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Seafloor eruptions and evolution of hydrothermal fluid chemistry

D. A. Butterfield,1 I. R. Jonasson,2 G. J. Massoth,3 R. A.Feely,3 K. K Roe,1 R. E. Embley,4 J. F. Holden,5 R. E. McDuff,5 M. D. Lilley,5 and J. R. Delaney

1Joint Institute for the Study of Atmosphere and Ocean, University of Washington, Seattle, WA 98195
2Geological Survey of Canada, Ottawa, Ontario, Canada
3Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA 98115
4Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Newport, OR 97365
5School of Oceanography, University of Washington, Seattle, WA 98195

Philosophical Transactions of the Royal Society of London A 355, 369-386 (1997).
Copyright ©1997 by the Royal Society. Further electronic distribution is not allowed.

2. Description of CoAxial site

A seafloor volcanic event was detected by the US Navy SOSUS array beginning near 46°15N, 129°51W on 26 June 1993 and ending near 46°32N, 129°35W on about 16 July 1993 (Dziak et al. 1995; Fox et al. 1995). In July and August 1993, the Canadian remotely operated vehicle ROPOS was deployed from the NOAA ship Discoverer to explore and sample the area affected by the seafloor eruption (Embley et al. 1995) (figure 1). Three event plumes were found in July 1993 (Baker et al. 1995). Given the locations and approximate ages of the plumes (Baker et al. 1995; Massoth et al. 1995) and the prevailing current speed and direction (Cannon et al. 1995), it is likely that all three event plumes originated near the Flow site during the seismically active period. We were able to obtain one pair of titanium major samples during ROPOS dive 234 on 1 August (approximately 2 weeks after the end of the volcanic event) from a 22°C vent at the lava Flow site (marker P1, 46°31.42N, 129°34.85W; a 51°C vent was found later on the same dive). Two more venting areas (Floc site centered near 46°18N, 129°42.5W, and Source site centred near 46°9.3N, 129°48.6W, which is ca. 10 km to the SSE of the initial event swarms) were found and many additional seafloor vent fluid samples were obtained with Alvin in October 1993, July 1994 and July 1995 to provide time series data on temperature and fluid chemistry. A multidisciplinary collection of papers describes some of the initial results of research on the CoAxial segment (Fox 1995).

Figure 1: Map of CoAxial area, showing regional setting (inset bottom), location of lava Flow site, Floc site, and Source site. Circles are event plumes labelled A, B and C in order of both discovery and increasing age at the time of sampling (Baker et al. 1995; Massoth et al. 1995). Arrows show current direction at 1800 m depth (Cannon et al. 1995). A detailed map of the Floc site (inset top) shows the location of markers referred to in the text. Bathymetric contour interval is 200 m.


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