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GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 11, PAGES 1311–1314, 1997

The Permeability of Young Oceanic Crust East of Juan de Fuca Ridge Determined Using Borehole Thermal Measurements

A. T. Fisher

Earth Sciences Department and Institute of Tectonics, University of California, Santa Cruz

K. Becker

Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

E. E. Davis

Pacific Geoscience Center, Geological Survey of Canada, Sidney, British Columbia

Abstract

Temperature measurements made in Ocean Drilling Program (ODP) Hole 1026B, drilled into a sediment-buried basement ridge in 3.5 m.y. old crust on the eastern flank of Juan de Fuca Ridge, revealed fluid flow from the formation and into the overlying ocean. This flow indicates that the upper basaltic crust at this site is naturally overpressured relative to hydrostatic. This finding is consistent with output from previously published numerical models of hydrothermal circulation in the upper crust that include appropriate crustal geometry, sediment thickness, and basal heat flow. The fluid flowing into Hole 1026B enters the hole through the upper 10 m of basalt below the sediment-basement contact. The flow rate estimated from the thermal data (80-120 m/hr), in combination with the inferred basement overpressure relative to hydrostatic (about 20-30 kPa), was used to estimate the bulk permeability of the shallowest oceanic crust: 5 to 9 × 10⁻¹² m². Such high bulk permeability would allow regionally significant hydrothermal circulation, consistent with thermal homogenization of upper basement in this area.

Received 17 January 1997; accepted 29 April 1997.

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Citation: Fisher, A. T., K. Becker, and E. E. Davis (1997), The Permeability of Young Oceanic Crust East of Juan de Fuca Ridge Determined Using Borehole Thermal Measurements, Geophys. Res. Lett., 24(11), 1311–1314.

Copyright 1997 by the American Geophysical Union.