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
Rock Deformation Fold Types Fold Types Fold Axis Axial Limbs dip in Planes ymmetrical F. horizontal vertical opposite direction equal angles Asymmetrical F. horizontal inclined opposite directio different angles Overturned Fold horizontal inclined same direction Recumbent Fold horizontal horizontal same direction Plunging Folds inclined Common fold types Fig.11.8 symmetrical asymmetrical recumbent over turned
6 Rock Deformation Fold Types Symmetrical F. horizontal vertical opposite direction equal angles Asymmetrical F. horizontal inclined opposite direction different angles OverturnedFold horizontal inclined same direction Recumbent Fold horizontal horizontal same direction Plunging Folds inclined Fold Types Fold Axis Axial Limbs dip in Planes Common fold types Fig. 11.8 symmetrical over turned asymmetrical recumbent
The"plunge"of a fold is the angle between the fold axis and the horizontal within the axial plane Fig.11.11 1g.11.12 Plunging anticline-syncline pairs Note the V outcrop pattern
7 Fig. 11.11 The ìplungeî of a fold is the angle between the fold axis and the horizontal within the axial plane Fig. 11.12 Plunging anticline-syncline pairs Note the ìVî outcrop pattern
MIDTERM- NOVEMBER 14 BRING A SOFT PENCILA FINAL EXAM DEC.17,12:00 GOLD GYM Monoclines A sudden steepening in an otherwise gently dipping strata is called a monocline Fig.11.14
8 MIDTERM ñ NOVEMBER 14 - BRING A SOFT PENCIL! FINAL EXAM DEC. 17, 12:00 GOLD GYM Monoclines A sudden steepening in an otherwise gently dipping strata is called a monocline. Fig. 11.14
Domes. basins Domes and basins are rounded versions of synclines and anticlines D omes anticlinal circular structure Basin: synclinal circular structure Fia.11.14 Rock Deformation Fractures Fracture Direction of Dip angle Types Displacement Normal Fault Hanging wall down>45 degree (dip slip fault) Reverse fault Hanging wall up 45 degree (dip slip fault) Thrust fault Hanging wall up 45 degree (dip slip fault) Strike-slip Fault horizontal 0 degree (strike slip fault
9 Domes, Basins Domes and basins are rounded versions of synclines and anticlines. Domes: anticlinal circular structure Basin: synclinal circular structure Fig. 11.14 Rock Deformation Fractures Normal Fault Hanging wall down > 45 degree (dip slip fault) Reverse Fault Hanging wall up > 45 degree (dip slip fault) Thrust Fault Hanging wall up < 45 degree (dip slip fault) Strike-slip Fault horizontal 0 degree (strike slip fault) Fracture Direction of Dip Angle Types Displacement
Terms to describe faults ig Movement on Faults and terminology Foot wall Hanging wa∥ (block below fault) (block above fault) Strike Slip Ac Dip Slip= CB Throw= AE true vertical D Net slip AB Heave = ED true horizontal
10 Fig. 11.19 Terms to describe faults Movement on Faults and terminology A B C E D Net Slip = AB Strike Slip = AC Dip Slip = CB Throw = AE true vertical Hanging wall (block above fault) Foot wall (block below fault) Heave = ED true horizontal
