Chemical composition of Pacific sediments near 20°S

Six GEOMETEP cores sampled along a transect about 100 km long centered on the East Pacific Rise are compared with six DSDP Leg 92 cores sampled along a transect 350 to 1250 km west of the crest of East Pacific Rise. The influence of hydrothermal precipitation on the chemical character of the samples from both transects is strong and decreases with distance from the East Pacific Rise. Both the amount and the chemical composition of the hydrothermal precipitates change with distance. Near the rise, the precipitates are enriched in manganese and silica; with increasing distance from the rise the precipitates contain higher proportions of iron. The boron enrichment in the hydrothermal precipitates may outweigh the boron enrichment in marine clay minerals.
Hydrothermal production of barite and apatite at the East Pacific Rise is somewhat masked by contributions from the dissolution of calcareous tests. Hydrothermal and residual apatite can be distinguished by their yttrium contents.