“Inverted” zircon and apatite (U–Th)/He dates from the Front Range, Colorado: High-damage zircon as a low temperature (<50◦C) thermochronometer
Johnson JE, Flowers RM, Baird GB, Mahan KH. 2017. “Inverted” zircon and apatite (U–Th)/He dates from the Front Range, Colorado: High-damage zircon as a low temperature (<50◦C) thermochronometer. Earth and Planetary Science Letters. 466:80-90
Zircon (U–Th)/He (ZHe) data were acquired for 23 Proterozoic basement samples from an E–W transect through the Colorado Front Range to evaluate whether metamict zircons yield sensible (U–Th)/He data patterns and useful thermal history information. The 112 ZHe dates vary from 147 to 7 Ma, define positive and negative date–eU correlations, and are younger than titanite (U–Th)/He dates that range from 976 to 614 Ma. At moderate to high alpha dose of , zircons from the range core yield Laramide ( Ma) dates, whereas those within ∼15 km of the range front yield Miocene ( Ma) results. The He dates for the high alpha dose zircons are reproducible within each sample suite despite their visibly metamict character. The ∼20 Ma range front ZHe dates are younger than apatite (U–Th)/He (AHe) dates ( Ma) and published apatite fission-track data (65–45 Ma) for the same and nearby samples. Thermal history simulations can reproduce the first-order range front date–eU patterns and ZHe–AHe date inversion, but the high-damage zircons are more He retentive than predicted by the zircon damage He kinetic model. The ∼20 Ma ZHe dates may be explained by reheating from hydrothermal fluids along range front faults. The results demonstrate the promise of using He data for high-damage zircons to detect low-temperature (<50 °C) events within and below the temperature sensitivity of the AHe system.
- Type
- Journal Article
- Authors
- Johnson, Joshua; Flowers, Rebecca; Baird, Graham; Mahan, Kevin
- Units
- ROMO
- Keywords
- apatite, Colorado Front Range Rocky Mountains, thermochronology:(U-Th)/He, zircon