Eruptive history of Mt Huangzuei, Eastern Tatun Volcano Group, Taiwan, resolved by ⁴⁰Ar/³⁹Ar and zircon double-dating of lava flows

The Tatun Volcano Group (TVG), located within the Northern Taiwan Volcanic Zone, formed in an extensional back-arc setting at the western end of the Ryukyu subduction system. Although recent studies suggest that the TVG is significantly younger than previously thought, the scarcity of reliable geochronological data on its eruptions continues to impede efforts to reconstruct its eruptive history. In this study, we employed high-precision ⁴⁰Ar/³⁹Ar dating of plagioclase and groundmass, alongside with combined U–Th disequilibrium and (U–Th)/He dating of zircon, to constrain eruption ages of andesitic lava flows from Mt. Huangzuei in the eastern TVG. Our integrated dataset reveals at least four distinct eruptive phases: Stage I (c. 141 ka) produced the most voluminous lava flows to the northeast and east; Stage II (c. 107 ka) was marked by dome formation; Stages III (c. 90 ka) and IV (< 70 ka) represent progressively younger, north-directed lava effusion. Zircon crystallization ages constrained by U–Th disequilibrium dating exhibit distinct clusters, some of which are overlapping with eruption ages, suggesting short magmatic residence times prior to the c. 141 ka and c. 107 ka eruption events. Additionally, a pooled crystallization age cluster of c. 200 ka may indicate a previously undocumented eruptive phase, warranting further investigation of older deposits. These findings refine the eruptive chronology of the TVG and underscore the need for expanded geochronological coverage to better constrain eruption dynamics and inform regional volcanic hazard models.