Principal Interest: Geochemical Role of Fluids in the Lithosphere
A large amount of evidence has come to light over recent decades establishing that hot, aqueous solutions containing electrolytes and gases (e.g. CO2, CH4, N2, and H2S) have circulated through the Lithosphere during much of the Earth's history. Such hydrothermal fluids are recognized as having been key agents in redistributing heat and mass, either by direct advective flow or indirectly by catalysing rock deformation and tectonic displacement. Economically significant manifestations of these processes include the formation of metalliferous and rare-element ores, the migration and entrapment of petroleum and gas, and the generation of geothermal energy resources. Many potential hazards are posed by hydrothermal fluids, including the triggering of earthquakes and explosive volcanism, and the leakage of underground repositories of radioactive and toxic chemical waste. Hydrothermal fluids are also integral participants in processes of fundamental geological interest, such as metamorphism, magma generation and migration, and diagenesis.
Research into this broad field is currently concentrating on the following four sub-topics:
1) Fluid Inclusions (see also Fluid Inclusion Laboratory)
Our understanding of past and present hydrothermal fluids, and hence of the processes in which they are involved, draws heavily on analyses of fluid inclusions (micrometer-size cavities in minerals that have encapsulated relics of formerly mobile solutions during mineral growth or deformation). The methodology is still under development, and some of the aspects currently under investigation include:
Systematics of fluid inclusions in minerals
Isochoric behaviour in common compositional types of inclusions (calibrated by synthetic fluid inclusions)
Reequilibration phenomena
Classical and statistical thermodynamic modelling of phase stability in fluid inclusions
Development and improvement of analytical techniques, including microthermometry, Raman spectroscopy, ion-probe analysis (SIMS), and crush-leach analysis for chemical and isotopic components.
2) Physicochemical Properties of Lithospheric Fluids
Reconstructions of past fluid-rock interaction and predictions of future processes require thermodynamic data on the major fluid types of the Lithosphere. To obtain the necessary data, fluid inclusions of known composition and density are being synthesized. Evaluation of the isochoric phase transitions measured in the synthesis products allows phase boundaries and partial molar volumes to be derived.
3) Fluid Generation and Migration in the Lithosphere
Fluids circulating through the Lithosphere have diverse origins and migration mechanisms, and many of these are still poorly known. Thus the origins of fluids in metamorphic and diagenetic rocks are being investigated, based on examination of natural samples, with emphasis on the petrologic controls on fluid chemistry. Fluid flow paths are also being unravelled using geochemical and radiogenic isotope methods.
4) Hydrothermal Ore Deposits
Successful exploration for metallic ore deposits requires an understanding of how the deposits form. Research is currently underway to help understand the genesis of lode-gold deposits in metamorphic belts, using the deposits in the Western Alps as examples. The approach combines field mapping, chemical and isotopic analysis of minerals and fluid inclusions, and thermodynamic modelling of fluid-rock interaction.
Research group Rock-Water Interaction
