The relationship between Precambrian shear belts and modern fault systems

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Abstract
Deformation in the brittle (seismic) mode is characteristic of the upper parts of fault systems, while at lower levels displacements are predominántly ductile (aseismic). It is suggested that the geometry and products of ductile and brittle displacements can be examined in eroded Precambrian faults. The Ikertôq shear belt in western Greenland is cited as an example of how, due to uplift and erosion, all the deformation products which occur through the vertical extent of fault systems, and the geometry of deformation processes associated with the formation of these products, can be observed at the present erosion level in a Precambrian shear belt. It is argued that this circumstance allows the use of Precambrian faults to infer the various deformation processes occurring in modern, highly active, fault systems.