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TitleBorehole heat flow along the eastern flank of the Juan de Fuca Ridge, including effects of anisotropy and temperature dependence of sediment thermal conductivity
AuthorPribnow, D F C; Davis, E E; Fisher, A T
SourceJournal of Geophysical Research vol. 105, no. B6, 2000 p. 13,449-13,456, (Open Access)
Alt SeriesGeological Survey of Canada, Contribution Series 2000135
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region
AreaJuan de Fuca Ridge; Ocean Drilling Program Leg 168; Site 1023; Site 1024; Site 1025; Site 1026; Site 1027; Site 1028; Site 1029; Site 1030/31; Site 1032
Lat/Long WENS-129.5000 -127.5000 48.5000 47.5000
Subjectsgeophysics; marine geology; heat flow; thermal conductivity; anisotropy; oceanic lithosphere; porosity; Juan de Fuca Ridge; Cenozoic
Illustrationssketch maps; cross-sections; plots
Released2000 06 10
AbstractThe thermal conductivities of 15 whole-round sediment samples collected during Ocean Drilling Program (ODP) Leg 168 between 17 and 440 m below the seafloor on the eastern flank of the Juan de Fuca Ridge were tested to document their anisotropy and temperature dependence using the divided bar technique. Tests over a temperature range of 5°C to 60°C reveal variations in conductivity of up to ±15%. The sign and amplitude of these variations depend on the thermal conductivity at laboratory (room) temperature (hrt): if hrt = 0.8 W m-1 K-1 (high porosity), conductivity increases with temperature; if hrt = 1.2 W m-1 K-1 (moderate porosity), conductivity does not change with temperature; if hrt = 1.6 Wm-1K-1 (low porosity), conductivity decreases with temperature. This behavior results from a positive temperature coefficient for seawater (h proportional to T) and a negative coefficient for rock matrix (h proportional to 1/T). A special sampling technique for unconsolidated sediments made it possible to measure horizontal (hHOR) and vertical (hVER) components of thermal conductivity independently and to determine a mean anisotropy value (hHOR/hVER) of 1.2. Corrections, which are <10% for anisotropy and <1% for temperature, were applied using in situ temperatures, shipboard line source thermal conductivities, porosities, and the geometric mean mixing model that accounts for matrix and porewater constituent conductivities. On the basis of these corrected conductivities and a harmonic averaging of values weighted according to the lithologic division of the sediment sections into clay-rich and sand-rich units, values of heat flow estimated from borehole temperature measurements are lower than those previously estimated by <10% except for one site where the section is dominated by sand. Shallow seafloor heat flow measured with gravity-driven probes may also need to be corrected for anisotropy, although the degree of anisotropy in the unconsolidated, high-porosity sediments within a few meters of the seafloor is poorly constrained.