GLY 101 1st Edition Lecture 17 Outline of Last Lecture II.Modern Bathymetric Techniques III. Continental Margins Features of Deep-Ocean BasinsOutline of Current Lecture II. What Causes Rock to DeformIII. Folds: Rock Structures formed by Ductile DeformationIV. Faults and Joints: Rock Structures formed by Brittle DeformationCurrent LectureII. What Causes Rock to Deform- deformation is a general term that refers to the changes in shape or position of a rock body in response to differential stress.- rock structures or geologic structures are the basic geologic features that form as a result of the forces generated by the interactions of tectonic plates.-rock structures include: folds (wavelike undulations) faults (fractures along which one rock body slides past another) joints(cracks) - stress is the force that deforms rocks- when stress is applied uniformly in all directions this is confining pressure- when stress is applied unequally in different directions this is called differential stressThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- compressional stress is differential stress that squeezes a rock mass as if placed in a vice- tensional stress is differential stress that pulls apart or elongates rock bodies- shear stress is differential stress that involves movement of one part of a rock body past another- when flat-lying sedimentary layers are uplifted and tilted, their orientation change- differential stresses can also change the shape of a rock body or strain- strained bodies lose their original configuration during deformation- three types of deformation: elastic, brittle, and ductile- changes from elastic deformation are coverable - rocks that break into smaller pieces have brittle deformation- ductile deformation is a type of solid stat flow that produces a change in the shape of an object without fracturing -factors that affect rock strength: temperature, confining pressure, rock type and time- compression causes shortening, tension causes stretching, shear distorts rockIII. Folds: Rock Structures formed by Ductile Deformation-anticlines and synclines are two most common types of folds- the up folded or arched structures are anticlines and the down folds or troughs are synclines- the ends of folds are called plunges because the axis of a fold penetrates the earth -symmetrical is when the limbs of the fold mirror each other; asymmetrical do not mirror IV. Faults and Joints: Rock Structures formed by Brittle Deformation-faults form where brittle deformation leads to fracturing and displacement of Earth’s crust-sudden movement in faults are the cause of most earthquakes-some fault surfaces the rocks are polished and striated this is called slickensides- faults in which movement is primarily parallel to the inclination are called dip-slip faults- rock surface immediately above the fault is the hanging wall block; rock surface below is the footwall block-dip slip faults are classified as normal
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