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Bulk chemical composition of 279 samples of argillaceous sedi-ments from DSDP Sites 442, 443, and 444 in the Shikoku Basin (Leg 58) was determined and interpreted. Chemical features indicate that the Shikoku Basin sediments are typically terrigenous and were de-rived mostly from the Japanese Islands. A local contribution from oceanic islands, such as the Izu-Mariana Islands, to the basin sedi-ments 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 ef-fect of hydrothermal emanations related to volcanism. From the chemical composition of the sediments, using the formula of Boström et al. (1976), the spreading rate of the Shikoku Basin at 17 to 15 Ma is estimated to have been 1.7 cm/yr, which is not inconsis-tent with the rate determined from geophysical data

Year: 2014
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