Structural Geology

1. Structural Geology R. B. Schultz

2. Structural Geology Guiding Principles: • Rocks below the earth's surface are hot and tend to flow • (ductile flow) • Rocks at / near surface are relatively cool and tend to be more brittle • (fracture ).  

3. Structural Geology Definitions:  Deformation: general term: change in rock shape / volume / fabric, etc. Stress -- force that causes deformation Strain-- result of the stress applied; ie., the specific deformation Types of stresses : 1.     Extension or tension (pulling apart) 2.    Compression (pushing together) 3.    Shearing or twisting (one portion in one direction, the other portion in another direction)

4. Responses to stress: 1.     Ductile deformation -- usually deeper and with higher temperatures; flow 2.    Brittle deformation -- usually shallower and with cooler temperatures; fracture Ductile deformation produces folds: 1.     Anticline -- upwarping of rocks to produce an "A-like" structure 2.    Syncline -- downwarping of rocks to produce "spoon-like" structure 3.    Dome -- three-dimensional anticline resembling inverted cereal bowl 4.    Basin -- three-dimensional syncline resembling upright cereal bowl *When brittle deformation occurs and rocks fracture, they can simply crack producing a fracture with no offset, called a joint. When brittle deformation occurs and rocks fracture, they can also crack producing a fracture with offset (shift) called a fault.

10. There are four (4) major faults types in two (2) categories: • 1.       Dip-slip faults: associated with vertical motion • Normal fault -- produced from tensional forces • Reverse fault-- produced from compressional forces • 2.     Strike-slip faults: associated with horizontal motion • Right-lateral strike-slip fault – as you look across the fault line the block on the other side shifts to your right. • Left-lateral strike-slip fault – leftward shift

15. Geologists must have a way of orienting the rock formations such that they can be visualized in a horizontal as well as a vertical frame of reference. The measurement of rock unit orientation is called its attitude (orientation). Strike -- measurement of horizontal attitude in relation to true north on a map. Dip -- measurement of vertical attitude as unit trends into the earth. These two (2) components are always presented in the following notation: Strike: N (degrees< 90o) E or W Where: Degrees measurement refers to the degrees deviating from north Direction (E or W) refers to the direction it is deviating towards Dip: (degrees< 90o) direction | to strike Where: Degrees measurement refers to the degrees from horizontal ground surface trending into the earth Direction is always perpendicular to strike direction *This system is always written in the shorthand notation as above. Example: N 25o E, 13o NW means that the horizontal trend is 25 degrees east of north (strike) and dips 13 degrees from the horizontal into the earth (dip).

16. Key Terminology Deformation Stress Strain Extension Compression Shearing Ductile Brittle Anticline Syncline Dome Basin Joint Fault Normal fault Reverse fault Dip-slip fault Strike-slip fault Right-lateral strike-slip fault Left-lateral strike-slip fault Strike Dip Attitude

17. Pertinent Web Sites Active Tectonics Web Server The Active Tectonics Web Server was established in order to effectively disseminate ideas resulting from the Active Tectonics initiative. Fault Animations Excellent animations of faults, plate subduction, earthquake wave propagation, and other processes from PBS' Savage Earth program. Folds, Faults, and Mountain Links (Houghton Mifflin) Links to several folds, faults, and mountain building sites, including class lecture notes, arranged by topic. Geology Search Gallery The University of British Columbia Image Gallery contains images related to the earth and ocean sciences, including some specialized subsets (e.g., Lithoprobe, Structural Geology). Grand Teton National Park Field Trip An illustrated walking trip through parts of Grand Teton National Park, including the geology of the area. Hayward Fault A walking tour of California's Hayward Fault. Mountain Building Activity (Geosphere) An excellent interactive activity on mountain building from the University of Montana's Geosphere. With this activity learners identify major mountain ranges, formation processes, and utilize plate tectonics to explain geologic formations. National Parks Links Links to all U.S. National Parks arranged alphabetically by name. Structural Block Diagrams by Stephen J. Reynolds Block diagrams illustrating various types of inclined bedding and how geology is expressed in the landscape.

18. Structural Geology and Tectonics Division (GSA) The Geological Society of America (GSA) Structural Geology and Tectonics Division home page includes links to several related sites. Structural Geology and Tectonics Groups An alphabetical listing of university research groups in structural geology by country. Structural Geology Links (NAGT) A listing of structural geology links from the National Association of Geology Teachers. Structural Geology on the Web A great site to begin your investigation of a folds and faults. Structural Geology Tutorial Structural geology tutorial from Texas A & M University. Structures Page, The This page contains great information, images, and links to information on structural geology.