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Ch 15 (Part I): Crustal deformation Today:

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Ch15 (Pt I): Crustal Deformation 1) Deformation 2) Mapping geologic structures 3) Folds

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Chapter 15: Crustal deformation Examines forces that deform rock & resulting structures Why do we care? u geological past u oil & natural gas u metal ores u building locations (hazards)

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1) Folds 2) Faults 3) Joints 4) Rock cleavage 5) Foliation Chapter 15: Crustal deformation Basic geologic structures associated w/ deformation: Chapter 7 Metamorphic Rocks Been there, done that

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1) Deformation F Stress F Strain force applied to a rock deformation of rock from the applied stress

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1) Deformation: Stress Confining pressure: force equal in all directions Differential stress: force not equal in all directions

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Brittle deformation rocks crack/fracture Ductile deformation rocks flow Shallow in crustDeeper down 1) Deformation: Stress Confining pressure: force equal in all directions Differential stress: force not equal in all directions

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1) Deformation: Stress Confining pressure: force equal in all directions Compressional stresses: shortening Differential stress: force not equal in all directions

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1) Deformation: Stress Confining pressure: force equal in all directions Compressional stresses: shortening Tensional stresses: elongation Differential stress: force not equal in all directions T&L Figure 15.4

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Compressional stresses: shortening Tensional stresses: elongation Shear stresses: bending (shearing) 1) Deformation: Stress Confining pressure: force equal in all directions Differential stress: force not equal in all directions T&L Figure 15.4

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2) Mapping geologic structures Deformational processes create faults folds, joints rock structures Visible when rock beds are exposed at surface out crops

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2) Mapping geologic structures F Strike and dip Strike Dip trend relative to north, measured as an angle angle of tilt of a bed

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3) Folds u series of wavelike bending of once-flat rock layers u many sizes: microscopic to 100’s of meters ucompressive stresses: shorten+thicken crust

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3) Folds u series of wavelike bending of once-flat rock layers u many sizes: microscopic to 100’s of meters ucompressive stresses: shorten+thicken crust

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3) Folds F Types of folds F Other deformations anticline - arching hill of layers syncline - trough of layers monocline - one-limbed fold dome - circular upwarping basin - circular downwarping hogbacks - erosion-resistance strata

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hogbacks Strata resistant to erosion

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