Late quaternary eruption history of the Tatun Volcano Group (Taiwan) – new constraints from zircon double-dating and40Ar/39Ar dating of lava flows in Mt. Shamao

Growing evidence for an active magmatic system beneath the Tatun Volcano Group (TVG) in northern Taiwan has heightened efforts to understand its eruption history. Accurately constraining the timing of past eruptions is essential for evaluating volcanic hazards, particularly given the TVG's proximity to the densely populated Taipei metropolitan area. However, previous studies have yielded inconsistent results, underscoring the need for robust and reliable geochronological methods. This study aims to constrain the age and eruption history of the Shamao lava dome, which is considered the youngest eruptive product in the TVG, by applying a zircon double-dating approach that combines UTh disequilibrium and (UTh)/He methods, alongside high-precision 40Ar/39Ar groundmass dating. Zircon UTh disequilibrium data constrain the maximum eruption age of Mt. Shamao to 16.3 ± 1.2 ka and reveal both protracted crystallization of zircon spanning ca. 200 ka and distinct age clusters at ca. 23, 60, and 117 ka, with some grains in secular equilibrium (>300 ka). These older populations coincide with other magmatic events in the TVG, suggesting zircon inheritance or the tapping of a long-lived, interconnected magma reservoir with episodic pulses. Zircon (UTh)/He dating yields a late Pleistocene eruption age of 16.3 ± 4.9 ka, consistent with a new groundmass 40Ar/39Ar plateau age of 15.0 ± 6.3 ka and previously reported radiocarbon ages indicating eruptive activity between ca. 23 and 13 ka. These results challenge earlier interpretations of Holocene volcanism in Mt. Shamao (i.e. at 1.3 ka) and highlight the reliability of integrated geochronological techniques for dating young volcanic rocks. While additional data are required to refine eruption recurrence models, this study provides a critical foundation for improving volcanic hazard assessments and risk mitigation strategies in northern Taiwan.