The Analysis and Interpretation of Noble Gases in Modern Hydrothermal Systems

Abstract

AbstractThis chapter describes the practice in the analysis and interpretation of noble gases in modern hydrothermal systems, including sample collection and analytical methods, implications of geographical distribution of helium isotopes in the large scale (100–1000 km) and the small scale (1–100 km), temporal variation of helium isotopes in some volcanoes, and the other noble gas isotope and abundance variations in hydrothermal systems. First, details of sampling method of volcanic and hot spring gases are discussed together with characteristics of two types containers, Giggenbach-type and lead-glass. Second, analytical techniques of noble gas abundances by an isotope dilution method using a QMS-based system, and neon interference on helium isotope measurements by a magnetic sector type mass spectrometer are written precisely. Third, helium isotope variations in three modern volcanic regions, such as hot spot, mid-ocean ridge, and subduction zone are compiled and discussed together with geo-tectonic settings and geophysical data. Fourth, across the island arc variations of helium isotopes are described against recent seismic tomography data in Northeast Japan, Southwest Japan, North Island of New Zealand, and Kamchatka peninsula of Russia. Then smaller size of the isotope variations around the independent volcano such as Mt Ontake and Mt. Nevado del Ruiz are discussed. Fifth, temporal variations of helium and neon isotopes in volcanic discharges are discussed with examples showing the effects of changes in volcanic activity on noble gas ratios. Sixth, the isotopic compositions of neon, argon, krypton and xenon isotopes in volcanic and hydrothermal systems is discussed and related to mantle and crustal degassing processes. The last section (seven) provides applications of noble gases to traces sources and crustal contamination processes of more abundant gases such as carbon dioxide, methane and nitrogen with examples from well studied hydrothermal systems in New Zealand, Italy, Central America and Greece. In summary noble gases have a wide range of applications in volcanic and hydrothermal systems and are key indicators of tectonic setting, mantle and magma degassing; they provide valuable information on the current activity of a volcano and in combination with major gases can provide insights to understanding other geologically important volatiles such as carbon dioxide, methane and nitrogen.KeywordsModern Hydrothermal SystemsNoble GasesHelium IsotopesLead-containing GlassesVolcanic FrontThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.