STRUCTURAL GEOLOGY     I. STRUCTURAL GEOLOGY A. Structural geology--deformation of earth materials B. Deformation--change in shape and/or volume C. Distortion--shape change = constant volume D. Dilation--change in volume E. Stress = force/area = pressure, kilobars, psi F. Strain = result of stress 1. Strain is a unitless measure, strain unit, percent strain 2. Rock deformation apparatus--vise a. Rxs are stronger than the vise b. Time c. Rock strength--highest stress a rx can withstand 3. Elastic = recoverable strain 4. Plastic = nonrecoverable strain a. Flow ~ plastic deformation 5. Mechanisms of plastic deformation a. Mechanical dislocations b. Recrystallization c. Intergranular flow--grains rotate and slide past one another 6. 4 types of stress a. Tensional--pulling apart b. Compressional--pushing together c. Shear (or rotational) stresses--deal with shear couples d. Hydrostatic stress--stress comes from all directions, what a sub feels ~ lithostatic G. Strike--bearing of a horizontal line on an inclined plane 1. Read from 2 northern quadrants H. Dip--the maximum angle of inclination of a plane measured perpendicular to strike 1. Ranges from 0o = horizontal to 90o = vertical II. ATTITUDE OF STRUCTURES A. Planar structures B. Axis--line of maximum curvature on a folded surface C. Axial surface--connection of all the fold axes D. Types of folds 1. Anticline--concave down, oldest units in middle 2. Syncline--concave up, youngest units in middle 3. Plunging anticline a. Contact v's point in direction of plunge 4. Plunging syncline a. Contact v's open in direction of plunge 5. Dome--doubly-plunging anticline e.g. Nashville dome 6. Basin--doubly-plunging syncline e.g. Michigan basin 7. Overturned fold--one limb is overturned 8. Monocline--has 1 limb 9. Recumbent fold--horizontal axial surface 10. Isoclinal fold--limbs have the same orientation III. FAULTS A. Hanging wall B. Footwall C. Types of faults 1. Normal faults a. Dip-slip fault b. Hanging wall moves down relative to footwall c. Emplaces younger rocks on older rocks d. Tensional stresses e. Extends and thins crust f. Example mid-ocean ridges, western U.S., Basin and Range~100%, East African Rift System 2. Reverse faults a. Dip-slip fault b. Hanging wall moves up relative to footwall c. Emplaces older rocks on younger rocks d. Compressional stress e. Shortens and thickens crust f. Thrust faults--type of reverse fault that dips < 30o Thrust sheets--thin sheets of rx moved by thrust faults (~1km thick, 100 km wide, ~2000 km long) g. Example Talladega thrust, AL; Glarus thrust, Switzerland 3. Strike-slip faults a. Right-lateral e.g. San Andreas b. Left-lateral c. Conserves thickness and area of crust D. Joints--fractures with little (< 1cm) or no movement along them 1. Joint sets--parallel joints 2. Joint system--2 or more joint sets a. Joints form at nearly any point in the history of a rock b. Ground water movement in crystalline rxs 3. Two types of Joints a. Columnar Joints - form due to tensional stresses during cooling of a lava b. Exfoliation - process of producing sheets or slabs of rx due to erosional unroofing of homogeneous rx e.g. Stone Mtn., GA