Chapter 11: Rock Deformation Chapter 11 Rock Deformation or what you always wanted to know abou folds, faults, and joints MIDTERM- NOVEMBER 14 Stress= the force applied to a plane divided by the BRING A SOFT PENCILA area of the plane. compressive tensile shear FINAL EXAM DEC.17,12:00 GOLD GYM Rock Deformation Rock Deformation The propagation of seismic through rocks is an elas- response, since the rocks return to their original shape. The change in volume or shape of an object that results from stress is called strain Ductile(plastic) response of rock layers results in folds permanent wavelike deformations in layered rocks The response of rocks to stress can be divided into Brittle response to stress results in faults= a fracture in elastic response: rock returns to original shape bedrock along which rocks on one side have moved relative ductile or plastic response: permanent deformation to the other side. Where such movement is absent. the without fracture occurs above the fracture is called a joint (several joints= joint sets SO-called elastic limit brittle response: fracturing of a rock with little deformation The rock response to stress is influenced by a number of prior to its rupture factors: type of stress, type of rock, temperature, pressure, nuids, length and magnitude of stress applied Rock Deformation Orientation of planar features in space The direetion of the line formed by the intersection of a Fig.11.6 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
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 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: 45 Fig. 11.6 Orientation of planar features in space
Rock deformation Folds Folds A plunging fold can create A fold consist of two limbs which are divided by an maginary surface called axial plane. The line formed by the intersection of the axial plane and the surface of a rock laver is the fold axis Anticline is a fold with the convex side (therefore oldest layers in the Anticline Syncline is a fold with the concave side m (th Usually anticlines and synclines alternate in the field -Can be"symmetrical"or Folds Anticline, syncline and the "parts of folds Syncline .Beds are bowed downward -Can be"symmetrical"or symmetrical Rock deformation Common fold types Fg.118 Fold Tvpes Fold Types Fold Axis Axial I Limbs dip in ymmetrical F. horizontal vertical opposite directi Asymmetrical F. horizontal inclined opposite directior different angles recumbent over turned Overturned Fold horizontal inclined same direction unbent Fold horizontal horizontal same direction urging Folds inclined
2 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 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 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.11.12 Plunging anticline syncline pairs Note the"V outcrop pattern Fia. 11 Monoclines MIDTERM- NOVEMBER 14 BRING A SOFT PENCIL A sudden steepening in an otherwise gently dipping Fig.11.14 FINAL EXAM DEC.17,12:00 GOLD GYM Ba Rock deformation Domes and basins are rounded versions of synclines Fractures and anticlines Domes: anticlinal cireular structure Fracture Direction of Dip Angle synclinal circular structure Types Displacement Normal Fault Hanging >45 degree 1g.11.14 (dip slip fault Reverse Fault Hanging wall up dip slip fault) Thrust faul Hanging wall up <45 degree (dip slip fault) Strike-slip Faulthorizontal (strike slip fault)
3 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 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. 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 Movement on Faults and terminology Foot wall block below faul) above Strike Slip= AC Dip slip CB Throw AE Fig.11.19 Heave= ED Net Slip AB true horizontal Kinds of Faults Normal Fault hrust Fault . Movement on hanging wall is .Fault plane very low angle Result of extensio .Common Fault type in Foothills and Rockies Strike sp Fault Reverse Fault Movement or wall is up Plate Tectonic Settings and Topographic Features Plate Tectonic Settings and Topographic Features trike-Slip Faults or transform faults form long linear valleys usually indicated by streams or long lakes Usually in rift zones where the crust stretched Note"Drag"of beds along fault(what kind of deformation is this?) Fig.11.22
4 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 Kinds of Faults Normal Fault ïMovement on hanging wall is down relative to footwall ïResult of extension Reverse Fault ïMovement on hanging wall is up relative to footwall ïResult of compression Strike- slip Fault Thrust Fault ïSpecial case of reverse fault ïFault plane very low angle ïCommon Fault type in Foothills and Rockies Plate Tectonic Settings and Topographic Features Strike-Slip Faults or transform faults form long linear valleys usually indicated by streams or long lakes Plate Tectonic Settings and Topographic Features Usually in rift zones where the crust stretched. Note ìDragî of beds along fault (what kind of deformation is this?) Normal Faults Fig. 11.22
Plate Tectonic Settings and Topographic Features Plate Tectonic Settings and Topographic Features Normal Faults Normal Faults. extension in the crust. rifts Ranges are uplifted blocks (horsts)and basins are down thrown n and range topography often caused by heating of deep crust Fg.11.25 Fg.11.26 Plate Tectonic Settings and Topographic Features Crustal shortening Chief Mtn. Montana Thrust Faults in regions subject to compressive Similar structures stress(colliding plate boundaries) along Hiway 3 YOU LIVE NEAR ONE OF THE BEST EXPOSED THRUST SEQUENCES ON EARTH: Also Castle Mtn (#1and#93) CALGARY MORLEY Shortening" in Rockies to west is about 80km Fg.1128 Fig.11.29
5 Plate Tectonic Settings and Topographic Features Ranges are uplifted blocks (horsts) and basins are down thrown blocks (grabens). Normal Faults Fig. 11.25 Plate Tectonic Settings and Topographic Features Basin and range topography often caused by heating of deep crustal rocks. Normal Faults - extension in the crust - rifts Fig. 11.26 Plate Tectonic Settings and Topographic Features Thrust Faults in regions subject to compressive stress (colliding plate boundaries) YOU LIVE NEAR ONE OF THE BEST EXPOSED THRUST SEQUENCES ON EARTH! CALGARY MORLEY LAKE LOUISE CANMORE BANFF Fig. 11.28 Crustal Shortening Fig. 11.29 Chief Mtn, Montana Similar structures along Hiway 3 Also Castle Mtn (#1 and #93) ìShorteningî in Rockies to west is about 80km
