Hydrogeology of the Juan de Fuca Ridge - implications from downhole logging and petrophysical core data
Final Report Abstract
Integrated Ocean Drilling Program Expedition 301 drilled four holes at one location of the Juan de Fuca Ridge to study the hydrogeological situation at the eastern flank of Juan de Fuca Ridge. Downhole wireline logs from the basaltic basement, basah core samples and sediment whole round samples were analyzed in this research project to explore the controlling effect of basement architecture on the fluid circulation through the crust, to investigate the effect of this circulation on the physical properties of the rocks and to study the hydraulic properties of the sediments. Downhole wireline logs and results of petrophysical measurements on basaltic core samples were compared with data from other boreholes drilled into upper oceanic crust of different age with Site U1301B representing the youngest of these holes. This comparison shows that the larger scale wireline measurements from Hole U301B are consistent with values expected for young oceanic crust and indicate a modest alteration of the crust. In contrast, core-scale physical properties from Hole U130IB do not show the expected values for young crust but show typical values of older, stronger altered crust. These observations are likely related to the specific geological situation at the drill site. Until relatively recently, basement outcrops around Site U1301 were exposed to the seafloor. Until most of the exposed basement in this area was buried, hydrothermal circulation extracted much of the lithospheric heat, kept basement fluid temperatures low, and limited the rate and extent of alteration; a subsequent period of highertemperature fluid circulation with more restricted and less oxidative conditions resulted in enhanced and pervasive aheration of crustal rocks. Sediment samples selected for this study are predominantly silty (57 - 96%) with clay being another important constituent. Permeability does not show a significant trend with depth nor with any of the measured physical properties (porosity, density). Vertical permeability decreases with increasing clay content (or decreasing sill content). Horizontal permeability shows less variation in value range than vertical permeabitliy and does not show a significant trend with grain size. No pronounced permeability anisotropy was observed, possibly because sub-samples used to measure vertical and horizontal permeability were not identical and fine layering and laminations observed in the sediments from the Juan de Fuca Ridge may cause differences in composition and physical properties even on the scale of a whole round sample (15 cm).
Publications
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2005. Fahrtbericht zu IODP Expedition 301: Juan de Fuca Hydrogeology. Gemeinsames Kolloquium der DFG-Schwerpunktprogramme "Integrated Ocean Drilling Program " und "Internationales Kontinentales Bohrprogram - ICDP" in Potsdam, 14.-16. März 2005
Bartetzko, A., Heuer, V., Engelen, B.
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2005. Hydrogeology of the Juan de Fuca Ridge - First results from downhole logging and petrophysical core data. Gemeinsames Kolloquium der DFG-Schwepunktprogramme "Integrated Ocean Drilling Program" und "Internationales Kontinentales Bohrprogram - ICDP" in Potsdam, 14.-16. März 2005
Bartetzko, A.
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2005. Link Between Volcanic Architecture and Hydrogeology at the Juan de Fuca Ridge - First results from Hole U1301B (IODP Expedition 301). AGU Fall Meeting 2005
Bartetzko A., Iturrino, G., Tsuji, and Fisher, A.
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2005. Volcanic architecture and hydrogeology at the Juan de Fuca Ridge - First results from downhole logging in Hole U1301B (IODP Expedition 301). FKPE-Arbeitsgruppe Bohrlochgeophysik und Gesteinsphysik, 8. Kolloquium in Hamburg, 21./22. Oktober 2005
Bartetzko, A.
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2006. Hydrothermal alteration in young oceanic crust at Juan de Fuca Ridge - Evidence from downhole logging data (extended abstract). Gerneinsames Kolloquium der DFG-Schwepunktprogramme "Integrated Ocean Drilling Program" und "Internationales Kontinentales Bohrprogram - ICDP" in Greifswald, 27.-29. März 2006
Bartetzko, A.
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2006. Hydrothermal alteration in young oceanic crust at Juan de Fuca Ridge - Evidence from downhole logging data. 66. Jahrestagung der Deutschen Geophysikalischen Gesellschaft in Bremen, März 2006
Bartetzko, A.
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(2008). Physical properties of young (3.5 Ma) oceanic crust from the eastern flank of the Juan de Fuca Ridge: Comparison of wireline and core measurements with global data. J. Geophys. Res., 113, B05105,
Bartetzko, A., and A. T. Fisher
