Fluid Flow and Dehydration Reactions Inferred from Chloride Anomalies at Three Accretionary Complexes

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Continental margin accretionary complexes are sites of large- scale fluid transport of dissolved matter. Deformation and compaction processes occuring in accretionary terranes are resposible for increasing pore pressures producing these large scale fluid-flows. Temperature and pressure conditions in these areas are beleived to be responsible for the dehydration of hydrous minerals which then result in the formation of low chloride fluids. Variations in chloride concentrations are an essential part of the observations used to infer preferential pathways and transient flow episodes in accretionary prisms. These poorly understood material-transport processes exert a first-order control on the geochemical and thermal balance of the earth's reservoirs. This award will support Dr. Dreiss' efforts to investigate the origin of low chlorinity fluids and to develop a combination of fluid and mass transport models in three acccretionary complexes (Barbados, Nankai, and the Peru margin). Dr. Dreiss proposes to develop models which can can be used to test the hypothesized sources of low-chloride fluids and transport mechanisms with known information about site geometry, sediment permeabilities, and pore water compositions. These models will provide indepen- dent estimates of fluid flow which can be compared to those derived from heat transport studies.