Chemical (non-isotopic) and isotopic dating of Phanerozoic zircon—A case study of durbachite from the Třebíč Pluton, Bohemian Massif

Although chemical (non-isotopic) U–Th–Pb dating of monazite by electron microprobe is well-established, dating of zircon by this method is still controversial. Relatively U-rich zircon (up to 2500 ppm of U) from the Třebíč Pluton provides a test case for the technique. Zircon grains are commonly partially or completely metamict, and therefore susceptible to Pb loss and common Pb contamination. Using Ca and K contents as indicators of damaged or contaminated zircon, a CHIME (Chemical U–Th–total Pb method) age of 347.8 ± 18 Ma was obtained from data with < 0.03 wt.% of CaO and K2O, and > 0.0062 wt.% of PbO. This age was confirmed by isotopic U–Pb SHRIMP dating (341.6 ± 2.8 Ma). These results are in agreement with previous estimates for the timing of durbachitic intrusions into the root of the Variscan orogen and from the Variscan basement incorporated into Western Alps, between 343 and 332 Ma.