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Dissolution of quartz and the recrystallization and re-equilibration of phyllosilicates produce the dark anastomosing seams that dominate microstructures of tectonic mClange which occur in a low-grade, imbricated and multiply deformed, mid-Palaeozoic, intracratonic flysch sequence in northeastern Australia. Seams are composed of very closely spaced or coalesced cleavage lamellae, which are very thin layers of extremely fine-grained phyllosilicates. Cleavage seams enclose lenses of siltstone or greywacke, which formerly occurred in continuous sedimentary layers, indicating extremely heterogeneous and disruptive deformation. Microphacoids enclosed by cleavage seams have subtle shape asymmetries analogous to those of porphyroclasts. Phyllosilicatepreferred orientations within microphacoids commonly lie at a low angle to enclosing seams, and asymmetric relationships occur within seams, The shape and fabric asymmetries appear to be constant, and are regarded as analgous to S and C planes. The number and extent of seams, the amount of dissolution they indicate, and the efficiency of deformation partitioning imply some enhancement of chemical activity and substantial silica loss from the system. This, in turn, suggests the passage of large amount of silica-undersaturated fluid, and mClanges may be zones of high fluid flow. However, the microstructures and the disruptive nature of the fabrics may also reflect the influence of high bulk shear strains and suggest some relationship between the shearing component of deformation and the development of cleavages and foliations.

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