Hydrogeology of the Juan de Fuca Ridge - implications from downhole logging and petrophysical core data

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Integrated Ocean Drilling Program Leg 300 plans investigate the hydrogeological situation at the eastern flank of the Juan de Fuca Ridge by deep drilling into the oceanic crust, crosshole experiments, and long-term observations. The objectives of this research proposal are to use geophysical measurements from boreholes (well-logging data) and from core samples from Leg 300 boreholes to study (1) the relation between hydrogeology and the basement architecture at the eastern flank of Juan de Fuca Ridge and (2) the effect of circulation of seawater through the crust on the physical properties of the rocks. The continuous physical information from the well-logging data will be used to reconstruct the volcanic architecture of the drill holes in order to obtain continuous lithological profiles that are not biased by gaps due to an expected high core loss. The continuous reconstructed profiles will be used to map and quantify the occurring lava morphologies... and to identify possible aquifer horizons and their relation to the eruption history at the drill site. Comparison of petrophysical data from the Leg 300 boreholes and other already existing boreholes into oceanic crust will reveal the effect of hydrothermal alteration and ageing of oceanic crust con the physical properties of the crust.