Chapter 9 Mountain Building

9-1    Crustal Uplift:

1. Some features shouldn't be seen now if no crustal uplift:

   • Fossils in rocks

   • High elevation of wave cutting platform

2. Isostasy:

   • When plates float on top of surface, part of the thickness underneath it, e.g. floating wood blocks in water. the thicker, the higher.

   • Continental crust thick in mountain ranges, thus deep also. The crust is thick in Rocky Mountains compared to that in Wisconsin.

3. Isostasy adjustment:

   • As erosion persist, uplift occurs. Fig. 9.4.

   • AA: jagged shape. Fig. 8.4b. Relative high viscosity, low T.

9-2    Rock Deformation:

1. Elastic vs. plastic: Elastic when force removed, the deformation disappear. Deformation permanent for plastic, e.g. clays.

2. Folds: due to compressional force.

   

   • Anticline: center older

   • Syncline: center younger

   • Axis: normally horizontal. If tilted: plunging anticline or plunging syncline. Fig. 9.8.

   • Fold plane: symmetrically if fold plane vertical. Asymmetric. Overturned: both tilted to one direction. Fig. 9.6.

   • Domes vs. basins: The length and width ~ equal, showing spheric feature. Dome: center old. Basin: center young.

3. Faults: Fracture with displacement.

   

   • Normal fault: hanging wall moves downward, due to tensional force.

   • Reverse fault: hanging wall moves upward, due to compressional force.

   • Strike-slip fault: horizontal displacement, due to shearing force.

   • Horst and graben: symmetric normal or reverse faults on both sides.

   

4. Joint: fracture but no displacement. Follow certain patterns.

9-3    Mountain types:

Classified based on structural properties:

1. Fault block mountains: 

   • Formed by tensional forces.

   • Characters: have normal faults on one side at least.

   • Example: Basin and Range Provinces, Teton, Sierra, Nevada.

   • Cause: Upwelling of magma, caused by sliding of two plate slabs. Fig. 9.16.

2. Folded mountains: 

   • Folding is more obvious, other activities present, too.

   • Examples: Alps, Hamalaya, Urals.

   • Formed by compressional forces.

   • Detail in Next section.

3. Upwarped mountains:

   • Formed by broad arching of the crust.

   • Examples: Black Hill, Adirondacks.

   • Character: contain exposed old igneous and metamorphic rocks. Fig. 9.18.

9-4    Mountain Building:

1. Orogenesis: Mountain building process, mainly limited to folding mountains, due to compressional nature, always associated with contact between places.

2. When an oceanic crust meets with a continental crust along continental margin - Andes types

   1. Passive stage: Fig. 9.21A.

      • No volcanic activity

      • thick deposition of sediments

      • no subduction zone

   2. Active stage: Fig. 9.21B.

      • subduction zone forms

      • deformation begins

      • volcanic arc begins to form

      • accretionary wedge begins to form

   3. Two mountain zones form:

      • landward part: intrusive igneous rock, metamorphic rock

      • seaward part: sedimentary rocks with high degree of deformation.

      • Examples: Sierra Navada: inner and Coast Range: outer.

3. When an oceanic crust meet with an oceanic crust - Aleutian type.

   • Similar to CO/CC, but the upper plates will eventually evolve into continental crust. Fig. 9.20a-b.

4. When a continent crust meet with a continental crust - Himalaya type.

   • Collision occur instead of subduction.

   • Create even thick crust.

   • Present example: Alps and Himalaya.

   • Past example: Urals.

5. Continental accretion:

• Small pieces of crustal fragments collide to continental margin and attached there. 

• Fossils, magnetic properties, rock type differ among continental and terranes, indicating terranes are foreign source.

• Examples: CA coast.

Homework:

• Read chapter summary on p.267.

• Use your own word to explain the key terms on page 267

• Answer the review questions on page 268.