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doi:10.2204/iodp.proc.314315316.209.2013

Introduction

Nankai Trough is one of the most extensively studied subduction zones in the world and is known as an area of active subsurface fluid circulation. The widely observed bottom-simulating reflectors suggest the presence of gas hydrates (Matsumoto et al., 2004). Many fractures and faults developed within the accretionary prism are most likely providing conduits of nutrient and energy substrates that potentially support indigenous microbial population and activities in the subsurface environment (Saito and Suzuki, 2007). Methane production derived from gas hydrate dissociation and migration of thermogenic gas from deeper depths are also expected. The carbon isotope compositions of methane in combination with gas molecular compositions have been widely used for the characterization of hydrocarbon gas origin (Bernard et al., 1977; Rice and Claypool, 1981). In this study, we measured the carbon isotope compositions of methane and molecular compositions in void gas samples from Site C0001, which will provide critical clues to the origin and migration paths of the hydrocarbon gas in this area.

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