- © The Mineralogical Society Of America
Epidote minerals (the epidote group together with the orthorhombic polymorph zoisite) occur in a wide range of igneous, metamorphic and sedimentary lithologies. Although often present in only small quantities, epidote group minerals can nonetheless be used to generate important quantitative constraints on processes such as regional metamorphism, deep-seated pluton emplacement and uplift, hydrothermal fluid flow, and sedimentary provenance (e.g., Zen and Hammarstrom 1984; Brandon et al. 1996; Cartwright et al. 1996; Keane and Morrison 1997; Spiegel et al. 2002). Petrologic studies on epidote group minerals formed by these and other processes are reviewed in Bird and Spieler (2004), Grapes and Hoskin (2004), Enami et al. (2004), and Schmidt and Poli (2004). In this chapter, stable and radiogenic isotope studies of epidote group minerals will be reviewed. Although stable and/or radiogenic isotope data exist for epidote group minerals from a number of different geologic settings, such data have produced particularly important insights into 1) fluid flow associated with variable grades of metamorphism, particularly ultra-high-pressure (UHP) metamorphism, 2) intrusion of deep-seated plutonic systems, 3) the nature of hydrothermal alteration in geothermal systems, 4) age relations in hydrothermal systems, and 5) sedimentary provenance.
STABLE ISOTOPE SYSTEMATICS
Based on the chemical composition of naturally occurring epidote minerals, oxygen, hydrogen, and chlorine stable isotopes all have the potential to be important petrogenetic indicators in systems involving epidote minerals. Oxygen is present in epidote minerals bound in isolated TO4 tetrahedra, T2O7 groups, and in the hydroxyl site as both OH− and O−2. Hydrogen and chlorine are present in the hydroxyl site as OH− and Cl−, respectively, although Cl− is present in only very small quantities (Frei et al. 2004). To date, oxygen and hydrogen isotope systematics have been studied both …