Abstract

A steeply dipping shear zone is present in augen schists and green phyllites of the Ordovician Tetagouche Group, a multiply deformed volcanic-sedimentary complex in the Canadian Appalachians. The shear zone developed early in the tectonic history, and constituent rocks are marked by foliation transposition, strong extension, and mylonitic (or phyllonitic) microstructures.

Dynamic recrystallization was an important deformation process, but the L/S tectonites also contain various generations of veins. The deformation of these veins, in combination with relict crack-seal vein microstructures, vein-controlled alteration, and the differentiation of the tectonic layering, illustrates pervasive solution transfer during shear-zone evolution.

Various stages of brittle/ductile deformation can be recognized in veins of different ages. This reflects a microstructural competition between solute mass transfer and crystal-plastic processes, which is discussed in terms of "wet" versus "dry" mylonitization.

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