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Fluid behaviour in the upper crystalline crust : a multidisciplinary approach

Exploitable results

The project aimed to improve the understanding of fluid behaviour in the upper continental crust (i.e. the upper crystalline 10 km) by comparing modern fluid flows with fossil fluid flows. It also aimed to establish the conditions under which fluids are present in the upper crust, and to investigate their source. The project would pay particular attention to the relationship between tectonics and crustal fluids, and the role of fluids in heat and mass transfer. When crystals grow from fluids deep in the crust, small amounts of water or other fluids can become trapped. By studying these "fluid inclusions" in crystalline rocks (e.g. in mineral veins), from a number of stable crustal areas, scientists are able to determine certain characteristics relating to particular host rocks. This enables them to better understand the nature of fluid flows in crystalline rocks, which in turn can be applied either in the exploitation of geothermal waters or in other geological disciplines. Until now, geologists have found discrepancies between geophysical and petrological interpretations of the importance of fluid in crystalline rocks. By combining the study of palaeofluids with geochemical modelling, the project attempted to reduce this knowledge gap. Specific objectives of the project included: determining the chemical composition of crustal fluids at different times; investigating flow patterns in the upper continental crust, particularly in the role of fluid overpressures; and identifying the extent to which fluid-related features in ancient rocks either reflect continuous fluid processes or a series of distinct events.