A two-dimensional model of the methane cycle in a sedimentary accretionary wedge

[摘要] A two-dimensional model of sediment column geophysics and geochemistry hasbeen adapted to the problem of an accretionary wedge formation, patternedafter the margin of the Juan de Fuca plate as it subducts under the NorthAmerican plate. Much of the model description is given in a companion paperabout the application of the model to an idealized passive margin setting;here we build on that formulation to simulate the impact of the sedimentdeformation, as it approaches the subduction zone, on the methane cycle. Theactive margin configuration of the model shares sensitivities with thepassive margin configuration, in that sensitivities to organic carbondeposition and respiration kinetics, and to vertical bubble transport andredissolution in the sediment, are stronger than the sensitivity to oceantemperature. The active margin simulation shows a complex sensitivity ofhydrate inventory to plate subduction velocity, with results dependingstrongly on the geothermal heat flux. In low heat-flux conditions, the modelproduces a larger inventory of hydrate per meter of coastline in the passivemargin than active margin configurations. However, the local hydrateconcentrations, as pore volume saturation, are higher in the active settingthan in the passive, as generally observed in the field.

[学科分类] 地球化学与岩石