The importance of high precision in the evaluation of U-Pb zircon age spectra

We present high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon data from the Carboniferous Punteglias granodiorite Central Alpine basement in Aar massif Switzerland. These analyses yield complex age spectra consisting of both concordant and normally discordant dates, which form a linear array indicative mixing two components within individual crystals. While upper intercept reflects growth during Variscan magmatism, lower 24 ± 11 Ma is coincident with orogeny. There poor evidence cathodo-luminescence imagery that magmatic may have younger overgrowths, therefore, we pretreated an aliquot physical abrasion followed by chemical to remove any potential later directly date initial domains zircon. This pretreatment significantly reduced dispersion yielded 335.479 0.041 for crystallization granodiorite. Due effectiveness this pretreatment, interpret was overgrown Detangling observed complications zircons largely possible due particularly high analytical precision ID-TIMS dates made it detect discordance between 206Pb/238U 207Pb/235U systems. Lower-precision would not allow identification such two-component mixture lead analytically points spreading over 105 106 years, potentially leading erroneous scientific interpretation. As example, model hypothetical situations simple concordia space demonstrate effect on ability accurately geological models complicated spectra. Combining these new modeling results highlights importance choosing optimal, and/or sample pre-treatment challenge interpreting terms age.