The Fine-Scale Hydrogeology & Geochemistry of the Areeas of Active Venting in Middle Valley, a Sedimented Rift of the Northern Juan De Fuca Ridge

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Baker 9417011 This research program, involving researchers from Indiana, Duke and Columbia Universities, proposes to investigate in detail the processes involved in circulation of hydrothermal fluids in a heavily sedimented setting adjacent to active hot springs on Juan de Fuca Ridge, a mid-ocean ridge spreading center located off Oregon, Washington and western Canada. The specific programs proposed for the one-month field effort include studies of heat, chemical and fluid transport within the sedimentary section and the physical properties of those sediments. The objective in acquiring this detailed, multicomponent data set is to use these three interdependent components to constrain and define models of the fluid pathways and chemical reactions, including the deposition of sulfide minerals within the mud and rock overlying the thermal vents. The detailed program is possible in part because it uses cutting edge technology for heat flow and pore water measurement, which this group of investigators has been instrumental in fostering and bringing to use. Previous study at the two proposed sites includes drilling by the NSF-sponsored Ocean Drilling Program vessel JOIDES Resolution, and the new data allows extrapolation of results both areally (with new measurements from the upper 20 meters of the sediments) and with depth (with existing drilling data and planned future drill data, which is expected in the 1996- 97 time frame) to define the 3-dimensional architecture of circulation and mineralization. In addition to providing the first study at this level of detail over sedimented hot springs known to produce large mineralized deposits, the program will provide valuable data for precise selection of sites for future drilling.