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Folds, Faults, and Mountain Building

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Presentation on theme: "Folds, Faults, and Mountain Building"— Presentation transcript:

1 Folds, Faults, and Mountain Building
Chapter 9


3 Stress!!! Stress—a force exerted on an object Rocks react to stress by
Deforming plastically Deforming elastically Breaking by brittle fracture Question of the hour (#1) How will a particular rock react to a particular stress?

4 It’s all in the Nature… Rock composition
Ex: Hitting a chunk of concrete with a sledgehammer VS. hitting a giant rubber tire with a sledgehammer

5 I Can’t Take the Pressure!!
Pressure and Temp. increase with depth Temp vs. pressure Burial promotes plastic deformation

6 If you can’t stand the heat…
Higher temperatures favor plastic deformation Ex. Bending a steel nail Need to be super strong Or just heat the thing up…

7 It’s About Time… Stress applied slowly favors plastic behavior
Stress applied suddenly favors brittle behavior

8 May the Tectonic Force be With You….
Plate tectonic forces Tensional Stretch and pull formations apart Compressive Squeeze and shorten rock formations Shearing Two sides of a formation are pushed in opposite directions (sliding past one another)

9 Geologic Structures Plate tectonics—primary stressor
3 main types of structures Folds—ductile deformation (primarily) Faults—brittle deformation Joints—brittle deformation

10 Folds A fold is a bend in the rock Three characteristics
Plastic deformation Three characteristics Usually results from compression Folding always shortens the horizontal distances in rock A fold usually occurs as part of a group of folds

11 Anticline Vs. Syncline

12 Plunging Folds

13 Overturned and Asymmetric

14 Circular Features Domes Basin
Circular anticlinal structure (both pics) Beds dip away from center Basin Circular synclinal structure Beds dip towards center

15 All My Faults are Stress Related!!!
Brittle deformation Faults Cracks in rock along which motion has occurred Movement may be gradual or sudden (earthquake) Usually associated with other faults in a fault zone Question of the hour (#2): Why do rocks move repeatedly along faults and fault zones?

16 Nature is Lazy Rock moves repeatedly along faults and fault zones because Tectonic forces often affect one location for a long time It’s easier Three types of faults Depend on tectonic forces

17 Normal Faulting

18 Reverse Fault (part 1)

19 Reverse Fault (part 2)

20 Strike-slip Fault

21 Ah, How My Joints Ache… A joint is a fracture in rock along which no motion has occurred Planes of weakness—like mineral cleavage Good for mining

22 Styles of Continental Deformation
Relating Small Structures to Big Picture

23 Question of the Hour (#3)
Where do mountains come from? In a subducting zone Magmas/lavas—stall/erupt High temp—rocks expand when heated Continent/continent collision—underthrusting Crust is shoved under other crust Compression squeezes crust—thickness increases

24 Tensional Tectonics Plates can split apart
Rift valleys – long narrow troughs formed by a block that has dropped down between two big normal faults

25 Rifting and Normal Faulting


27 Compressive Tectonics
Fold and thrust belts: When two continental plates collide, crust compressed Crust thickened by underthrusting—thicken crust 2x

28 Transverse Margins

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