Characteristics and Origins of Hot Springs in the Tatun Volcano Group in Northern Taiwan

Abstract

This paper systematically surveyed distribution and field occurrences of 13 hot springs as well as geochemical investigation on the geothermal area of the Tatun Volcano Group (TVG). According to Piper diagrams, pH values, field occurrences and water-rock interactions, these hot springs can be classified into three types: (1) Type I, SO₄^2- acidic water where the reservoir is located in the Wuchishan Formation; (2) Type II, HCO₃^- a near neutral spring where waters originate from the volcanic terrane (andesite); and (3) Type III, Cl^- -rich acidic water where waters emanate from shallower Wuchishan Formation. In terms of isotopic ratio, δD and δ¹⁸O values, two groups of hot spring can be recognized. One is far away from the meteoric water line of the Tatun area with values ranging between -26.2‰ and -3.5‰, and from -3.2‰ to 1.6‰, respectively. However, another close to the meteoric water line of the Tatun area is between -28.4‰ and -13.6‰, and from -5.5‰ to -4.2‰, respectively. In addition, the δ³⁴S value of thermal waters can also be distinguished into two groups, one ranging from 26.1‰ to 28.5‰, and the other between 0.8‰ and 7.8‰. Based on field occurrences and geochemical characteristics, a model has been proposed to illustrate the origin of these hot springs.