Modeling Heat and Mass Transport in the TAG Active Hydrothermal Mound Using a Combined Theoretical/ Observational Approach

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Abstract P.I.: Tivey Proposal Number: 97-12153 Institution: WHOI Title: Modeling heat and mass transport in the TAG active hydrothermal mound using a combined theoretical/observational approach Ridge-crest hydrothermal systems play a fundamental role in transferring energy and mass fluxes from the Earth's interior to its surface. In the fall of 1994, 17 holes were drilled in the 200 meter diameter TAG active hydrothermal mound on the Mid-Atlantic Ridge during Leg 158 of the Ocean Drilling Program to investigate the fluid flow, geochemical fluxes, and the subsurface nature of an active hydrothermal mound. This mound is perhaps the closest mid-ocean ridge analog to Cyprus ore bodies and has an estimated convective heat flux from the black smokers of 225 MW, and from the entire mound area of 500-1000 MW. Theoretical calculations will be carried out to examine the relationships among the different fluids exiting the mound, and to examine the role of seawater entrainment at TAG, including the amount of seawater entrained, and what imprint such entrainment leaves in the deposits, and in fluids exiting the mound. Calculations of transport and reaction will also be done, allowing establishment of links between fluid chemistry and observed mineralogy and texture of drillcore samples. The emphasis will be on modeling processes occurring during the most recent phase of hydrothermal activity, i.e., related to (i) formation of anhydrite (CaSO4) veins, (ii) alteration and mineralization associated with veining, (iii) deposition of chimneys and sulfide crusts at the mound surface, and (iv) formation of fluids currently exiting the mound. These studies will allow quantification of mass fluxes and examination of processes involved in mineral deposition, zoning, and zone refinement in one of the largest known active hydrothermal mounds along the mid-ocean ridge sys tem.