Detailed studies of the major element geochemistry, oxygen and hydrogen isotope ratios of pore fluids, and the 87Sr/86Sr ratio of dissolved strontium have made it possible to unravel physical and chemical processes that affect the pore fluid chemistry in a transect of drill holes across the northern Barbados accretionary complex. These processes include (1) alteration of volcanic ash buried in the Pleistocene-Pliocene sediment column; (2) alteration of underlying basalts of layer 2 of the oceanic crust; (3) movement of fluids from deep in the accretionary complex along fault zones (particularly the d¿collement) annd minor permeable layers; these fluids from deeper in the complex are characterized by low chloride concentrations and increased Δ18O(H2O) values, presumably as a result of dehydration of smectite interlayers; and (4) mixing processes involving the migrating fluids cause incongruities in the geochemical anomalies of these fluids. ¿ American Geophysical Union 1990