Age discrepancy of pore water iodine-129 between forearc and accreted sediments from NanTroSEIZE Sites C0001 and C0002, Nankai Trough, Japan
Abstract
Integrated Ocean Drilling Program (IODP) Expedition 315, part of the multistage Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), provided an excellent opportunity to compare the fluid regime in the old accreted and overlying young forearc sediments. We cored the Kumano forearc basin sediment downhole to the upper accretionary prism in the Nankai Trough, Japan, with the D/V Chikyu in 2007. The I-129 system, a recently developed cosmogenic isotopic system, has been applied to pore waters collected from two deep cores in order to determine sources for fluids in different parts across the trough. The iodine ages in pore waters collected from the landward site (C0002) are close to 30 Ma throughout the sediment column, suggesting uniform fluid system between the lithologic units. Similar ages are found only in the accretionary prism at the seaward site (C0001), those in the overlying basin sediment are, however, significantly younger, suggesting a limited migration of upwelling deep fluids beyond the lithologic boundary where porosity considerably drops. The results suggest that deep, old sources are responsible for most of the iodine in these cores, but that differences in hydrologic behavior, related to changes in porosity in the basin sediments, prevent deep fluids to migrate to the surface at the seaward site.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T31B1993T
- Keywords:
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- 1115 Radioisotope geochronology;
- 3036 Ocean drilling