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Earth Sciences
Earth Sciences 1022A/B
Stephen R Hicock

Earth Sciences 1022a Lecture Brief 10 Oct 13 CRUSTAL DEFORMATION Rocks can be deformed to produce structures that can yield energy and ore reserves Deformation: when rocks are stressed beyond their strength they change shape, size compressional stress squeezes rocks and shortens Earth’s crust, tensional stress stretches and lengthens crust, shear stress causes sideways slip of crust strain is what happens to rocks being stressed (stress is the force, strain the result) - starts with elastic deformation where no permanent damage occurs but after stresses pass the rock’s elastic limit (strength), permanent damage occurs by brittle deformation that is common near the surface under low P, T conditions, or ductile deformation that is common deep in the crust (under high P, T conditions) - strong rocks tend to fracture while weak rocks tend to flow (in the solid state) however, with enough time even strong brittle rocks will eventually flow Mapping geologic structures: geologists measure rock structures in outcrops, using strike - compass direction of horizontal line on the planar surface of a bed or fault dip – angle of inclination (fall line) of the surface, at a right angle to the strike Folds – due to compressional stress, resulting in shortening, thickening of crust; have limbs on either side of a fold axis, and an axial plane that evenly divides the limbs anticline (arch) and syncline (trough) commonly
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