MOBILIZATION OF BERYLLIUM IN THE SEDIMENTARY COLUMN AT CONVERGENT MARGINS

Studies of Be distributions in subduction zone sediments will help to understand questions regarding the enrichments of cosmogenic Be-10 in arc volcanic rocks. Analyses of Be-10 and Be-9 in sediments of Ocean D rilling Program Site 808, Nankai Trough and Be-9 in porewaters of Site 808 and Sites 671 and 672, Barbados ridge complex, show significant d ecreases in solid phase Be-10 and large increases of porewater Be-9 at the location of the decollement zone and below or at potential flow c onduits. These data imply the potential mobilization of Be during pore fluid expulsion upon sediment burial. Experiments involving reaction between a decollement sediment and a synthetic NaCl-CaCl2 solution at elevated pressure and temperatures were conducted in an attempt to mim ic early subduction zone processes. The results demonstrate that Be is mobilized under elevated pressure and temperature with a strong pH de pendence. The Be mobilization provides an explanation of Be-10 enrichm ent in arc volcanic rocks and supports the argument of the importance of the fluid processes in subduction zones at convergent margins.