As specified in Douglas (1997). 40Ar/39Ar incremental thermal-release spectra were produced by incrementally heating a sample and measuring the apparent age, as reflected by 40Ar/39Ar ratios, for each thermal step. Each fraction of Ar that was released is displayed on the x-axis of the age spectra. The integrated age is the age given by the total gas measured and is equivalent to a K-Ar age. The spectrum provides a plateau age if three or more consecutive gas fractions represent at least 60% of the total gas released and are withig 2 SD of each other. The plateau age represents an approximation to the true original cooling age. Plateau ages were calculated as described in McDougall and Harrison 1988. If a plateau is not present then [...]