Lecture Intro Deformation Sp23 PDF

F F Youngest J M A D X O B Oldest Mountain Building and Plate Tectonics Mountain building poorly understood before Plate Tectonics. Pre-Plate Tectonics (wrong) idea: Earth’s crust contracted and “crinkled up” like a dried apple skin....

F F Youngest J M A D X O B Oldest Mountain Building and Plate Tectonics Mountain building poorly understood before Plate Tectonics. Pre-Plate Tectonics (wrong) idea: Earth’s crust contracted and “crinkled up” like a dried apple skin. Plate Tectonics Perspective: Mountains due to collision or extension (and volcanoes). Rock Deformation Deformation: Any process that effects the size, shape, or volume of an area of Earth’s crust.  Components of Deformation Deformation can have several components, Including: 1) Displacement 2) Rotation 3) Distortion or Strain Marshak, Essentials Components of deformation Displacement Marshak, Essentials Components of deformation Rotation Marshak, Essentials Components of deformation Distortion or strain Can have more than one type of deformation Marshak, Essentials Why do rocks deform?....... The same reason any other material will: Force. Plate Tectonics subjects crust to tremendous forces! Three phases material goes through when increasing force is subjected. Marshak, Essentials Three phases material goes through when increasing force is subjected. Marshak, Essentials Three phases material goes through when increasing force is subjected. Marshak, Essentials  Force vs Stress It is often more useful to geologists to talk about stress than force. Marshak, Essentials  Force vs Stress It is often more useful to geologists to talk about stress than force. Stress = Force per unit area. Marshak, Essentials  Stress Force versus stress Stress: force per unit area Types of stress Compression Tension Shear Pressure Marshak, Essentials  Stress Force versus stress Stress: force per unit area Types of stress Compression Tension Shear Pressure Marshak, Essentials  Stress Force versus stress Stress: force per unit area Types of stress Compression Tension Shear Pressure Marshak, Essentials  Strain Strain: Change in size or shape resulting from application of force. (One aspect of deformation). Marshak, Essentials  Types of strain Original Marshak, Essentials  Types of strain Original Marshak, Essentials  Types of strain Original Marshak, Essentials  Types of strain Original Marshak, Essentials  Types of strain Original Marshak, Essentials Materials Deform Differently Different materials will deform differently under the same conditions, and the same material will deform differently under different conditions What matters? Material, Pressure & Temperature Types of Deformation Brittle Deformation vs Ductile Deformation Brittle deformation Cold (geologically speaking) Low pressure Marshak, Essentials Brittle deformation Cold (geologically speaking) Low pressure Fast/sudden Rock strength Strong – granite vs Weak – halite Marshak, Essentials Ductile deformation Warm/hot High pressure Marshak, Essentials Ductile deformation Warm/hot High pressure Slower Rock strength Strong – granite vs Weak – halite Marshak, Essentials Ductile deformation Warm/hot High pressure Slower Rock strength Strong – granite vs Weak – halite Depth in continental crust brittle 10-15 km Marshak, Essentials  How are rocks deformed? Ductile Deformation Brittle Deformation Brittle Deformation Marshak, Essentials Brittle deformation Joints Fractures/cracks in rock Usually linear, repeated No movement/sliding along joints Caused by tensional (or tensile) stress Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Marshak, Essentials Brittle deformation Joints Fractures/cracks in rock Usually linear, repeated No movement/sliding along joints Caused by tensional (or tensile) stress Veins: joints filled with minerals (quartz or calcite) Potential engineering challenge Marshak, Essentials Brittle deformation Veins Marshak, Essentials Brittle deformation Veins Marshak, Essentials Brittle deformation Veins Marshak, Essentials Brittle deformation Faults Fractures where sliding occurred Active/inactive Surface/depth Marshak, Essentials Brittle deformation Faults Fractures where sliding occurred Active/inactive Surface/depth Marshak, Essentials  Brittle deformation Faults Fractures where sliding occurred Active/inactive Surface/depth Marshak, Essentials Brittle deformation Faults Marshak, Essentials Brittle deformation Faults Marshak, Essentials  Types of Faults Brittle Deformation Faults Normal Thrust/Reverse Strike- slip Tension Compression Shear  Faults: dip-slip Reverse/thrust: >30 deg/30 deg/30 deg/