Chapter 11 mountain building E.notebook...Chapter 11 mountain building E.notebook 3 December 21,...
Transcript of Chapter 11 mountain building E.notebook...Chapter 11 mountain building E.notebook 3 December 21,...
Chapter 11 mountain building E.notebook
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Mountains form along convergent plate boundaries. Typically (usually) if you look at a mountain range, you know that it is at a plate boundary (active continental margin) or has been some time in the past
Appalachian Mountains = used to be at a convergent boundary
Himalaya Mountains = on a current convergent boundary
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There are two kinds of continental margins (boundary between oceanic and continental crust)
1. Margins that are found on plate boundaries (active continental margins)
2. Margins that are found within a plate (passive)
Both contribute to the building of mountains but in different ways. Passive margins only add accumulated sediment built up on the edge of a continent over hundreds, thousands, or millions of years and won't contribute to creating a mountain until the boundary becomes active
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Stress is the force that deforms rocks. Mountains form when rocks are permanently deformed from stress. There are three primary kinds of stress.
1. Tension (pulling) this will make a rock thinner and longer
Tensional stress creates normal faults. Normal faults occur when the hanging wall falls down in relation to the foot wall
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Normal fault
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Normal fault
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Tensional stress cause this rock to create several successive normal faults
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The hanging wall is the dark basalt on the left (west). The footwall is the sandstone on the right (east).
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Normal faulting
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Compressional stress: Rock layers are being squeezed making them shorter and thicker
Compressional stress can create reverse faults and folds
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Compression can make a type of reverse fault called a thrust fault if the fault plain is 45 degrees or less from the horizontal plane
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Reverse fault
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Fault plane
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This thrust (reverse fault) is approximately horizontal...you can see the anticline in the hanging wall and the syncline in the footwall
Reverse fault and folding
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Chief mountain is a good example of how faulting can create peaks. The hanging wall is the prominent peak. The footwall is the dark shale covered in vegetation
Reverse fault
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Compression can cause folding of rock if it is deep in the ground (warmer) or the rock is ductile. Folds can also occur if the stress is exerted slowly over a very long period of time
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Parts of a fold
1. Anticline2. Syncline3. Limb4. Dip5. Strike
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Upright folds
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Chevron folds
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Ptygmatic folds
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Disharmonic folds
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Joints are cracks in rocks that have no movement along the plain of the crack.
Joints can be caused by several factors...
1. Rebound of rock that has been compressed
2. swelling or shrinking of rock layers
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Exfoliation joints
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Exfoliation joints
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Jointing
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Joints filled in with minerals
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Joints filled in with minerals
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Sheer stress: Involves stress moving in opposite directions away from each other, with little up or down movement
Sheer stress creates strike slip faults
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Strikeslip fault
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TYPES OF MOUNTAINS
1. Folded2. Volcanic3. Dome4. Fault Block5. Horsts and Grabens
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FOLDEDCaused by continental collision
Folded mountains have characteristic anticlines and synclines
Evidence of some volcanic activity is typical, and this occurs when the oceanic basin is being subducted under the continent before the collision of the two converging continents occurs.
Sediment that has build up on the passive continental margin is also pushed up during collision to adds to the material forming the folded mountains
Examples of folded mountains are the Himalayan and the Appalachian mountains
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DOME
Dome mountains are nearly circular folded mountains but do not form in belts. instead they are individual and isolated
Dome mountains can occur from uplifting forces in the ground or from plutonic activity (like a laccolith) pushing up overlying flat layers
* plutonic dome* tectonic dome
Examples of dome mountains are the Adirondack mountains of NY and the Black Hills in SD
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VolcanicVolcanic mountains tend to form on continental crust near a subduction boundary
Andes Mountains are an example on the western side (oceanic material is subducting below the South American continent) of South America
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FAULT BLOCK Tensional stress on rocks produce normal faults which can result in the formation of fault block mountains
The tension responsible for the formation of fault block mountains comes from uplift
Examples of fault block mountains are the Sierra Nevada range in California and the Wasatch Range in Utah
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HORSTS AND GRABENS
Caused by tensional stress and normal faulting
Caused from the stretching of tectonic plates.
Examples are the great rift valley in Africa (where the continent is being ripped apart) and the Basin and range province in NV
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