Effect of Conductive Cooling on Chemistry of Midocean Ridge Hydrothermal Fluids: Experimental and Theoretical Constraints

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Hot spring fluids issuing from the vents have been sampled at numerous sites on actively spreading mid-ocean ridges. The chemistry of these fluids has been extensively studied to provide insights on the processes occurring at depth in the ocean crust, and to constrain the hydrothermal flux of elements into and out of seawater. Although measured temperatures of vent fluids are generally around 350~ or less, these fluids have experienced much higher temperatures as evidenced by a number of chemical geothermometers . The discrepancy between measured temperatures and temperatures inferred from the dissolved concentrations of temperature dependent species can be largely attributed to conductive cooling of high temperature fluids in up-flow zones. However, before one can use the chemistry of hot spring fluids to access unambiguously condi t ions and processes in subseafloor reaction zone, it is important to understand the role of heat loss on vent fluid chemistry. Based on recent results of mineral solubility experiments designed to determine and retrieve thermodynamic data for H2, H2S, and Fe-, and Cu-bearing species, we can now constrain the effect of heat loss by conduction on the chemistry of hot spring fluids.