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What is it?

What is it?. Faults. Homework due today - New homework assignment handout today. Joints: Geometry: planar; plumose structure; joint “sets” Kinematics: walls move apart very slightly in direction of “pull” Mechanics: form by tensile loading; cooling; *removal of overlying rock

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What is it?

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  1. What is it?

  2. Faults • Homework due today - • New homework assignment handout today

  3. Joints: Geometry: planar; plumose structure; joint “sets” Kinematics: walls move apart very slightly in direction of “pull” Mechanics: form by tensile loading; cooling; *removal of overlying rock Other: abundant in uppermost crust

  4. Under compression, rocks fail along shear fractures (sliding motion rather than pulling apart motion) Introduction to Faults (p. 269-279; 286-296)

  5. Fault: Shear fractures along which there is visible offset; generally planar or curviplanar

  6. Strike-slip faults: Accommodate horizontal slip between adjacent blocks; steep (~vertical) faults left lateral (sinistral) right lateral (dextral) left lateral vs. right lateral: sense-of-slip relative to a chosen block

  7. What is it? left lateral vs. right lateral

  8. For faults that are not vertical…. Hanging wall: The block above the fault. Footwall: The block below the fault.

  9. Normal fault: hanging wall moves down with respect to footwall

  10. What is it? Normal faults generally place younger and/or lower-grade rocks (in HW) on top of older and/or higher-grade rocks (in FW) HW young low-grade “dirt” FW old high-grade gneiss

  11. Normal faults generally place younger and/or lower-grade rocks (in HW) on top of older and/or higher-grade rocks (in FW) What is it? Cambrian limestone FW HW Tertiary conglomerate

  12. Purchase a time scale card from SESS – only $1!

  13. Thrust fault (reverse fault): hanging wall moves upward relative to footwall What is it? HW FW

  14. Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW)

  15. Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW)

  16. Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW) What is it? HW sandstone low grade blueschist FW high grade

  17. Normal faults accommodate lengthening

  18. Thrust faults accommodate shortening

  19. http://earth.leeds.ac.uk/learnstructure/index.htm

  20. Slip vs. Separation Slip: ACTUAL relative displacement Separation: APPARENT relative displacement

  21. A natural example demonstrating that apparent separation can be much different than true slip!

  22. The key to describing slip along a fault lies in measuring (1) Direction of displacement (2) Sense of displacement (3) Magnitude of displacement

  23. Listric: curved faults that flatten with depth listric normal fault

  24. Map Symbols: a start • Strike-slip fault • Normal fault • Thrust fault

  25. Next lecture: Intro to folds Read pgs. 372-413

  26. Announcements: Field trip to Cottonwood Canyon this Saturday - meet at 7:45 am at the loading dock! Bring pencils, protractor Will it rain? Rain gear Will it be hot? Sunscreen lotion Hiking boots, water, lunches Will be back around 4 pm.

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