Strain shadow

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[Geometry-mechanism]-----Cone-shaped domain adjacent to a porphyroclastor porphyroblast in the direction of the foliationand usually composed of another mineral than the porphyroclastor -blast. It forms by rearrangement of materialin response to inhomogeneous deformation of thematrix adjacent to the porphyroclast or -blast. Strainshadows are usually massive or contain equidimensionalcrystals; if they contain fibres, the term strain fringe isused instead. A mantled porphyroclast differs from a strainshadow in that the mantle has the same mineral compositionas the porphyroclast and is inferred to have formedat the expense of the porphyroclast by recrystallisation. (Passchier and Trouw, 2005, Microtectonics)