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WITHDRAWN -Comparing hydrothermal responses to eruption on submarine arc volcanoes and mid-ocean ridges.

David A. Butterfield

  • Affiliations: Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington and NOAA/PMEL, Seattle, Washington, USA

  • Presentation type: Talk

  • Presentation time: Tuesday 09:45 - 10:00, Room R290

  • Programme No: 6.2.6

  • Theme 6 > Session 2

Abstract

More than 300 submarine hydrothermal systems have been located and sampled, but there are very few direct observations of hydrothermal activity associated with deep submarine eruptions. Hydrothermal fluids produced by interaction of erupting lava, hot magmatic gases, and seawater have been sampled at NW Rota-1, a basaltic volcano on the Mariana arc, and at West Mata, a boninite volcano in the NE Lau basin. The chemistry of fluids sampled directly over erupting lavas from both sites (pH 1 to 2, high levels of dissolved SO2, Mg concentrations higher than seawater, elevated levels of Fe, Al, and Si, low Li) indicate rapid and short duration acidic attack on freshly erupted lavas by condensed, SO2-rich magmatic gases mixed with seawater. These fluids are unlike the high-temperature fluids produced in the deep subseafloor (near zero Mg, pH 3 to 5, elevated trace alkalies), where conditions approach equilibrium at low water/rock ratios. High-temperature fluids collected on or near freshly erupted basalt in 1991 on the East Pacific Rise have low Mg, low Cl, high H2S, slightly enriched Li, and other characteristics associated with high-temperature reaction of limited duration plus phase separation (Von Damm, 2000). Differences between the hydrothermal response to eruptions on MOR and submarine arc volcanoes can be tentatively attributed to the structure of hydrothermal circulation around dike-driven eruptions with existing high-temperature vents on MORs versus conduit-fed eruptions within more permeable constructional volcanic cones on arcs. Magma redox state also plays a role, producing SO2-rich fluids on arcs and H2S-rich fluids on MORs.