Hydrothermal silica chimney fields in the Galapagos Spreading Center at 86°W

Details Hydrothermal silica chimney fields in the Galapagos Spreading Center at 86°W Hydrothermal silica chimney fields in the Galapagos Spreading Center at 86°W

Aug 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988e%26psl..89..261h&link_type=abstract

Earth and Planetary Science Letters, Volume 89, Issue 3-4, p. 261-272.

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Silica chimneys were discovered in 1985 at 86°W in the rift valley of the Galapagos Spreading Center at 2600 m depth (``Cauliflower Garden''). The inactive chimneys lack any sulfides and consist almost entirely of amorphous silica (up to 96 wt.% SiO2, opal-A); Fe and Mn oxides are minor constituents. Oxygen isotope data show that formation of the silica chimneys took place at temperatures between 32°C (+29.9‰ δ18O) and 42°C (+27.8‰ δ18O). Th/U dating reveals a maximum age of 1440 +/- 300 y. Amorphous silica solubility relations indicate that the silica chimneys were formed by conductive cooling of pure hydrothermal fluids or by conductive cooling of a fluid/seawater mixture. Assuming equilibrium with quartz at 500 bars, initial fluid temperatures of more than 175°C (i.e., a concentration of > 182 ppm SiO2) were required to achieve sufficient supersaturation for the deposition of amorphous silica at 40°C and 260 bars. If the silica chimneys originate from the same or a similar fluid as higher-temperature ( < 300°C) sulfide-silica precipitates found nearby (i.e., 2.5 km away), then subsurface deposition of sulfides may have occurred.
Present address: Institut für Petrographie und Geochemie, Universität Karlsruhe, D-7500 Karlsruhe, F.R.G.

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