Heat Flow Evidence for Hydrothermal Circulation in Oceanic Crust Offshore Grays Harbor, Washington

Abstract

Abstract We report 30 new conductive heat flow measurements collected on the Juan de Fuca plate, offshore of Grays Harbor, Washington, just seaward of the deformation front. The data were collected along Cascadia Open‐Access Seismic Transect Lines 4 and 5. A prominent basement high associated with a rift propagation pseudofault is imaged near the western end of Line 4. Lithospheric conductive cooling models, for 9 Ma oceanic crust, predict that heat flow should be ~175 mW m−2. Just seaward of the deformation front heat flow values corrected for the impact of sedimentation are ~200 mW m−2 and rapidly rise to a value of ~750 mW m−2 over the basement high. We find that (1) hydrothermal circulation redistributes heat in the Juan de Fuca plate offshore Grays Harbor, (2) heat in addition to the basal heat flux is required to fit the data, and (3) this heat likely results from a combination of fluid flow associated from ongoing hydrothermal circulation within the subducted oceanic crust and possibly with the pseudofault. Our data and modeling support previous inferences that hydrothermal circulation within the subducting oceanic crust plays an important control on plate interface temperatures.

Keywords

• heat flow
• fluid flow
• Cascadia