EarthRef.org Reference Database (ERR) -- Plank & Langmuir 1993

AT ocean trenches, sea-floor sediments may either be scraped off the subducting plate, or accompany it into the mantle. Some of the subducted sediment may then be recycled to the arc crust by magmatism1; the rest may be recycled into the mantle, and contribute to mantle heterogeneity2. Strong evidence for sediment contributions to are volcanism has come from isotope tracers, such as Pb-297 and Be-10 (refs 3-5), but a global mass balance requires consideration of element fluxes6. Here we report the sedimentary fluxes into eight trenches around the globe of trace elements that are enriched in are volcanics (Ba, Sr, K, Rb, Cs, La, Th and U)7. We show that the volcanic outputs clearly reflect the sediment inputs, once the effects of melting are taken into account8. Where the sediment flux into a trench is high for a particular element, the associated volcanics are enriched in this same element. Thus, some of the geochemical characteristics of arc volcanics can be traced back to the sediments at the trench. A mass balance of the inputs and outputs will ultimately provide estimates for how much sediment is recycled to the arc, and how much to the deeper mantle.