Review of the systematics of CO2-H2O fluid inclusions

Aqueous solutions that contain volatile (gas) components are one of the mos t important types of fluid in the Earth's crust. The record that such fluid s have left in the form of fluid inclusions in minerals provides a wealth o f insight into the geochemical and petrologic processes in which the fluids participated. This article reviews the systematics of CO2-H2O fluid inclus ions as a starting point for interpreting the chemically more complex syste ms. The phase relations of the binary are described with respect to a quali tative P-T-X model, and isoplethic-isochoric paths through this model are u sed to explain the equilibrium and non-equilibrium behaviour of fluid inclu sions during microthermometric heating and cooling. The P-T-X framework is then used to discuss the various modes of fluid inclusion entrapment, and h ow the resulting assemblage textures can be used to interpret the P-T condi tions, phase states, and evolution paths of the parent solutions. Finally, quantitative methods are reviewed by which bulk molar volume and compositio n of CO2-H2O fluid inclusions can be determined from microthermometric obse rvations of phase transitions. (C) 2001 Elsevier Science B.V. All rights re served.