GEOLOGY 1 Lecture Notes - Lecture 17: Calcite, Rigid Body, Mylonite
Document Summary
Systematic variations in orientations across shear zone. Reflects s1s2 (xy) plane of finite strain ellipsoid (simple shear) Subparallel to shear zone boundaries in centre of shear zone where shear is highest. Most shear zones have one foliation at angle < 45 degrees to boundary. Crystal- plastic processes elongate crystals to extension. Third foliation may occur oriented oblique to boundary. Foliation is called c" foliation and crenulates mylonitic foliation. S points in shear direction, displacement on c" is same as shear zone. Form on flanks of rigid inclusions in shear zones. Rigid inclusion shields matrix on flanks from strain. Most are microscopic, seen in thin section. Grains in matrix may have tails that form during deformation. Grains are rigid bodies that rotate during deformation. Initially form at 45 degrees to shear zone. Subsequently rotate to steeper angle while new part of vein forms at 45 degrees. Permanent, nonrecoverable change due to growth of fractures and/or sliding on pre-existing fractures.
