altimetry of the new data will allow accurate estimates of 

 organism densities to be computed from abundance counts. 



A MODEL FOR THE ASHES HYDROTHERMAL VENT SYSTEM 



This preliminary survey shows that the total volume and 

 number of sulfide chimneys within Ashes Vent Field is small 

 compared to other vent fields along the mid-ocean ridge, such as 

 the Explorer Ridge ( Tivey and Delaney, 1986), southern Juan de 

 Fuca (Normark et al . , 1987), Galapagos (Malahoff, 1985), and 

 segments of the East Pacific Rise ( Spiess et al., 1980). The 

 CASM Vent Field at the northern end of Axial Volcano's summit 

 caldera is also small, in comparison. It is possible that 

 frequent volcanic activity within the summit caldera of the 

 volcano prohibits the formation of extensive surficial sulfide 

 deposits by regularly covering successive sulfide structures with 

 fresh lava flows. Large deposits, however, may still be 

 precipitating beneath the surface. Previous research has 

 indicated that larger deposits are probably formed as a result of 

 multiple hydrothermal cycles (Lowell and Rona, 1985). Given such 

 a model system, surficial hydrothermal vent fields would be 

 underlain by an inter-layered series of prior hydrothermal 

 deposits and lava flows, all formed along the same major fault 

 system. The unusually high gold content of the sulfide chimney 

 suggests secondary enrichment, a process that would be 

 facilitated by hydrothermal fluid leaching old sulfide deposits 

 during convective circulation. 



Results of the current study suggest that regional 

 topography channels mixing vent water along the strike of the 

 faults that form the walls of the volcano's summit caldera, 

 affecting the pattern of sedimentation in the vent field. 

 Organism distributions are explained, in part, by local geology 

 and by vent processes. Regional tectonics control the 

 emplacement of polymetallic sulfide deposits and the nature and 

 distribution of diffuse warm water seepage. Observed zonation 

 attributable to hydrothermal vent processes occurs on a wide 

 range of scales, from individual mineral grains in sulfide 

 samples to the biogeography of vent and nonvent organisms at a 

 single vent field; chemical and mineralogical zonation is even 

 evident on a small regional scale, as hydrothermal imprints 

 preserved in the local sedimentary record. 



This paper is Hawaii Institute of Geophysics Contribution 

 No. 2051. 



REFERENCES 



Arquit, A. M. , A. Malahoff, and G. M. McMurtry, 1985. Chemical 

 and biological halos of a hydrothermal vent system, Axial 

 Caldera, Juan de Fuca Ridge. EOS , Vol. 66, No. 18, p. 401 

 (Abstract ) . 



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