THE MICROSTRUCTURAL EVOLUTION OF FLUID-FLOW PATHS IN SEMI-LITHIFIED SEDIMENTS FROM SUBDUCTION COMPLEXES

The characterization of the fluid migration pathways is essential to an understanding of the hydrodynamics of accretionary wedges located in the high levels of subduction zones. Microstructural analysis of the fluid flow pathways can provide constraints on (a) the porosity/permeability evolution of different migration pathways, (b) the deformation mechanisms histories which promote different fluid flow characteristics, (c) the interconnectivity of migration pathways. Three important fluid migration pathways can be recognized in accretionary wedges; bulk flow through the sediment, localized flow through fracture networks and localized flow along fault zones. The recent progress made towards understanding the microfabric evolution in each of these pathways in semi-lithified sediments is reviewed. The analysis highlights the role of transient deformation events in these materials and the need to characterize the detailed deformation mechanism paths and syn-deformational (dynamic) properties associated with these events.