I-129 and halogen systematics in pore waters from gas hydrates and mud volcanoes: Nankai Trough and Costa Rica Margin

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ABSTRACT Fehn (0550122) Intellectual Merit: Gas hydrates and mud volcanoes are related to the formation and release of methane, the main ingredient of natural gas. Both occurrences (gas hydrates consist of methane trapped in water ice, and mud volcanoes are conduits of methane rich fluids) are very common along continental margins and constitute a large reservoir of methane. While it is now well accepted that the amount of methane trapped in gas hydrates contains as much or more carbon than all the reservoirs of conventional fossil fuel combined, the origin of this methane is not well understood. This research uses cosmogenically produced iodine (iodine 129) in methane-bearing fluids collected from gas hydrates and mud volcanoes to age date the sources of methane in continental margins. This research seeks to identify source formations for methane in two contrasting environments: the Nankai Trough off Japan and the continental margin off Costa Rica. Samples are already in hand and have been analyzed for a large number of complementary geochemical species by collaborators in Japan and Germany. Halogen concentrations of the samples will be analyzed using ICP-MS and ion chromatography. Cosmogenic iodine ratios will be measured using accelerator mass spectrometry system of PrimeLab, Purdue U. The determined ages will be compared to those of the three potential sources of organic material to examine if: (1), the formation of methane is a local event, dominated by the presence of organic material in currently forming sediments, (2) methane is related to the subduction of marine sediments in active margins; or (3) methane is due to the presence of old organic material in the overriding plate. Once the source formations have been determined, distance between source and current location will be estimated and related to models of fluid flow in active margins. Broader Impacts: This research supports graduate and undergraduate student training, as well as the research of a faculty member at a university in New York State. A Japanese postdoc will also participate in the project and work in the US lab of the principal investigator at no cost to the program. The project is an international collaboration between US, Japanese, and German institutions and includes exchanges of students and faculty between the participating universities.