Part III: Brittle, Ductile, and Viscous Deformation
Part III includes Chapter 4 (Brittle Deformation), Chapter 5 (Ductile Deformation) and Chapter 6 (Viscous Deformation). For each style of deformation we describe structures varying in scale from thin section to crustal, document laboratory experiments providing material property values, and review the constitutive equations and motion equations relevant to that style. For example, among many other applications:
- Chapter 4 illustrates the brittle deformation of limestone strata using the fractures and faults at Lilstock Beach, England;
- Chapter 5 investigates the ductile deformation of a bed of salt as it flows toward an ascending diapir in a sedimentary basin; and
- Chapter 6 describes the viscous deformation of magma flowing in the sills at Shonkin Sag, Montana.
Brittle deformation displayed as joints and faults
Outcrop of limestone bedding surface at Lilstock Beach, England, with opening fractures (joints). The step in the bedding surface next to the geologist’s boots marks a small shear fracture (fault), with the far side offset about 25 cm upward, relative to the near side. Scale is approximate in the foreground. See Engelder and Peacock, 2001, for detailed maps, outcrop photos, and structural interpretations of this area.
Ductile deformation during lateral flow of salt toward a diapir
Lateral flow of salt into a diapir with folding of layers near the boundaries. Sense of shearing reverses from floor to roof zone. Heterogeneity in material properties due to layering is not part of the ductile plastic model for this flow. Modified from Talbot and Jackson, 1987, Figure 12.
Viscous deformation during magma flow in sills
Photograph of Shonkin Sag laccolith (left) with sills (right) that intruded laterally into the horizontal sedimentary rock. The model for this flow considers a parallel-sided conduit and laminar viscous flow. See Pollard et al., 1975.