Deformation and Mountain Building

Strike and Dip-The Orientation of Deformed Rock Layers

Strike and Dip-The Orientation of Deformed Rock Layers

 Strike and dip are measurements used to describe a rock body's orientation with respect to the horizontal.

 Strike is the intersection of a horizontal plane with an inclined plane.

 Dip direction is the direction of inclination of the plane.

 Dip angle is the maximum angle of an inclined plane.

Fig. 10.5b p. 249

Rock Deformation - How Does it Occur?

 Applied stresses can deform or strain rocks until they become contorted or fracture.

 Stresses are categorized as compressional, tensional or shear.

 Stress is a force  Strain is the change in

shape that results from the stress being applied.

 Deformation and strain are the same thing.

Fig. 10.1, p. 246

Fig. 10-3, p. 247

(a) Compression causes shortening of rock layers by folding or faulting.

(b) Tension lengthens rock layers and causes faulting.

(c) Shear stress causes deformation by displacement along closely spaced planes. Stepped Art

The Basin and Range Province is a vast physiographic region, result of tensional stresses, defined by a topographic characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins

Tension lengthens rock layers and causes faulting.

FAULTS

 Folded Rock Layers

Figure 10.8, p. 254

FOLDS

Syncline: A fold in rocks in which the rock layers dip inward from both sides toward the axis

Anticline: A fold of rock layers that slope downward on both sides of a common crest.

 Folded Rock Layers  Domes and basins

 Domes and basins are circular to oval structures which have rock layers occurring in age-position contexts which are the same as anticlines and synclines, respectively.

Fig. 10.13a, c, p. 257