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 There are two kinds of continental margins (boundary between oceanic and continental crust) 1. Margins that are found on plate boundaries (active continental margins) Appalachian Mountains = used to be at a convergent boundary Himalaya Mountains = on a current convergent boundary 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 Feb 19 8:19 AM Feb 19 9:22 AM Jan 10 11:27 AM Jan 10 11:29 AM 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 Jan 10 11:35 AM Feb 19 9:28 AM 1
Normal fault Jan 10 1:17 PM Feb 19 10:00 AM Feb 19 9:59 AM Jan 10 1:15 PM Normal fault Jan 10 1:15 PM Feb 19 8:28 AM 2
Tensional stress cause this rock to create several successive normal faults The hanging wall is the dark basalt on the left (west). The footwall is the sandstone on the right (east). Feb 19 8:26 AM Feb 19 8:27 AM Compressional stress: Rock layers are being squeezed making them shorter and thicker Normal faulting Compressional stress can create reverse faults and folds Feb 19 8:28 AM Feb 19 9:48 AM 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 Feb 19 10:00 AM Feb 19 9:55 AM 3
Chapter 11 mountain building E.notebook Reverse fault Fault plane Feb 19 8:29 AM Feb 19 8:30 AM Reverse fault and folding This thrust (reverse fault) is approximately horizontal...you can see the anticline in the hanging wall and the syncline in the footwall Feb 19 8:31 AM Feb 19 9:55 AM Reverse fault 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 Feb 19 8:32 AM Feb 19 8:31 AM 4
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 Parts of a fold 1. Anticline 2. Syncline 3. Limb 4. Dip 5. Strike Feb 19 12:21 PM Feb 19 12:16 PM Feb 19 9:49 AM Feb 19 9:58 AM Feb 19 9:49 AM Feb 19 9:58 AM 5
Feb 19 9:50 AM Feb 19 9:51 AM Feb 19 9:52 AM Feb 19 9:53 AM Feb 19 8:34 AM Feb 19 8:35 AM 6
Chapter 11 mountain building E.notebook Upright folds Feb 19 8:35 AM Feb 19 8:36 AM Chevron folds Feb 19 8:36 AM Feb 19 8:37 AM Ptygmatic folds Disharmonic folds Feb 19 8:37 AM Feb 19 8:37 AM 7
Chapter 11 mountain building E.notebook 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 Feb 19 8:38 AM Feb 19 12:32 PM Exfoliation joints Feb 19 8:39 AM Feb 19 8:39 AM Exfoliation joints Jointing Feb 19 8:39 AM Feb 19 8:40 AM 8
Joints filled in with minerals Joints filled in with minerals Feb 19 8:40 AM Feb 19 8:40 AM Sheer stress: Involves stress moving in opposite directions away from each other, with little up or down movement Sheer stress creates strike slip faults Feb 19 9:48 AM Feb 19 9:55 AM Strike slip fault Feb 19 10:00 AM Feb 19 8:33 AM 9
Chapter 11 mountain building E.notebook FOLDED TYPES OF MOUNTAINS 1. Folded 2. Volcanic 3. Dome 4. Fault Block 5. Horsts and Grabens Caused 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 Jan 13 11:13 AM Jan 13 11:15 AM Jan 13 11:28 AM Jan 13 11:30 AM DOME 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 Dome mountains are nearly circular folded mountains but do not form in belts. instead they are individual and isolated Examples of dome mountains are the Adirondack mountains of NY and the Black Hills in SD Jan 13 11:30 AM Jan 13 11:35 AM 10
Jan 13 11:43 AM Jan 13 11:45 AM Volcanic Volcanic 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 Jan 13 12:52 PM Jan 13 11:45 AM 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 Jan 13 11:48 AM Jan 13 11:52 AM 11
Jan 13 11:53 AM Jan 13 11:55 AM 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 Jan 13 11:56 AM Feb 19 9:54 AM Jan 13 1:20 PM Jan 13 1:22 PM 12
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