Hydrothermal systems associated with regional metamorphism and crustal anatexis; example from the Pyrenees, France
Our understanding of the transport of fluids through the deeper parts of the crust, and in particular through rocks undergoing prograde regional metamorphism, is at an embryonic stage. This stems largely from the difficulty of making direct observations of such processes, in contrast to the situation in active shallow hydrothermal systems (which are accessible to study in boreholes). Stable isotope (^(18)O/^(16)O, ^(13)C/^(12)C, and D/H) studies of metamorphic and igneous rocks and minerals may, however, be used to place constraints on the passage of H_2O- and CO_2-rich fluids through the crust. Oxygen, hydrogen, and carbon are major constituents of both rocks and typical crustal fluids, and these three elements show systematic differences in isotopic composition in the different terrestrial reservoirs.