Surprisingly young age for Chihsingshan in Taipei

Abstract

The Tatun Volcano Group (TVG), including more than twenty Quaternary volcanoes, is located 15 km north of Taipei, Taiwan. Prior to the late 1990s, the Tatun Volcano Group was considered an extinct or dormant feature based on the absence of historical evidence for eruptions and outdated dating methods. However, recent geochemical and geophysical studies indicated that the magma reservoir beneath the TVG is existing and the possibility of future eruptions is high. Most recently, a U/Pb age study suggested that the TVG magmatism was initiated around 3 Ma but more active ≤ 0.8 Ma with a flare up ≤ 0.35 Ma. Here, we systematically collected fresh andesite samples from the Tatun Volcano Group and dated these samples by using high-precision 40Ar/39Ar technique. Our preliminary study for one sample collected from Chihsingshan, the highest mountain of this area, yielded an age of 86 ± 4 ka (2 sigma errors). This study, for the first time, provided a precise age for the lava flow in the TVG. Our result refuted the widely accepted age model for the Tatun Volcano Group and suggested that the eruption history should be re-appraised. [This study is supported by HKU Science Faculty RAE Improvement Fund.]