ABSTRACT

NW Pacific surface sediments are dominantly detrital with lesser amounts of biosiliceous and hydrogenous material. The detrital components change regularly from trench sediments dominated by island-arc volcanoclastic debris to open-ocean sediments with higher REE, Th, Rb, Cs, La/Yb_N, La/Sc and Th/Hf but lower Eu/Eu^*, Co/Th, K/Rb and Rb/Cs. The open-ocean sediments are dominated by upper continental crustal debris. Buried sediments from DSDP holes pass through a three-stage evolution: ocean-ridge basaltic debris and hydrothermal precipitates, abyssal plain sediments characterised by hydrogenous material and upper continental crustal debris, and near-shore island-arc detritus with intermittent air-fall ash. Biogenic and within-plate basaltic/hydrothermal components cause important local deviations from this evolution.