CEE 1030 1nd Edition Lecture 10: Structural GeologyOutline of Last Lecture I. Structure of an atomII. Radioactive decayIII. Basic principles of isotopic datingIV. Methods of radioactive datingV. Earth’s oldest rocksVI. Absolute ages for the Geologic Time ScaleVII. Volcanic ash layersOutline of Current Lecture I. What is structural geology?II. Mapping geological structuresa. Investigating the shallow earthIII. Deformationa. Brittle deformationb. Ductile deformationCurrent LectureI. What is structural geology?a. Because of plate tectonics, continents are constantly colliding, creating faults andmountain rangesb. Structural geology: the study of rocks and their geometry (deformation, faults, etc)c. It is important for building roads, etc, to see the probability of rocks sliding and fallingII. Mapping geological structuresa. Field observations by geologists to describe and map orientations and lithology of rock unitsb. Outcrops: sites where the bedrock is exposed at the surfacec. You can use:i. Aerial photographyii. Satellite imageryiii. GPSd. Strike (trend): the compass direction of the line is produced by the intersection ofinclined rock layer or fault with a horizontal planeThese 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.e. Dip (inclination): the angle of inclination of the surface of a rock unit or fault is measured from a horizontal planef. Investigating the shallow earthi. Drilling is expensive and can only get information from one spotii. Seismic reflection: sound waves get reflected from boundaries of differentrock typesIII. Deformationa. Deformation is the general term for all changes in the original form or size of a rock unit (most common: folding, faulting)b. Stress: force applied to a particular areac. Strain: change in rock’s shape or size caused by stressd. Elastic deformation: when rock returns to nearly its original size and shape when the stress is removedi. Once elastic limit of rock is exceeded, it either:1. Falls (brittle deformation): use the analogy of a plate dropping andshattering2. Flows (ductile deformation): use the analogy of a book dropped on soft doughe. Factors of rock deformationi. Temperature (hotter=more elastic, ductile)ii. Confining pressure (high pressure=ductile)iii. Rock mineralsiv. Time (more time=more elastic)f. Brittle deformationi. Types of rock fracture1. Joint: no appreciable movement across the crack2. Fault: relative movement of rocks on either side of the fractureii. Joints are very common rock structures, concentrates effects of chemical weatheringiii. Sudden movement along fault is known as an earthquakeiv. Types of faults1. Dip-slip: movement is parallel to the dip of fault surfacea. Hanging wall rock surface above the faultb. Footwall rock surface below the faultc. Normal dip-slip faults accommodate lengthening or extension of the crustd. Reverse and thrust dip-slip faultsi. Reverse have dips greater than 45 degreesii. Thrust faults have dips less than 45 degrees, accommodate shortening of cruste. Strike-slip faults: dominant displacement is horizontal and parallelg. Ductile deformationi. Folds: during crystal deformation, rocks are often bent into series of wave-like undulations as compressional stresses shorten and thicken the crust1. Synclines and anticlines form from folds (anticlines fold upward, look like the letter A)2. Monoclines: large, step-like folds in otherwise horizontal sedimentary strata, often the result of buried faultsii. Dome: anticlinal structure, oldest rocks featured in the centeriii. Basin: synclinal structure, youngest rocks in the