Abstract
ABSTRACTRare earth element (REE) distributions and 87Sr/86Sr ratios were determined for nodule crusts and associated surface sediments collected in the southeastern Pacific Ocean between South America and the Tuamotu archipelago. The shale‐normalized patterns of the REE from the surface sediments show pronounced negative anomalies in Ce which indicate a marine origin. One 87Sr/86Sr ratio also has a value characteristic for seawater strontium. REE patterns from the nodule crusts, when normalized to shales, seawater or associated surface sediment, show that a marine origin can also be proposed for the oxy‐hydroxides. Only the Ce shows a systematic scatter, which could be the result of fluctuations in the oxidation‐reduction conditions during nodule growth. The marine origin for REE is corroborated by the 87Sr/86Sr ratios which average 0 · 70905 ± 0 · 00019 (2σ), a value close to the seawater 87Sr/86Sr ratio of 0·70910 ± 0 · 00035. If the major metals of the polymetallic nodules have the same origin as these trace elements, then a direct precipitation from seawater can be postulated for the crusts studied here.
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