Hydrothermal vent fluids, chemistry fluid composition

The compositions of vent fluids found on the global MOR system are of interest for several reasons how and why those compositions vary has important implications. The overarching question, as mentioned in Section 6.07.1.3, is to determine how the fluids emitted from these systems influence and control ocean chemistry, on both short and long timescales. This question is very difhcult to address in a quantitative manner because, in addition to all the heat flux and related water flux uncertainties discussed in Section 6.07.1, it also requires an understanding of the range of chemical variation in these systems and an understanding of the mechanisms and variables that control vent-fluid chemistries and temperatures. Essentially every hydrothermal vent that is discovered has a different composition (e.g.. Von Damm, 1995) and we now know that these compositions often vary profoundly on short... 

The influence of these processes on the composition of Mesoarchean seawater is still unclear. De Ronde et al. (1997) have studied the fluid chemistry of what they believe are Archean seafloor hydrothermal vents, and have explored the implications of their analyses for the composition of contemporary seawater. They estimate that seawater contained 920 mmol Cl, 2.25 mmol Br, 2.3 mmol L i SO4, 0.037 mmolL I, 789 mmol Na, 5.1 mmol NH4, 18.9 mmol K, 50.9 mmol L Mg, 232 mmol Ca, and 4.52 mmol Sr. This composition, if correct, implies that Archean seawater was rather similar to modern seawater. 

De Ronde C. E. J., Channer R. M., Faure de R., Bray C. J., and Spooner E. T. C. (1997) Fluid chemistry of Archean seafloor hydrothermal vents implications for the composition of circa 3.2 Ga seawater. Geochim. Cosmochim. Acta 61, 4025-4042. 

The above argument on the calculation of chemical composition of ore fluids, seawater-rock interaction experiments, and isotopic compositions of ore fluids clearly demonstrates that Kuroko ore fluids were generated by seawater-rock interaction at elevated temperatures. The chemistry of present-day hydrothermal solution venting from back-arc basins and midoceanic ridges (sections 2.3 and 2.4) also support this view. 

---