Chapter 11notes
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Chapter 11notes Presentation Transcript

  • 1. Chapter 11 Mountain Building
  • 2. Rock Deformation
    • It is theorized that all continents were once mountainous masses and grow by adding mountains to their edges.
    • If this is so, then how do mountains grow in the middle of continents?
  • 3. Factors Affecting Deformation
    • Every rock has a point at which it will bend and/or break.
    • Deformation is the term that refers to all changes in the original shape and/or size of a rock body.
    • Most deformation occurs at plate margins.
  • 4.
    • Stress is the force per unit area acting on a solid. Under great stress, rocks tend to deform usually by:
    • Folding
    • Faulting
    • Flowing
    • Fracturing
  • 5.
    • The change in shape or volume of a body of rock as a result of stress is called strain .
    • Rocks can be bent into folds if stress is applied gradually and not going beyond the breaking point.
    • We already know that rocks under stress have elastic properties and will go back to their original shape and size when the force is removed. (elastic rebound)
  • 6.
    • Once the elastic limit or strength of a rock is surpassed, it either flows or fractures .
  • 7.
    • The factors that influence the strength of a rock and how it will deform include:
    • Temperature
    • Confining pressure
    • Rock type
    • Time
  • 8. Temperature and Pressure
    • Rocks deform permanently two ways:
    • Brittle deformation
    • Ductile deformation
  • 9.
    • Rocks near the surface, where temperatures and confining pressures are low, usually behave like brittle solids and fracture once their strength is exceeded.
    • This type of deformation is called brittle failure or brittle deformation .
    • Examples: china, bones, pencils, glass
  • 10.
    • At depth, where temperatures and confining pressures are high, rocks show ductile behavior.
    • Ductile deformation is a type of solid-state flow that produces a change is size and shape of an object without fracturing the object.
    • Examples: modeling clay, bee’s wax, caramel candy, and most metals
  • 11. Question ????????????
    • Placing a penny on a railroad track and having a train run over it, causing the penny to flatten out is an example of?
    • ductile deformation
  • 12. Rock Type
    • The mineral composition and texture of a rock also affect how it will deform.
    • Granite and basalt contain minerals with strong internal molecular bonds will fracture .
    • Sedimentary rocks that are weakly cemented or metamorphic rocks that are foliated are more likely to deform by ductile flow .
  • 13.
    • Rocks that exhibit ductile flow may include:
    • Soft
    • Halite (rock salt)
    • Gypsum
    • Shale
    • Intermediate strength
    • Limestone
    • Schist
    • Marble
  • 14. Time
    • Natural stress applied over a long period of time will fold rocks.
    • Forces that are unable to deform rock when first applied may cause rock to flow if the force is maintained over a long period of time .
  • 15. Types of Stresses
    • Three types of stresses rocks undergo include:
    • Tensional forces – rocks being pulled in opposite directions
    • Compressional force – rocks are squeezed and shortened
    • Shear stress – when a body of rock is distorted
  • 16. Stresses
  • 17. Folds
    • During mountain building, flat lying rocks (both sedimentary and igneous) are bent in wave-like ripples called folds .
  • 18.
    • There are three types of folds:
    • Anticline – an upward fold (arch)
    • Syncline – a downward fold (trough)
    • Monocline – closely associated with faults, monoclines are large step–like folds in otherwise horizontal layers of sedimentary strata.
    • Prominent features of the Colorado Plateau which coves Colorado, New Mexico, Utah, and Arizona.
  • 19. Anticline and Syncline Process
  • 20.  
  • 21. Circular Anticline
  • 22. Syncline
  • 23.  
  • 24.  
  • 25.
    • Joints – fractures in rock strata where no movement has taken place
    • So faults are……………
  • 26.  
  • 27. Three types of faults
    • Normal – caused by tensional stress
    • Reverse (or thrust) – caused by compressional stress
    • Strike-slip – commonly caused by shear stress – San Andreas Fault
  • 28. Normal
  • 29. Reverse or Thrust
  • 30. Strike-Slip
  • 31. What type of fault?
    • Strike-slip
  • 32. What type of fault?
    • Normal
  • 33. What type of fault?
    • Reverse or Thrust
  • 34.  
  • 35.  
  • 36. Thrust fault
  • 37. Types of Mountains
    • The collective processes that produce a mountain belt are called orogenesis .
    • The dominant processes that have formed them classify mountains.
  • 38. Folded Mountains
    • Mountains formed primarily by folding are called folded mountains .
    • Thrust faults are also important in the formation of folded mountains.
    • These mountains are called fold and thrust belts .
    • Examples: Appalachian Mountains, the northern Rocky Mountains, and the Alps of Europe
  • 39.  
  • 40. Fault-Block Mountains
    • Large-scale normal faults are associated with structures called fault-block mountains.
    • These mountains form when large blocks of crust are uplifted and tilted along normal faults . 
    • Examples: Teton Range of Wyoming and the Sierra Nevada Range of California.
  • 41.  
  • 42.
    • Normal faulting occurs when tensional stresses cause the crust to be stretched or extended.
    • As the crust is stretched, a block called a graben , which is bounded by normal faults, drops down.
    • Graben is German for ditch or trench.
    • Grabens produce an elongated valley bordered by relatively uplifted structures called horsts .
    • Examples: Basin and Range Province of Nevada, Utah, and California.
  • 43.  
  • 44.  
  • 45. Rift or Grabben
  • 46.
    • Graben or Rift
    • example is: Death Valley 250 ft. below sea level
    Dead Sea is 1200 ft below sea level
  • 47. Domes and Basins
    • These mountains are produced by broad upwarping in the basement rock deforming the overlying sedimentary strata.
    • A dome is when upwarping produces a circular or elongated structure or dome .
  • 48.
    • How are these domes uncovered?
    • Erosion strips away the highest portion of the sedimentary beds exposing older igneous and metamorphic rocks in the center.
    • The oldest rocks form the core of these mountains. 
    • Example: Black Hills
  • 49.
    • Downwarped structures having a circular shape are called basins .
    • These structures have gently sloping bed similar to saucers.
    • Basins are thought to be formed by the accumulation of sediment, whose weight caused the crust to subside .
    • Example: Basins of Michigan & Illinois
    • In the case of a basin the oldest rocks are found in the center with the youngest rocks on the flanks.
  • 50.  
  • 51. Mountain Formation
    • Just how old are mountains?
    • Appalachians are 100s of million of years old
    • Himalayas are about 45 million years old… Just a youngster!
  • 52. Mountain Building at Convergent Boundaries
    • Most mountain building occurs at convergent plate boundaries.
    • Colliding plates provide the compressional forces that fold, fault, and metamorphose the thick layers of sediment deposited on the edges of landmasses.
  • 53. Ocean-Ocean Convergence
    • Converging oceanic plates result in subduction that creates magma leading to the growth of a volcanic island arc once it grows above sea level.
    • Examples: Aleutian Islands in Alaska, Japan,
    • Ocean-ocean convergence mainly produces volcanic mountains.
  • 54.  
  • 55.  
  • 56.  
  • 57. Ocean-Continental Convergence
    • Example: West coast of South America – the Andes Mountains
    • This produces a continental volcanic arc .
    • During subduction, sediment scraped from the subducting plate is stuck against the landward side of the trench.
    • This accumulation of sediment and metamorphic rock is called an accretionary wedge .
  • 58.
    • Ocean-continent convergence produces mountains in two roughly parallel belts.
    • The continental volcanic arc develops on the continental block and the accretion wedge is on the seaward belt.
    • The types of mountains formed by ocean-continent convergence are volcanic mountains and folded mountains .
  • 59.  
  • 60. Continent-Continent Convergence
    • A convergent boundary between two plates carrying continental crust, a collision between the continental fragments will result and form folded mountains .  
    • Example: Himalayan Mountains and the Tibetan Plateau, European continent collided with Asia producing the Ural Mountains in Russia.
  • 61.  
  • 62. Mountain Building at Divergent Boundaries
    • These mountains are usually formed on the ocean floor
    • Example: Mid-ocean ridges that extend 65,000 kilometers.
    • The mountains that form along ocean ridges at divergent plate boundaries are fault-block type mountains.
  • 63.  
  • 64. Non-Boundary Mountains
    • Example: Hawaiian Islands
    • Continental Accretion
    • Accretion is when small crustal fragments collide and merge with continental margins.
  • 65.  
  • 66.
    • Terrane – is any coastal fragment that has a geological history distinct from that of the adjoining terranes.
    • Some may be no larger than volcanic islands, while other are immense, such as the entire Indian subcontinent.
    • Some may have been microcontinents similar to present day Madagascar.
    • Many others were island arcs like Japan and the Philippines.
  • 67.
    • All these materials add to the continent width and thickness displacing other fragments further inland.
  • 68.  
  • 69. Mountains of Accretion
    • Example: Mountains in western North America and western Canada contain rock, fossils, and structures different from the surrounding area.
    • These materials have been accreted (added to) the western margin of North America.
  • 70. Principle of Isostasy
    • This is a gradual up and down motion of materials that make up the interior of continents away from continental margins.
    • Earth’s crust floats on top of denser more flexible rocks in the mantle.
    • The concept of a floating crust in gravitational balance is isostasy .
  • 71.
    • Mountain belts float on top of more dense crustal roots that extend into the mantle.
    • The denser mantle supports the mountains from below.
  • 72.
    • If more material were added to the top of the mountains the combined block would sink until a new isostatic balance was reached.
    • However, the top of the combined block would be higher than before and the bottom would be lower.
    • This process of establishing a new level of gravitational equilibrium is called isostatic adjustment .
  • 73.  
  • 74.  
  • 75. Isostatic Adjustment of Mountains
    • Continental ice sheets provided evidence of crustal subsidence followed by rebound.
    • The weight of 3 kilometers of ice depressed Earth’s crust by hundreds of meters.
    • In 8000 years since the last ice sheets melted, uplift of as much as 330 meters has occurred in Canada’s Hudson Bay region.
  • 76.
    • Most mountain building causes the crust to shorten and thicken.
    • Because of isostasy, deformed and thickened crust will undergo regional uplift both during mountain building and for a long period afterward.
    • As the crust rises (rebounds) the processes of erosion increases and the deformed rock layers are carved into mountains.
  • 77.
    • Erosion removes material from the summit reducing the load causing the crust to rise. This will continue until the mountain block reaches its “normal” thickness.