HIRONO, TETSURO, and SATORU NAKASHIMA
Dept. of Earth & Planetary Sciences, Hokkaido Univ., Japan

Abstract: Heterogeneous Pore Structures and Fluid Flow Properties in Deformed Sedimentary Rocks from the Shimanto Accretionary Complex

Subduction zones can be likened to a gigantic press where low density geological materials saturated with seawater are progressively squeezed between the overriding and under-riding lithospheric plates and the fluids expelled. Fluid expulsion is an important feature of accretionary prisms formed in the upper parts of subduction zones. The nature of fluid pathways is complex and depends upon permeability, porosity and hydraulic gradient. Permeability and porosity are the main control on fluid flow within accretionary prisms, yet they are ones of the most difficult parameters to accurately determine.

The pores of fractures and shear zones form interconnected networks through which fluid flows. It is suggested that the property of fluid flow in the porous deformed media is strongly affected by the pore structure. In order to characterize the detailed pore structures of deformed sedimentary rocks from an accretionary complex (Shimanto, Japan), the following techniques have been employed: (1) visual image analysis under an optical microscope of the pore space filled with colored epoxy resin, (2) nondestructive imaging technique using X-ray computerized tomography and (3) measurements of the roughness of grain and pore structures by atomic force microscope (AFIVI). The heterogeneity of pore structures was quantitatively determined, and its relation to transport properties, permeability, are discussed. Basic characterization of hydrodynamic transition of accretionary wedges is discussed too.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California