Hydrothermal system in the Tatun Volcano Group, northern Taiwan, inferred from crustal resistivity structure by audio-magnetotellurics

Shogo Komori,Hsieh-Tang Chiang,Wataru Kanda,Ryokei Yoshimura,Hiroyuki Inoue,Chang-Hwa Chen,Benjamin Fong Chao,Mitsuru Utsugi,Tsuneomi Kagiyama

doi:10.1186/s40645-014-0020-7

Abstract

The present study proposes an improved conceptual model for the hydrothermal system in the Tatun Volcano Group in northern Taiwan. In the study, audio-magnetotellurics (AMT) surveys were conducted to reveal the spatial distribution of resistivity, which is highly sensitive to fluids and hydrothermal alteration. By combining the obtained resistivity structure with other geophysical and geochemical evidence, the following hydrothermal system was inferred. Beneath Chishinshan, vapor-dominant hydrothermal fluids, supplied from a deeper part, are maintained in a low to relatively low resistivity region (5 to 20 Ω m) that is covered by a clay-rich cap, represented by an upper extremely low resistivity layer. Fluid ascent is suggested by a pressure source and clustered seismicity. Exsolved gases result in fumarolic areas, such as Siao-you-keng, while mixing of gases with shallow groundwater forms a shallow flow system of hydrothermal fluids in the Matsao area, represented by a region of less than 10 Ω m. The fumarole in the Da-you-keng area originates from vapor-dominant hydrothermal fluids that may be supplied from a deeper part beneath Cing-tian-gang, suggested by a pressure source and low to relatively low resistivity. Horizontally extended vapor-bearing regions also suggest the possibility of future phreatic eruptions. The proposed conceptual model may provide clues to detecting precursors of potential volcanic activity.

Highlights

The Tatun Volcano Group (TVG) covers an area of approximately 300 km2 on the northern tip of the island of Taiwan, only about 10 km north of the capital city of Taipei
Electromagnetic studies at the TVG The magnetotellurics (MT) principle (e.g., Cagniard 1953; Vozoff 1991; Simpson and Bahr 2005) is based on electromagnetic induction and has been widely used at hydrothermal and volcanic areas for estimating the crustal electric resistivity structures associated with their activity
The present study will show the shallow crustal resistivity structure associated with the intense hydrothermal activity in the TVG in northern Taiwan

Summary

Introduction

The Tatun Volcano Group (TVG) covers an area of approximately 300 km on the northern tip of the island of Taiwan, only about 10 km north of the capital city of Taipei. Many studies to date have found resistivity anomalies corresponding to the paths and phase states of hydrothermal fluids, and to the fluid-bearing structure in volcanic and geothermal areas (e.g., Ogawa et al 1998; Kanda et al 2008; Aizawa et al 2009; Komori et al 2010, 2013a; Revil et al 2011). Resistivity anomalies may provide critical constraints leading to better models of hydrothermal systems. The present study proposes an integrated hydrothermal model that combines newly revealed electric resistivity structures of the crust with geophysical and geochemical evidence. We discuss implications for potential future phreatic eruptions for the TVG

Results

Discussion

Conclusion