Deformation and Intrusion in Deeply Buried Rocks: Creep, High-Angle Ductile and Brittle Shear, and Congruent Shear Arrays

Abstract

In a material, any stress produces a strain: small differential stresses result in flow, including creep; larger differential stresses produce shear fractures and brittle-ductile or ductile shear zones that form at low or high angles (less than or more than 45°) to the axis of greatest compressive stress (σ1). A new Continuum criterion for deformation allows us to graph the stresses that result in flow (including creep), and virtually any orientation of shear fracture or zone, whether brittle or ductile. In the Continuum criterion, the angle between shear fractures or zones and σ1 increases to values much greater than 45° with increasing confining pressure, or depth; flow is non-Newtonian because viscosity is stress dependant. Where shear fractures or shear zones form at angles other than 45° to the axis of greatest compressive stress, less work is done during deformation if the shear fractures or zones develop preferentially in en echelon arrays. In the absence of tension fractures, shear fractures act as conduits for magmatic and hydrothermal fluids; where the fractures comprise en echelon arrays, patterns of dyke or vein contacts reflect depth of emplacement.KeywordsShear ZoneShear BandShear FractureDuctile Shear ZoneMafic DykeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.