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Single-grain laser step-heating 40Ar/39Ar age spectra of particles #0288 and #0059 and #0010 providing plateau ages of 4,219 ± 35 Ma and 4,149 ± 41 Ma. The solid line indicates the width of the plateau age (i.e., the steps included in the calculation). Detailed procedure and results are provided in the Supplementary Information.
