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ABSTRACT

Microprobe analysis of plagioclase in deep-sea sands from various tectonic settings gives averages ranging from 19% An for trailing-edge continental margins to 56% An for basins on the ocean side of an island arc. For each setting except island arcs, anomalously high amounts of pure albite are found. These albitic grains may be recycled from pre-existing sedimentary rocks. Potassium-rich plagioclase, thought to be indicative of a volcanic provenance, is less abundant than would be expected from the proportion of volcanic rock fragments. Perhaps such high-K plagioclases are less resistant to weathering than low-K plagioclase.