- © The Mineralogical Society Of America
Fluid inclusions in minerals may form in any type of volcanic or plutonic rock ranging from mafic to silicic compositions. Because all igneous rocks reach fluid saturation at some stage during their evolution, fluids trapped as inclusions in magmatic minerals belong to a certain paragenesis or phase assemblage, which may include minerals, melts and one or more fluid phases. These fluid inclusions reflect one or more stages during rock evolution, and can be used to constrain multistage formation and evolution processes including ascent histories, magma chamber processes and crystallization behavior.
Fluid inclusions can provide thermobarometric data on various timescales. During ascent of mafic to intermediate magmas, fluid inclusions may form within hours to days and record transient magma stagnation levels, whereas chemical mineral-melt thermobarometry requires equilibrium mineral growth and thus typically reflects well-defined crystallization events (Roedder and Bodnar 1980; Wanamaker et al. 1990; Hansteen et al. 1998; Klügel et al. 2000; Frezzotti and Peccerillo 2004). Such data has only rarely been combined with melt inclusion investigations in order to depict detailed magma ascent histories (e.g., Bureau et al. 1998). During prolonged crystallization in magma chambers or in the plutonic environment, however, fluid inclusions reflect the equilibrium situation, and data from various thermobarometric methods should overlap.
This chapter focuses on the use of fluid inclusions as thermobarometers to constrain magmatic processes and timescales. After an introduction of basic principles and explanation of the most relevant fluid systems we show in a “cookbook” style how barometric data are derived, and discuss error magnitudes and pitfalls. Thermobarometric information attained from chemical mineral-melt equilibria are compared to that obtained from fluid inclusions in order to provide detailed accounts for magma ascent and crystallization. Although the term “fluid inclusion” is often used in a general way comprising all inclusions that were …