Shape fabrics and superimposed simple shear strain in a Precambrian shear belt, W Greenland

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Abstract
Shape fabric type in the northern part of the Ikertôq shear belt and the adjacent area has been recorded both qualitatively and quantitatively, and its variation is described. Shape fabric variation is shown to be closely related to structural changes, and both are reconciled with a deformation model involving superimposed strain. In the shear belt itself finite strain shape fabrics are shown to be a consequence of superimposition of 2 differently orientated simple shear strains. The earlier simple shear strain initiated the shear belt and was characterized by horizontal ENE-WSW movements in a vertical shear plane. The second deformation was produced by overthrusting in a SSE direction. In effect the XZ plane of the later deformation was superimposed on YZ sections through shape fabrics produced by transcurrent movements. The overthrusting deformation was superimposed on earlier structures with gradually increasing intensity, allowing the resultant deformation path to be recorded in detail. A steep strain gradient marks the northern boundary of the shear belt, but low deformation of shear belt age can still be recognized further N. Shape fabric variation N of this limit of intense strain is described. Structural and shape fabric variation in this area is a consequence of superimposition of low magnitudes of overthrusting simple shear strain on pre-shear belt structures and fabrics.