lec 12 13 structure University of （大学的lec 12 13结构）.pdfVIP

GEOLOGIC STRUCTURES GEOLOGIC STRUCTURES Pre-Cordillera: Patagonian Andes, Argentina Pre-Cordillera: Patagonian Andes, Argentina • Stress and Strain • Active deformation along faults • Geologic maps and cross sections • Folding • Faulting GEOLOGIC STRUCTURES GEOLOGIC STRUCTURES “Architecture of bedrock” Architecture of bedrock • Structural Geology- – concerned with shapes, arrangement, interrelationships of bedrock units forces that cause them. • Important to understanding: – How mountains form – How continents evolve – How plate tectonics works – Safe siting of public facilities, dams, power, etc. – Search for energy resources TECTONIC FORCES AT WORK TECTONIC FORCES AT WORK • Stress Strain: • Stress Strain –Stress (force per unit area) • Compressive stress • Compressive – Shortening strain • Tensional stress • Tensional – stretching or extensional strain • Shear stress • Shear – Shear strain –Strain (change in size, shape, during stress) Behavior of rocks under stress Behavior of rocks under stress • Elastic (recovery to original shape) • Elastic – Elastic limit • Beyond this stress, permanent strain • Plastic (ductile) • Plastic (ductile) – Permanent strain by flow, or folding – Typical at higher P, T within crust • Brittle • Brittle – Permanent strain by fracture, failure – Typical at lower P, T near surface – Rocks fracture when strain rates are high Present Deformation of the Crust Present Deformation of the Crust • Active fault fault –Fracture along which movement has occurred rapidly • “Creep” –Slow sustained movement along a f