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Folds, Faults, and Mountains Pencil Rubber band Gum Foam sediments Cardboard fault models Plastic box Food coloring Paper Begin Chewing Gum.

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Presentation on theme: "Folds, Faults, and Mountains Pencil Rubber band Gum Foam sediments Cardboard fault models Plastic box Food coloring Paper Begin Chewing Gum."— Presentation transcript:

1 Folds, Faults, and Mountains Pencil Rubber band Gum Foam sediments Cardboard fault models Plastic box Food coloring Paper Begin Chewing Gum

2 Fold and Thrust Mountains Enormous mountain ranges form when plates converge.Enormous mountain ranges form when plates converge. Contorted rocks show the power of plate tectonics.Contorted rocks show the power of plate tectonics. Formerly horizontal layers are twisted, bent, or broken.Formerly horizontal layers are twisted, bent, or broken. Some folded rocks are pushed over on their sides, or even upside down.Some folded rocks are pushed over on their sides, or even upside down. Evidence of Lateral Compression

3 Convergent Plate Boundaries and Folding Continent-Ocean collision forms Continental Arc: Andes Cascades. Continent-Continent collision forms Folded Mountain Belt:Alps, Himalayans, Appalachians

4 Compression, tension and shear forces stress the rocks, causing them to strain i.e. “give” Convergent Divergent Transform Units of Stress Force / Area

5 Relation ship Between Stress and Strain Strain can be a change in shape (a deformation) due to an applied stress Rubber Band

6 Relationship Between Stress and Strain at low Temps and Pressure or Sudden Stress Ruler, Pencil

7 Relationship Between Stress and Strain under high Temps or Pressure Chewing Gum

8 Strike and Dip Strike intersection w horizontal, dip perpendicular, angle from horizontal down toward surface Map Symbols: Strike shown as long line, dip as short line. Note the angle of dip shown: 45 o

9 Folded Rocks, Hwy 23 Newfoundland, New Jersey Source: Breck P. Kent Adjacent Anticline and Syncline Note highest point Foam Strata

10 Folded Rocks (Dorset, England) Center has overturned area Source: Tom Bean Lucky we have ways of recognizing right side up What are they? OlderYounger Overturned Area Older Younger Foam strata

11 Folded Rock Before Erosion

12 Folded Rock After Erosion Eroded Anticline, older rocks in center. Syncline is opposite.

13 Topography may be opposite of Structure Anticline Before/After Erosion Notice center rock oldest

14 Topography may be opposite of Structure Syncline Before/After Erosion Notice center rock youngest

15 Various Folds

16 Various Folds (cont'd)

17

18 Axial plane near axis should be close to horizontal Axis

19 Plunging Folds Nose of anticline points direction of plunge, syncline nose in opposite direction Up End Down End Demo: Plastic box, water, paper folds

20 Plunging Folds Source: GEOPIC©, Earth Satellite Corporation Nosed folds, therefore plunging

21 3-D: Dome and Basin

22 Interpreting Folds Determine if center rocks are older or younger than flanks: fossils, right side up clues (graded bedding and mudcracks) Are limbs parallel or “Nosed”? Determine limb dips from measurements, stream V’s. Strike and Dip Use nose rules for anticlines and synclines

23 Fractures Source: Martin G. Miller/Visuals Unlimited Fractures - Joints: fractures with no relative movement - Faults: fractures with relative movement

24 Dip-Slip Faults Demo: Cardboard Models

25 Source: John S. Shelton Normal Fault: Hanging Wall Down Hanging wall overhangs the fault plane Especially common in divergent margins Foot wall under the fault plane Hanging wall is down KEY BED

26 Dip Slip Faults Younger Miners pay geologists to find their lost orebody One friend earned enough to buy a house This poor guy is out of luck What phase of magma fractionation would result in the placement of this ore body? Which formed first, the ore body or the fault? What common mineral is mostly likely in the ore body? This guy is rich Normal Reverse

27 Fracture Zones and Slickensides a)Visible displacement of rocks b)Pulverized rock and “Slickensides” c)Key beds cut out by faulting reappear elsewhere.

28 Types of Faults - 2 Strike-slip faults Strike-slip faults 1)Example: San Andreas Transform fault 2)Distinctive landforms (linear valleys, chains of lakes, sag ponds, topographic saddles) 3)Fresh pulverized rock. Transform fault through granite: Arkose sandstone 4)Evidence of Shear stress

29 Horizontal Movement Along Strike-Slip Fault

30 Faults & Plate Tectonics Divergence Convergence Transform

31 Plate tectonics and faulting Normal faults: mid-ocean ridges and continental rifts are the same thing. Divergent Margins –Surface rock is pulled apart –Hanging wall drops down

32 Horst and Graben Formation

33 Graben in Iceland Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.

34 Plate tectonics and faulting Shallow dipping Reverse Fault called a “Thrust Fault”. Reverse and thrust faults: convergent plate boundaries Hanging Wall is pushed up.

35 Lewis Thrust Fault

36 Lewis Thrust Fault (cont'd) Same layer

37 Lewis Thrust Fault (cont'd) Source: Breck P. Kent PreCambrian Limestone over Cretaceous Shales

38 Plate tectonics and faulting c)Strike-slip faults: Transform Boundaries

39 San Andreas Fault

40 Types and processes of mountain- building (Orogenesis) 1.Volcanic mountains 2.Fold-and-thrust mountains 3.Fault-block mountains 4.Upwarped mountains

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42 Types of Mountains 2. Fold-and-thrust mountains –Formed by Continent-Continent Collisions

43 Appalachian Mountain System

44 The Grand Tetons in Wyoming Source: Peter French/DRK Photo Mostly high angle normal faults ~9mya

45 Fault-block mountains Rift Valleys, Mid Ocean Ridges Basin and Range province ??? Normal Fault Blocks as in East Africa Divergent Margins? Paradigm Shifts

46 Origin of the Basin and Range Southwestern North America Looks different We will discuss Buoyant subduction later

47 Upwarped mountains a)Gently bent without much deformation b)Ascent of buoyant mantle material c) Far from plate boundaries d)Adirondack Mountains: Uplift of deep PreCambrian Igneous and Metamorphic rocks

48 The Adirondack Mountains of Northern New York Source: Clyde H. Smith/Allstock/Tony Stone Images

49 Anticlines and Oil Early USA petroleum exploration, e.g. Pennsylvania anticlines

50 Faults and Oil


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