Geochemistry, Geophysics, Geosystems

Dynamics of outer-rise faulting in oceanic-continental subduction systems

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Abstract

[1] During subduction, bending of downgoing oceanic lithosphere gives rise to normal faulting due to the extensional stress state generated in the upper plate. As deformation patterns inherently reflect a material's state of stress and rheology, extensive global observations of outer-rise faulting patterns and subduction dynamics provide a unique opportunity to examine the factors controlling outer-rise deformation. Despite a wide range of observed oceanic plate ages, convergence rates and slab pull magnitudes across modern subduction systems, however, measured outer-rise faulting patterns show effectively no correlation to variations in these parameters. This lack of correlation may reflect that outer-rise faulting patterns are strongly sensitive to all of these parameters, are dependent on additional parameters such as downgoing-overriding plate coupling or that existing faulting measurements require additional analysis. In order to provide a basis for future analysis of outer-rise faulting patterns, we build on previous thermo-mechanical numerical models of outer-rise deformation and explore the relationship between outer-rise faulting patterns, subduction dynamics and brittle rheology in an oceanic-continental subduction system. Analysis of time-averaged outer-rise faulting patterns indicates that downgoing plate age and velocity, downgoing-overriding plate coupling and slab pull all significantly affect faulting patterns, while variations in brittle rheology have a significantly smaller impact. These relationships reflect that the sensitivity of outer-rise faulting patterns to the frictional properties of the oceanic crust and mantle is small compared to variations in the overall stress state and deformation rate of subduction systems. In order to gain additional insight into the origin outer-rise faulting patterns, future numerical studies should focus on specific regions in order to place constraints on the structure of the downgoing plate and dynamics of the subduction system.

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