Late Pleistocene zircon ages for intracaldera domes at Gölcük (Isparta, Turkey)

- U-Th disequilibrium for zircon and whole rocks from Gölcük volcano were determined.
- Zircon crystallization ages and (U-Th)/He data yielded new eruption age constraints.
- Disequilibrium-corrected (U-Th)/He zircon ages are 14.1 ± 0.5 and 12.9 ± 0.4 ka.
- Gölcük intra-caldera domes coeval and > 10 ka younger than published K-Ar ages.
- Young eruption ages for domes redefine minimum ages for last explosive eruption.

Pleistocene to Quaternary volcanism in the Isparta region (SW Anatolia, Turkey) comprises potassic lavas and pyroclastic deposits, which are largely centered around Gölcük caldera. Trachytic intracaldera lava domes represent the latest eruptive event at Gölcük, and their eruption age is crucial for defining a minimum age for the preceding caldera-forming explosive eruption. Here, we present combined U-Th and (U-Th)/He zircon geochronological data for two intracaldera lava domes constraining their crystallization and eruption ages, respectively. U-Th zircon crystallization ages peak between ca. 15 and 25 ka. In rare instances U-Th zircon crystallization ages date back to ca. 59 and 136 ka. U-Th zircon crystallization ages also permit (U-Th)/He eruption ages from the same crystals to be individually corrected for uranium series decay chain disequilibrium, which is mainly due to the deficit of the intermediate daughter 230Th in zircon. Average disequilibrium-corrected (U-Th)/He zircon ages are 14.1 ± 0.5 and 12.9 ± 0.4 ka (1σ). These ages are indistinguishable within analytical uncertainties suggesting that both lavas erupted quasi simultaneously. This contradicts published K-Ar ages that suggest an extended hiatus from ca. 52 to 24 ka between intracaldera dome eruptions. Evidence for protracted zircon crystallization over several thousands of years prior to eruption indicates the presence of a long-lived magma reservoir underneath Gölcük caldera. Implications of the revised eruptive geochronology presented here include younger ages for the latest effusive eruptions at Gölcük, and potentially also a more recent explosive eruption than previously assumed.