6533b7d9fe1ef96bd126bfd2

RESEARCH PRODUCT

Conflicting shear sense indicators in shear zones; the problem of non-ideal sections

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Abstract Deflection of pre-existing planar structures such as foliations or veins by ductile shear zones is geometrically very similar to the curvature of newly developed shear zone-restricted foliations in zones that cut a rock with a random fabric. Sense of curvature of shear zone-restricted foliations can be used to determine shear sense, but the deflection of pre-existing planar structures is less reliable. Two examples are presented of shear zones in Australia where both types of structures seem to represent conflicting shear sense. This conflict can be attributed to a geometrical effect which causes deflection of older structures in an opposite direction to shear sense on outcrop surfaces oblique to the displacement vector. If the orientation of the displacement vector cannot be accurately determined in shear zones, e.g. because of limited outcrop or unclear lineations, most shear sense indicators can still be used to determine shear sense, but pre-existing planar structures are notoriously unreliable.