CEE 1030 1nd Edition Lecture 10 Structural Geology Outline of Last Lecture I Structure of an atom II Radioactive decay III Basic principles of isotopic dating IV Methods of radioactive dating V Earth s oldest rocks VI Absolute ages for the Geologic Time Scale VII Volcanic ash layers Outline of Current Lecture I What is structural geology II Mapping geological structures a Investigating the shallow earth III Deformation a Brittle deformation b Ductile deformation Current Lecture I II What is structural geology a Because of plate tectonics continents are constantly colliding creating faults and mountain ranges b 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 falling Mapping geological structures a Field observations by geologists to describe and map orientations and lithology of rock units b Outcrops sites where the bedrock is exposed at the surface c You can use i Aerial photography ii Satellite imagery iii GPS d Strike trend the compass direction of the line is produced by the intersection of inclined rock layer or fault with a horizontal plane These 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 III e Dip inclination the angle of inclination of the surface of a rock unit or fault is measured from a horizontal plane f Investigating the shallow earth i Drilling is expensive and can only get information from one spot ii Seismic reflection sound waves get reflected from boundaries of different rock types Deformation a 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 area c Strain change in rock s shape or size caused by stress d Elastic deformation when rock returns to nearly its original size and shape when the stress is removed i Once elastic limit of rock is exceeded it either 1 Falls brittle deformation use the analogy of a plate dropping and shattering 2 Flows ductile deformation use the analogy of a book dropped on soft dough e Factors of rock deformation i Temperature hotter more elastic ductile ii Confining pressure high pressure ductile iii Rock minerals iv Time more time more elastic f Brittle deformation i Types of rock fracture 1 Joint no appreciable movement across the crack 2 Fault relative movement of rocks on either side of the fracture ii Joints are very common rock structures concentrates effects of chemical weathering iii Sudden movement along fault is known as an earthquake iv Types of faults 1 Dip slip movement is parallel to the dip of fault surface a Hanging wall rock surface above the fault b Footwall rock surface below the fault c Normal dip slip faults accommodate lengthening or extension of the crust d Reverse and thrust dip slip faults i Reverse have dips greater than 45 degrees ii Thrust faults have dips less than 45 degrees accommodate shortening of crust e Strike slip faults dominant displacement is horizontal and parallel g Ductile deformation i Folds during crystal deformation rocks are often bent into series of wave like undulations as compressional stresses shorten and thicken the crust 1 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 faults ii Dome anticlinal structure oldest rocks featured in the center iii Basin synclinal structure youngest rocks in the center
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