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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, B01102, doi:10.1029/2003JB002476, 2004

Hydrothermal seepage patterns above a buried basement ridge, eastern flank of the Juan de Fuca Ridge

G. A. Spinelli

Earth Sciences Department, University of California, Santa Cruz, California, USA


L. Zühlsdorff

Department of Geosciences, University of Bremen, Bremen, Germany


A. T. Fisher

Earth Sciences Department, University of California, Santa Cruz, California, USA


C. G. Wheat

Global Undersea Research Unit, University of Alaska Fairbanks, Fairbanks, Alaska, USA


M. Mottl

Department of Oceanography, University of Hawaii, Hawaii, USA


V. Spieß

Department of Geosciences, University of Bremen, Bremen, Germany


E. R. Giambalvo

Sandia National Laboratories, Carlsbad, New Mexico, USA


Abstract

We use the distributions of sediment physical properties and modeled basement overpressures to estimate the spatial distribution of fluid seepage through sediments over and around the “First Ridge,” a buried basement ridge on the eastern flank of Juan de Fuca Ridge. Fluid discharge rates differ by 1 order of magnitude because of differences in sediment hydraulic properties and by 2 orders of magnitude resulting from differences in sediment thickness and basement overpressure. Sediment type distribution appears to have resulted from differences in local seafloor relief. Compression index (ease of consolidation) increases with proportion of hemipelagic material, from 0.5 at 30% hemipelagic to 1.4 at 95% hemipelagic. Permeability at 50% porosity decreases with proportion of hemipelagic material, from 2 × 10−16 m2 at 30% hemipelagic to 6 × 10−18 m2 at 95% hemipelagic. Modeled seepage rates, derived from basement overpressures and sediment physical properties, range from 0 to 27 mm/yr. The average seepage rate over the entire 11 km of ridge within our study area is 1.3 mm/yr. On the basis of the model results, half of the total volume flux of seepage from the First Ridge is contributed from 25% of the study area, with flow rates ≥1.1 mm/yr. Low seismic reflection amplitude anomalies are generally correlated with areas of high seepage rates.

Received 27 February 2003; accepted 29 September 2003; published 14 January 2004.

Index Terms: 1815 Hydrology: Erosion and sedimentation; 1832 Hydrology: Groundwater transport; 3015 Marine Geology and Geophysics: Heat flow (benthic) and hydrothermal processes; 3022 Marine Geology and Geophysics: Marine sediments—processes and transport; 3025 Marine Geology and Geophysics: Marine seismics (0935).

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Citation: Spinelli, G. A., L. Zühlsdorff, A. T. Fisher, C. G. Wheat, M. Mottl, V. Spieß, and E. R. Giambalvo (2004), Hydrothermal seepage patterns above a buried basement ridge, eastern flank of the Juan de Fuca Ridge, J. Geophys. Res., 109, B01102, doi:10.1029/2003JB002476.