Subduction zones and their hydrocarbon systems

Subduction zones are common tectonic features central to large-scale crustal and elemental cycling, and they are accompanied by basins often with thick sedimentary fill and structures suitable for hydrocarbon preservation. However, significant hydrocarbon production occurs in only a handful of subduction zone locations. Here we explore our current understanding of the controls on hydrocarbon systems associated with subduction zones, in terms of the strongly variable conditions inherent to this tectonic setting that either favor or limit petroleum production, and in the context of three case studies (Cook Inlet and Sacramento basins, USA; Talara basin, Peru). This review concentrates on continental rather than intra-oceanic subduction settings due to limited basin preservation and hydrocarbon prospectivity in the latter. Overall, the primary limitations on hydrocarbon potential in forearc and/or trench-slope basins are time-to-maturation (low geothermal gradients), reservoir quality, source-rock presence and quality, structural complexity, and depth to reservoir. The latter two conditions may explain why offshore exploration has been limited near subduction zones, even where onshore production is robust and/or hydrocarbon seeps are common. Prospectivity may increase with enhanced seismic imaging and offshore infrastructure in some locations, and with the economic development of unconventional resources such as gas hydrates in accretionary prisms or deep shale gas in forearc basins. In any case, the presence of hydrocarbon systems in subduction zones, whether prospective or not, is an important part of the cycling of carbon and other elements at active convergent margins.