LITHIUM, BORON, AND THEIR ISOTOPES IN SEDIMENTS AND PORE WATERS OF OCEAN DRILLING PROGRAM SITE-808, NANKAI TROUGH - IMPLICATIONS FOR FLUID EXPULSION IN ACCRETIONARY PRISMS

Results from a comprehensive study of B, delta(11)B, Li, and delta(6)L i distributions in both sediment and pore-water samples of Ocean Drill ing Program Site 808, Nankai Trough, Japan, show a strong correlation between Li and B concentrations, in agreement with previously publishe d information from surface-marine sediments, suggesting similar geoche mical behavior in sedimentary environments. The delta(6)Li and delta(1 1)B analyses provide additional data on the systematics of Li and B in marine sediments. Our results provide information on fluid-expulsion activity that has occurred at this drill site. Anomalies in all these constituents in the vicinity of the decollement zone (similar to 960 m below sea floor [m bsf]) suggest an influx of deeply generated fluids having distinct chemical compositions. The maximum concentrations of B and Li in bulk sediment, as well as their corresponding isotopic com positions, suggest uptake of both elements via chemisorption or second ary-mineral formation near the fluid conduit associated with the decol lement zone. The low delta(11)B in pore waters suggests contribution o f exchangeable plus lattice-bound B from greater depths. The correspon ding high delta(6)Li similarly indicates mobilization from sediment un der high-temperature conditions.