EarthRef.org Reference Database (ERR) -- Lin 1992

Rare earth element (REE) and Ned isotopic data for ten representative samples of Lower Cretaceous to Miocene pelagic sediments from the western Pacific indicate a wide range of compositions for sediments being subducted beneath the Mariana and Volcano arcs. All samples are enriched in light rare earth elements (LREEs) and show negative Eu and Ce anomalies. The values of epsilon(Nd) range from + 0.6 to -7.3. These data are used to calculate the Bulk Western Pacific Sediment (BWPS), which is characterized by low Sr/Nd (10), Ba/La (13), and epsilon(Nd) (-5.2) and high Sr-87/Sr-86 (0.7078) compared to that of Mariana and Volcano arc lavas. This composite sediment is used to refine a mixing model for the origin of Mariana and Volcano arc melts. Some lavas from the northern Mariana Arc have Ba/La higher than that of BWPS, which indicates that a third component is required. The high Ba/La in the mantle source for these lavas is interpreted to result from multiple episodes of fluid fractionation. The mixing model indicates that a minor amount of sediment and a low proportion of metasomatic fluid fluxes the mantle source at a late stage when the subarc mantle is already highly metasomatized. This model also suggests that the mantle source for arc melts is affected more by metasomatic fluids than by melting or bulk mixing of sediments.