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

Fehn（0550122）知识价值：天然气水合物和泥火山与天然气主要成分甲烷的形成和释放有关。这两种现象（天然气水合物由困在水冰中的甲烷组成，泥火山是富含甲烷流体的管道）在大陆边缘非常常见，构成了一个巨大的甲烷储层。虽然现在人们普遍认为，天然气水合物中甲烷的含碳量与所有传统化石燃料储层的含碳量一样多，甚至更多，但这些甲烷的来源还没有得到很好的了解。这项研究利用从天然气水合物和泥火山收集的含甲烷流体中的宇宙成因碘（碘129）来测定大陆边缘甲烷来源的年龄。本研究旨在确定两个对比环境中的甲烷来源地层：日本的南开海槽和哥斯达黎加的大陆边缘。样品已经到手，日本和德国的合作者已经对大量互补的地球化学物种进行了分析。样品的卤素浓度将使用ICP-MS和离子色谱分析。宇宙成因碘比值将使用普度大学PrimeLab的加速器质谱系统进行测量。测定的年龄将与三个潜在的有机物质来源的年龄进行比较，以检验：(1)甲烷的形成是一个局部事件，主要是由当前形成的沉积物中有机物质的存在所主导；(2)甲烷与活动边缘海洋沉积物的俯冲有关；或者(3)甲烷是由于上覆板块中存在古老的有机物质。一旦确定了源地层，就可以估计源与当前位置之间的距离，并将其与活动边缘的流体流动模型联系起来。更广泛的影响：这项研究支持研究生和本科生的培训，以及纽约州一所大学教员的研究。一名日本博士后也将参与该项目，并在首席研究员的美国实验室工作，该项目无需支付任何费用。该项目是美国、日本和德国机构之间的国际合作，包括参与大学之间的学生和教师交流。

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.