OCE 98-11557 Kastner OCE 98-12121 Wheat The recommended Collaborative project involves retrieval in 1999 of four OsmoSamplers deployed by the JOIDES Resolution in holes drilled in 1996 on the eastern flank of the Juan de Fuca Ridge during ODP Leg 168. In addition, liter-volume samples will be collected at the base of the boreholes, and borehole fluid temperature measurements will also be made. These holes were sealed with the ODP CORKs, which allow instrument retrieval and data readout through ports and interfaces to instrument strings on their top surface. Retrieval involves five days of use of the Alvin submersible in association with a Wireline Re-entry Tool (WRT), further development of which will be funded by this proposal. After retrieval, the OsmoSampler samples, representing a continuous record of borehole fluid composition for three years, will be analyzed for a large range of major, minor and trace elements, including Na, K, Li, Rb, Sr, Si, B, Ba, Mn, Fe, Br, F, NH4, NO3, PO4, SO4, and the rare earth elements. They will also be analyzed for a wide range of isotopic compositions, including those of H, O, Sr, B, Li, Cl, and Be. The large volume samples will be analyzed for tritium (to check for borehole fluid contamination with ambient seawater), Ar, Xe, CO2, and CH4 concentrations, for He isotopic composition, and for C isotopes if enough CO2 and CH4 are present. The holes in the CORK will be capped after retrieval, with emplacement of a new instrument "cap" at one hole (Site 1026) for evaluation of the chemical response to local hydrographic changes where over-pressured basement fluids are currently venting. This project will represent the best opportunity to date to obtain actual formation fluids that are circulating within the oceanic crust. These samples will allow a fundamental examination of alteration processes occurring within the crystalline oceanic crust as it ages, providing a means for testing models of chemical flux between oceanic basement and seawater essential t owards understanding the composition of both. ***
