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Folds, Faults, and Mountain Building Chapter 9.

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Presentation on theme: "Folds, Faults, and Mountain Building Chapter 9."— Presentation transcript:

1 Folds, Faults, and Mountain Building Chapter 9

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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 – 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 – 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

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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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