necessary to take in account that these results are not accurate since for fraction 'n' was very close in size to the blank, therefore for this fraction mass 36 is not reliable and no age information can be reported. However, since this is a very small fraction with only ~0.82% of the 39 Ar released, it has very little effect in the integrated results. Supplementary Data Table 2. Ar-Ar analytical data of the Sample G5, Calderones Formation (ignimbrite) Long. W Lat. N 20.9837° 101.2414° Sample G5. Laser step-heating experiments with plagioclase concentrate