Geochemistry at DSDP Leg 58 Holes

Chemical features indicate that the Shikoku Basin sediments are typically terrigenous and were derived mostly from the Japanese Islands. A local contribution from oceanic islands, such as the Izu-Mariana Islands, to the basin sediments is not as large as expected from geophysical evidence.

The Nankai Trough cannot be a barrier against sediment influx to the basin from the Japanese Islands. Except for Ca and Mn, the bulk chemical composition of the sediments is inherited from the source materials, such as granites and volcanics in the Japanese Islands, without remarkable modification. Basal sediments immediately on the basaltic basement, enriched in Mn and Fe, formed under the effect of hydrothermal emanations related to volcanism.