There is no doubt that fluids are present in some form during metamorphism of most rocks. It is difficult, however, to obtain the information on metamorphic fluids from a rock because little of the fluids is left in the rock except as volatile components in some minerals. Neither is it possible to sample the fluid during metamorphism except in very limited cases of low-grade metamorphism (=geothermal field). Theoretical calculations using mineral compositions in the rock can give a fluid composition with which the minerals now present in the rock must have been in equilibrium with. However, the amounts of some components in the fluid such as Cl and N cannot easily be obtained by calculations. In addition, there probably were several generations of fluid that have passed through the rock for which the compositions cannot be calculated: only the fluid in equilibrium with the present mineral assemblages can be calculated. The results from such petrological calculations will be compared to the fluid present in small cavities in the minerals in the rock (=fluid inclusions). These fluid inclusions are thought to have trapped fluids that were present in the rock at different times during its metamorphic history. Two small areas, in Texas and south-central Maine, will be studied. The results should tell us whether the fluid inclusions can be used as the samples of unmodified metamorphic fluids in these and other areas. The results should also increase understanding of the nature of the fluid phase and its role during metamorphism and contribute toward a better understanding of metamorphic processes in general.
