Hydrothermal Vents Along the Spike Segment of the Southern EPR (17 15-40'S)

1997 American Geophysical Union Fall Meeting

J M Hobson, R M Haymon, S M White, S R Baron, P J Sharfstein, K C Macdonald (UCSB, Santa Barbara, CA, 93106)

D.J. Wright (Dept. of Geosciences, Oregon State University, Corvallis, OR 97331-5506)

D Scheirer (Geological Sciences, Brown U., Providence, RI 02912)

In Nov., 1996, near-bottom photographic and acoustic surveys were conducted with the Argo II and DSL-120 kHz sonar systems to study spatial distributions of small-scale features along the axial zone of the ultrafast-spreading (15 cm/yr) southern EPR. The main survey area, called the "Spike Survey", is centered along strike at 17 24'-27'S, where 1991 seismic data show a narrow spike of low-velocity material intruding upward at least 500 m to within 800 m of the seafloor (Detrick et al., 1993). We were especially interested in the distribution of hydrothermal sites in response to along-strike gradients in axial structure and magma supply created by the narrowly focused magma cupola.

Within the Spike Survey we located 14 active high-T sites with black- or white-smoker chimneys, plus 17 additional sites where black or white smoke plumes were present, for a total of 31 high-T sites along a 48 km length of the EPR. By comparison, a 1989 Argo I survey of the fast-spreading (11 cm/yr) EPR at 9 30'-54'N revealed 25 sites with smokers or smoke along a 44 km length of ridge axis (Haymon et al., 1991). Many more inactive chimneys were observed at 9 -10 N than in the Spike Survey area, suggesting that more frequent or recently extensive axial eruptions have destroyed or buried inactive chimneys along the Spike ridge segment. Chimneys in the Spike Area tend to be isolated, small structures, with no more than 5 spindly spires, indicating ages of less than a few years (based on chimney growth rates after the 1991 eruption at EPR 9 45'-52'N).

Vents and animal communities are grouped into 3 fields, each ~9 km in length, and separated by ~7 km-long gaps. Their distribution and dimensions may reflect 4th order ridge segmentation and the pattern of shallow axial magma supply. Animal communities and active vents are not symmetrically dispersed about the magma cupola, but rather are more abundant along strike to the south. Some black smokers are not associated with visible vent fauna. The locations of some, but not all, of the smokers are controlled by identifiable eruptive fissures.

Return to Dawn's Vita