GEOL 213 Final, Fall 1997

Geology 213: Structural Geology Final Exam Fall 97/98 Time allowed: Two hours Exam rules apply Section A (60 marks) Answer this section on the sheet provided. Note that three marks will be given for a correct answer and one mark will be deducted for an incorrect answer Figure | B _- c D _ SFE ——— Fa LE. ZA = The sense of shear demonstrated by the structures A-D in figure is: All are dextral All are sinistral A and B are dextral. C and D are sinistral A and C are dextral, D and B are sinistral A, B and D are dextral, C is sinistral Fi 2 gure 2a Figure 2a is a picture of a cube before deformation and figure 2b is a picture afler deformation. ‘The deformation is best described as being a product of : Simple shear Simple shear and yolume change Simple shear and homogeneous strain Volume change and homogeneous strain Volume change, homogeneous strain and simple shear r wy WIGAN UNTwrne ry The S -surfaces in a Type | S-C fabric are: LIBRARY A strain sensitive fabric parallel to the S1/S2 plane of the strain ellipse Lote eed | A strain sensitive fabric parallel to the S1/S3 plane of the strain ellipse A shear band parallel to the $1/S3 plane of the strain ellipse A strain insensilive fabric parallel to the $1/S2 plane of the strain ellipse A strain insensitive fabric parallel to the $1/S3 plane of the strain ellipse or Al a Nye) S1 50 So eaten Figure 3 N SO 4. The relationships shown between bedding So and cleavage Si in figure 3 are indicative of which of the following: a. A scries of overturned folds which verge to the north b. A series of overturned folds which verge to the south c. Asyncline, anticline pair which verge in different directions d. A periclinal fold plunging north e. The data is contradictory and more information is required to give a correct answer Figure 4. 4a 4b 5. Figure 4a shows a reference circle and two perpendicular lines prior to deformation Figure 4b shows the resultant strain ellipse. Which of the following statements is true: a. The style of deformation responsible for the strain ellipse is simple shear, line e underwent +38° of angular shear and line f underwent -38° of angular shear. b. The style of deformation responsible for the strain ellipse is simple shear, line ¢ underwent -38° of angular shear and line f underwent +38° of angular shear. c. The style of deformation responsible for the strain ellipse is pure shear, line e underwent +38° of angular shear and line f underwent -38° of angular shear. d. The style of deformation responsible for the strain ellipse is simple shear, tine e underwent -38° of angular shear and line f underwent +38° of angular shear. e. None of the above Figure 5. 6. The fold shown in figure 5 is made up of a series of layers. Each layer has a different isogon pattern. Using the isogons the folds can be best classified as: a. A= Class 1A, B = Class 2, C = Class IC b. A=Class 1C, B= Class 2, C = Class 3 c. A=Class 1C, B= Class 3, C = Class 2 d A= Class 2, B = Class 1B, C = Class 1C ce. A= Class 3, B = Class 2, C = Class IB 7 a. b. c. d. e enoge eaooe » epnogpe . Which of the following are not linear structures Rodding Stretched pebble conglomerate Mullions Pencil structure Chocolate tablet boudinage . LS tectonites are best described as: A product of flattening that transforms an original sphere into an oblate strain ellipsoid. Magnitudes of the finite strain ellipse are S1=S2>S3. A product of flattening that transforms an original sphere into a prolate strain ellipsoid. Magnitudes of the finite strain ellipse are S1=S2>S3. A product of unidirectional stretching that transforms an original sphere into a prolate strain ellipsoid. Magnitudes of the finite strain ellipse are S1>S2=S3. A product of stretching in one direction compensated by flattening at right angles to the direction of stretching with neither stretching nor shortening in the intermediate direction that transforms an original sphere into a triaxial strain ellipsoid. Magnitudes of the finite strain ellipse are S1>S2=S3 where S2=0. A product of stretching in one direction compensated by flattening at right angles to the direction of stretching with neither stretching nor shortening in the intermediate direction that transforms an original sphere into a triaxial strain ellipsoid. Magnitudes of the finite strain ellipse are $1>S2>S3 where §2=1. Mechanical conditions that favour passive folding are: High mean ductility and low ductility contrast High mean ductility and high ductility contrast Low mean ductility and low ductility contrast Low mean ductility and high ductility contrast Moderate mean ductility and low ductility contrast Figure 6. 10. The fibres shown in figure 6 are best described as: Syntaxial a product of coaxial deformation Composite a product of coaxial deformation Syntaxial a product of dextral non-coaxial deformation Antitaxial a product of sinistral non-coaxial deformation Insufficient evidence has been given for you to describe the fibres with accuracy. 11. Which of the following is not an example of continuous cleavage: A= slaty cleavage, B=schistosity, C= Phyllitic structure, D= Crenulation cleavage, E=Spaced cleavage. A only Band C Cand D DandE D only Figure 7. 12. The R and P shears shown in diagram 7 are a product of: Dextral shear in an E-W oriented strike-slip zone Dextral shear in an N-S oriented strike-slip zone Sinistral shear in an E-W oriented strike-slip zone Sinistral shear in an N-S oriented strike-slip zone Dextral shear in an NE-SW oriented strike-slip zone sao8 13. The magnitude of slip on a thrust fault is 7km. The lengih of the next lower thrust stice is 7km. The result is: A normal duplex A forward duplex An antiformal stack A hinterland dipping duplex +6, A foreland dipping duplex sao tp / Figure 8. a 8 (Ov 3 \ \ “6 \ N +o 9. ) k "\ G, N AK Gy. 6g ~ \ a (Tensile) Ne ee (Compressive) -6, 14. Figure 8 is a Mohr stress diagram representing which of the following: a. Differential stress b. Hydrostatic stress c. Uniaxial stress d. Axial stress e. Triaxial stress Yield Stress Figure 9 Stress (o) Strain Rate (€) 15. Figure 9 is: a. A portrayal of ideal viscous behaviour A portrayal of ideal plastic behaviour A portrayal of Hooke’s law None of the above All of the above aos €. 16. Which of the following statements regarding Mohr failure envelopes are true: a. b. Cc. d. €. Figure 10 oe = critical shear stress required for faulting oo = cohesive strength To = tensile strength ¢ = angle between the fracture surface and the direction of greatest principal stress 3. @= angle of internal friction * All of the statements are true Only 1, 2 and 3 are true Only 2, 3 and 5 are true 1, 2, 3 and 5 are true. 4 is false 2, 3 and 4 are true. 1 and 5 are false. RYN 17. Figure 10 shows a strain ellipsoid divided into four sectors A, B, C and D. Which of the following a. l a. b. c. d. €. Statements regarding figure 10 is correct? The strain ellipse is the result of progressive pure shear. A represents instantaneous and finite shortening, B represents finite shortening but instantaneous extension, C represents finite and instantaneous extension, D represents finite and instantaneous extension following an initial period of shortening. The strain ellipse is the result of progressive pure shear. A represents finite shortening but instantancous extension, B represents instantaneous and finite shortening, C represents finite and instantancous extension following an initial period of shortening, D represents finite and instantaneous extension. The strain ellipse is the result of progressive simple shear. A represents finite shortening but instantaneous extension, B represents instantaneous and finite shortening, C represents finite and instantaneous extension following an initial period of shortening, D represents finite and instantaneous extension, The strain ellipse is the result of progressive simple shear. A represents instantaneous and finite shortening, B represents finite shortening but instantaneous extension, C represents finite and instantaneous extension, D represents finite and instantaneous extension following an initial period of shortening. The strain ellipse is the result of progressive pure shear. A represents instantaneous and finite shortening, B represents finite shortening but instantaneous extension, C represents finile and instantaneous extension following an initial period of shortening, D represents finite and instantaneous extension. Assuming pure shear and a simple relation between stress and strain which of the following is true? G1 should be parallel to S1 33 should be parallel to S3 G1 should be parallel to S3 01 should be 45° to $3 None of the above 19. Coble creep is best defined as: Dislocation creep Superplastic creep Pressure solution Grain boundary diffusion creep Dissolution creep Figure 11 Tensile ‘A | Failure Envelope 20. Figure 11 shows a coulomb failure envelope. To begin with o1 and o3 are both compressive with low differential stress, but when the pore fluid is raised the result is: The stress circle crashes into the tensile failure envelope and the rock breaks by Mode 1 failure, a. b. The stress circle crashes into the parabolic failure envelope and the rock breaks though transitional tensile failure. The stress circle crashes into the parabolic failure envelope and breaks according to Coulomb’s law of failure in the compressive field The stress circle crashes into the frictional sliding envelope and breaks through transitional tensile behaviour. Nothing Section B (20 marks) NAMle......ceccesereeee Using labelled diagrams explain: (a) what is meant by the following and (b) the processes that led to their development 1. Microcracks 2. Dissolution creep 3. Structural inversion +. Fault-bend folds 5. Foliation fish Section C (20 marks) Using labelled diagrams explain what the result would be in each of the following cases: Jornal Faulling P Undeformed 3. Strongly foliated rock \ A — Strain ellipse w