ABSTRACT
In contrast, the higher pressures associated with ductile faults tends to inhibit open fractures unless fluid is available, at or near lithostatic pressure, to support them. Because they generally lack open fractures, ductile faults do not commonly have the hydrothermal alteration that is characteristic of many brittle fault zones. Despite that, ductile fault zones commonly have chemical compositions, mineralogy, or mineral proportions that differ from less deformed surrounding rocks. This difference may result from movement (addition and/or removal) of chemical components by flowing fluid. Alternatively, the ductile fault zone may have developed where it did because those rocks were originally different, and weaker, in the first place.
