Unveiling Tatun volcanic plumbing structure induced by post-collisional extension of Taiwan mountain belt

Abstract

The Tatun Volcanic Group (TVG) is proximal to the metropolis of Taipei City (population of ca. 7 million) and has long been a major concern due to the potential risks from volcanic activity to the population and critical infrastructure. While the TVG has been previously considered a dormant or extinct volcano, recent evidence suggests a much younger age of the last eruption event (~ 6000 years) and possible existence of a magma reservoir beneath the TVG. However, the location, dimension, and detailed geometry of the magma reservoir and plumbing system remains largely unknown. To examine the TVG volcanic plumbing structure in detail, the local P-wave travel time data and the teleseismic waveform data from a new island-wide Formosa Array Project are combined for a 3D tomographic joint inversion. The new model reveals a magma reservoir with a notable P-wave velocity reduction of 19% (ca. ~ 19% melt fraction) at 8–20 km beneath eastern TVG and with possible northward extension to a shallower depth near where active submarine volcanoes that have been detected. Enhanced tomographic images also reveal sporadic magmatic intrusion/underplating in the lower crust of Husehshan Range and northern Taiwan. These findings suggest an active volcanic plumbing system induced by post-collisional extension associated with the collapse of the orogen.

Unveiling attenuation structures in the northern Taiwan volcanic zone

“…3). Interestingly, previous travel-time tomographic studies have consistently reported high-velocity anomalies in the same region 12,31 . The coexistence of these high-V and high-Q anomalies suggests a potential correlation with the exhumation of metamorphic slate and argillite belts during the mountain-building process.…”

“…While we acknowledge the possibility that low- Q anomalies could be attributed to strong scattering attenuation, as observed in other volcanic regions 68 , 69 , a recent waveform modeling study 46 supports the hypothesis of active hydrothermal events in the TVG region favoring fluid-related contributions. Moreover, the existence of a magma reservoir beneath the TVG region remains plausible but may be situated at greater depths, as suggested by recent tomographic investigations 12 . These deeper magma reservoirs could serve as potential heat sources for the shallower hydrothermal system.…”

“…Conversely, a smaller C value indicates a lower overall Q value, suggesting that the predominant medium in the region is likely composed of softer materials. In this study, we compared our attenuation model with the latest P -wave 12 and S -wave 3-D velocity models 34 in northern Taiwan (Fig. 5 ) for three layers at depths of 0–5 km, 6–10 km, and 11–15 km.…”

“…The existence of a magma chamber beneath the TVG was initially challenged in a seismic waveform study 11 . Nevertheless, subsequent confirmation was provided by a P -wave tomographic model, pinpointing the magma chamber's location at a depth of 8–20 km beneath the eastern part of the TVG 12 .…”

High‐Resolution 3‐D Shear Wave Velocity Model of Northern Taiwan via Bayesian Joint Inversion of Rayleigh Wave Ellipticity and Phase Velocity With Formosa Array

“…This slow anomaly might be related to the magmatic structure of the TVG. Few recent studies have presented evidence indicating the presence of a mid‐crustal magma body associated with the Tatun Volcano (Huang et al., 2021; Lin, 2016). The relative shallow slow anomaly we observed might be related to the remnant magmatic materials left from previous eruptions, or part of the still active magmatic system.…”