periodically assessed at sea using a field temperature calibrator. 

 Temperature offsets within the 0° to 400°C calibration range were 

 never greater than 2.0°C. 



RESULTS 



The chemical data determined from vent fluids collected in 

 the titanium samplers are given in Table 2. Endmembers (estimated 

 by extrapolation to "0" Mg along linear element :Mg mixing lines) 

 for the respective analytes at Axial Volcano and for several other 

 sediment-starved ridgecrest spreading center sites are also given. 

 Graphic representations of the Axial Volcano Cl:Mg, H^SrMg and 

 Mn:Mg, Fe:Mg, and Fe:Mn relations are shown in Figures 3 and 4, 

 respectively. Also shown in these figures are the data determined 

 from water samples collected with the PISCES slurp gun (not given 

 in Table 2). Because of sample mixing problems, the slurp gun 

 data were not as reliable as that from the titanium samplers, and, 

 hence, were not used in the determinations of endmembers. 



Venting fluids at Inferno were collected exclusively from the 

 basal outlet discharging the clear fluids described previously. 

 Local currents combined with the single manipulator configuration 

 of Pisces to preclude vent fluid collection from orifices beyond 

 the reach of a bottom-anchored submersible. At Mushroom and 

 Virgin Mound vent fluids were collected directly above the spires 

 and within the anhydrite chimney orifice, respectively. 



Because of calibration uncertainties (as shown previously) 

 the temperature data listed in Table 1 are given only for relative 

 comparison. The temperature maxima determined at these vents 

 during the 1987 Alvin dives are shown in Figure 1. 



DISCUSSION 



The Axial Volcano ASHES vent field data set presented here is 

 rather sparse with respect to the number of data points and their 

 spread along the seawater-hydrothermal fluid mixing line (the most 

 hydrothermally enriched sample contained only 33% pure vent fluid 

 based on the premise that the latter is characterized by a "0" Mg 

 value). Nevertheless, several preliminary observations are 

 offered while we await the results of determinations presently 

 underway on the 1987 vent fluid collection. 



The Axial data fall into two clearly distinct categories, 

 which are apparent from the plots of chloride, hydrogen sulfide, 

 manganese, and iron versus magnesium (Figs. 3 and 4). In each of 

 these plots we can distinguish two mixing lines: one between 

 seawater and a "normal" hydrothermal fluid endmember and another 

 between seawater and a low-salinity, metal-depleted, gas-enriched 

 fluid endmember. The elemental concentrations for the normal 

 hydrothermal fluid endmember at Axial Volcano fall within the 

 range of previously published data on ridgecrest hydrothermal 



39 



