(Table 1) Bulk elemental composition at DSDP Holes 92-597, 92-598, and 92-599

The major element composition of Leg 92 sediments reflects the input of hydrothermal precipitates from the East Pacific Rise and extinct Mendoza Rise plus minor amounts of terrigenous detritus. The basal sediments are a mixture of hydrothermally precipitated ferromanganese oxyhydroxides and carbonates. In present and ancient sediments deposited 200 km or more from the rise crest, however, the amount of hydrothermal precipitates in the sediments decreases markedly. The distal deposits of hydrothermal particulates are also richer in iron because of fractionation by sedimentation processes. Slowly accumulating aluminosilicate detritus becomes a more important fraction of the sediments far from the rise crest as a result of the decrease of hydrothermal sedimentation.