The interplay of permeability and fluid properties as a first order control of heat transport, venting temperatures and order control of heat transport, venting temperatures andventing salinities at mid-ocean ridge hydrothermal systems

摘要

While the fundamental influence of fluid properties on venting temperatures in mid-ocean ridge (MOR) hydro-nthermal systems is now well established, the potential interplay of fluid properties with permeability in controllingnheat transfer, venting temperatures, and venting salinities has so far received little attention. A series of numericalnsimulations of fully transient fluid flow in a generic, across-axis model of a MOR with a heat input equivalent tonmagmatic supply at a spreading rate of 10 cm yearn)1nshows a strong dependence of venting temperature andnsalinity on the system’s permeability. At high permeability, venting temperatures are low because fluid fluxes arenso high that the basal conductive heating cannot warm the large fluid masses rapidly enough. The highest vent-ning temperature around 400u0002C as well as sub-seafloor fluid phase separation occur when the permeability is justnhigh enough that the fluid flux can still accommodate all heat input for advection, or for lower permeabilitiesnwhere advection is no longer capable to transfer all incoming magmatic heat. In the latter case, additional mecha-nnisms such as eruptions of basaltic magma may become relevant in balancing heat flow in MOR settings. Thenresults can quantitatively be explained by the ‘fluxibility’ hypothesis of Jupp & Schultz (Nature, 403, 2000, 880),nwhich is used to derive diagrams for the relations between basal heat input, permeability and venting tempera-ntures. Its predictive capabilities are tested against additional simulations. Potential implications of this work arenthat permeability in high-temperature MOR hydrothermal systems may be lower than previously thought andnthat low-temperature systems at high permeability may be an efficient way of removing heat at MOR.