| Title | Hydrothermal venting and geothermal heating in Cascadia Basin |
| Author | Thomson, R E; Davis, E E; Burd, B J |
| Source | Journal of Geophysical Research, Solid Earth vol. 100, no. B4, 1995 p. 6121-6141, https://doi.org/10.1029/95jb00030 |
| Year | 1995 |
| Alt Series | Geological Survey of Canada, Contribution Series 47594 |
| Publisher | Wiley-Blackwell |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Western offshore region |
| Lat/Long WENS | -130.0000 -120.0000 50.0000 40.0000 |
| Subjects | marine geology; tectonics; submarine hydrothermal vents; hydrothermal systems; heat flow; heat conduction; igneous rocks; basins; water temperature; geothermal temperatures; Cascadia Basin; Cascadia
Subduction Zone; Blanco Transform; Gorda Ridge |
| Illustrations | location maps; graphs |
| Released | 2012 09 20 |
| Abstract | Observations in Cascadia Basin on the eastern flank of the northern Juan de Fuca Ridge reveal significant bottom water modification as a result of regional conductive heating and local hydrothermal
venting. Seafloor conductive heating occurs throughout the sedimented basin while hydrothermal fluid discharge is confined to small (1 km2) isolated igneous basement outcrops. In the northern sector of the plateaulike basin, the vertical fluxes of
heat and mass associated with these seafloor processes lead to the formation of a 250- to 350-m-thick "geothermal boundary layer" characterized by anomalously high temperature, reduced vertical stability, and high dissolved silicate concentration.
Using a basinwide average lithospheric heat flux of 0.3 W m-2 and the observed thermal anomaly structure of the water column, we obtain a mean residence time of 1 to 2 years for the deep water over Cascadia Basin. Detailed water property data
collected in 1992 and 1993 within the immediate vicinity of three isolated igneous basement outcrops in the north-central sector of the basin indicate that local bottom-water heating arises from low-temperature venting through the summit and flanks
of the outcrops. Near the smallest edifice, especially well-defined layers of anomalously warm, particle-laden water were found within ±20 m of the outcrop summit depth of 2610 m. Maximum anomalies of temperature, light attenuation coefficient, and
dissolved silicate concentration in the layers were 0.040°C, 0.015 m-1, and 5 umol L-1, respectively. We estimate the local heat flux, Fo' from the smallest outcrop to be (2.4±0.8)U × 109 W, where U (m s-1) is the mean horizontal current at the
venting depth. For reasonable mean currents in the range 10-3 to 10-2 m s-1, we find Fo' ? 0.2 to 2.4 × 107 W. Assuming that the depressed conductive heat flow of -0.05 W m-2 observed through the sedimented seafloor surrounding the smallest outcrop
reflects the advective loss of heat through the outcrop, the radial distance over which crustal fluids must collect heat and converge on the outcrop is about 10 km. |
| GEOSCAN ID | 204571 |
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