Chapter 11 Rock Deformation MIDTERM- NOVEMBER 14 BRING A SOFT PENCIL FINAL EXAM DEC.17,12:00 GOLD GYM Chapter ll: Rock Deformation or what you always wanted to know about folds, faults, and joints Stress- the force applied to a plane divided by the area of the plane lithostatic compressive tensile shear tress applied forces directed forces directed stress that equ fr om acts parallel anotner one another to a plane
1 Chapter 11 Rock Deformation MIDTERM ñ NOVEMBER 14 ñ BRING A SOFT PENCIL! FINAL EXAM DEC. 17, 12:00 GOLD GYM Chapter 11: Rock Deformation or what you always wanted to know about folds, faults, and joints Stress = the force applied to a plane divided by the area of the plane. lithostatic compressive tensile shear stress applied equally forces directed toward one another forces directed away from one another stress that acts parallel to a plane
Rock Deformation The change in volume or shape of an object that results from stress is called strain The response of rocks to stress can be divided into elastic response: rock returns to original shape ductile or plastic response: permanent deformation without fracture occurs above the SO-called elastic limit brittle response: fracturing of a rock with little deformation prior to its rupture Rock Deformation The propagation of seismic waves through rocks is an elas- tic response, since the rocks return to their original shape. Ductile(plastic)response of rock layers results in folds permanent wavelike deformations in layered rocks Brittle response to stress results in faults=a fracture in bedrock along which rocks on one side have moved relative to the other side. Where such movement is absent. the fracture is called a joint(several joints=joint sets The rock response to stress is influenced by a number of factors: type of stress, type of rock, temperature, pressure, fluids, length and magnitude of stress applied
2 Rock Deformation The change in volume or shape of an object that results from stress is called strain. The response of rocks to stress can be divided into - elastic response: rock returns to original shape - ductile or plastic response: permanent deformation without fracture; occurs above the so-called elastic limit - brittle response: fracturing of a rock with little deformation prior to its rupture Rock Deformation The propagation of seismic waves through rocks is an elastic response, since the rocks return to their original shape. Ductile (plastic) response of rock layers results in folds = permanent wavelike deformations in layered rocks Brittle response to stress results in faults = a fracture in bedrock along which rocks on one side have moved relative to the other side. Where such movement is absent, the fracture is called a joint (several joints = joint sets) The rock response to stress is influenced by a number of factors: type of stress, type of rock, temperature, pressure, fluids, length and magnitude of stress applied
Rock Deformation The direction of the line formed by the intersection of a horizontal plane with a bedding/fault plane is called strike. The angle formed by the intersection of a bedding/fault plane and the horizontal plane measured in a vertical plane perpendicular to the strike is called dip The symbol used by geologist to display strike and dip on a map is the following: Orientation of planar features in space Fig.11.6
3 Rock Deformation The direction of the line formed by the intersection of a horizontal plane with a bedding/fault plane is called strike. The angle formed by the intersection of a bedding/fault plane and the horizontal plane measured in a vertical plane perpendicular to the strike is called dip. The symbol used by geologist to display strike and dip on a map is the following: 45 Fig. 11.6 Orientation of planar features in space
Rock deformation Folds A fold consist of two limbs which are divided by an imaginary surface called axial plane. The line formed by the intersection of the axial plane and the surface o a rock laver is the fold axis Anticline is a fold with the convex side upward (therefore oldest layers in the middle Syncline is a fold with the concave side upward (therefore youngest layers in the middle) Usually anticlines and synclines alternate in the field. Folds A plunging fold can create interesting map patterns Anticline .Beds are bowed upward . Older beds in core of fold Can be"symmetrical"or asymmetrical
4 Rock Deformation Folds A fold consist of two limbs which are divided by an imaginary surface called axial plane. The line formed by the intersection of the axial plane and the surface of a rock layer is the fold axis. Anticline is a fold with the convex side upward (therefore oldest layers in the middle) Syncline is a fold with the concave side upward (therefore youngest layers in the middle) Usually anticlines and synclines alternate in the field. Folds Anticline ïBeds are bowed upward ïOlder beds in core of fold ïCan be ìsymmetricalî or ìasymmetricalî A plunging fold can create ìinterestingî map patterns
Folds Ine . Beds are bowed downward . Younger beds in core of fold Can be"symmetrical'or asymmetrical Anticline, syncline and the" parts"of folds Fia.11.7
5 Folds Syncline ïBeds are bowed downward ïYounger beds in core of fold ïCan be ìsymmetricalî or ìasymmetricalî Fig. 11.7 Anticline, syncline and the ìpartsî of folds