Source and migration of iodine in pore waters across the Nankai Trough: Distribution of long-lived radio isotope of iodine (I-129) along the NanTroSEIZE transect
Abstract
Iodine concentrations and 129I/I ratios were determined in pore waters from the Nankai Trough subduction system, covering inputting oceanic sediment to accretionary prism collected during the Integrated Ocean Drilling Program Expeditions 315, 316, 322, and 333. While the vertical patterns of iodine concentration correlate well with organic matter content in the potential iodine source formations, the 129I/I ratios significantly point to the difference of source materials for iodine principally constrained by the location in the accretionary system. The 129I/I ratios result in ages for the organic-rich iodine source formation between 30 and 45 Ma in the accretionary prism, suggesting that iodine older than their host sediments dominates in the entire sediment body. Significant increases of 129I/I ratio (decrease in age) are found just above the lithologic boundary between the forearc basin and accreted sediments, and near the megasplay fault zone branching from the interface of the subducted hemipelagic sediments and the overlying accreted sediments. The former represents limited migration of ascending deep fluids beyond the lithologic boundary where sediment porosity drops discontinuously, causing fluids to move preferentially along the lithologic boundary. The latter is a result of fluid migration from the root of the megasplay fault on the Philippine Sea Plate, where relatively young iodine delivered from the subducted sediments is responsible for the observed high 129I/I ratios near the shallow region of the megasplay fault. On the other hand, the minimum iodine ages on the toe of the accretionary wedge are younger than those in the accretionary body, indicating different source and migration processes in the frontal thrust system. Iodine form thin-young inputting hemipelagic sediments are significantly younger than any other sites, <10 Ma, mixing at the frontal thrust zone causes potential decreases in iodine ages. The results here indicate that 129I/I dating of pore water can be used to describe the source and mode of fluid migration constrained by accretionary processes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.T31F2575T
- Keywords:
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- 1031 GEOCHEMISTRY Subduction zone processes;
- 1040 GEOCHEMISTRY Radiogenic isotope geochemistry;
- 1050 GEOCHEMISTRY Marine geochemistry