Mountain Building Orogenesis

1
Mountain Building - Orogenesis
2
Archimedes principle

• The mass of the water displaced by the block of
  material equals the mass of the whole block
• Thus for a material with a lower density than
  water, the proportion of material above the water
  surface is constant
• For example wood (density 0.8 gm/cm) will have
  20 of its mass above water (density of 1.0
  gm/cm). Thus for a 1 m block 0.2 m will be above
  water and 0.8 m below, but for a 2 m block .4 m
  will be above water and 1.6 m below

Fig. 6.28
3
Isostasy
Fig. 6.30
4
Isostasy Mountain Roots

• Continental Crust has roots
• As a result of isostacy, the thicker the surface
  exposure of rock, the thicker the crustal roots
• As continental crust is compressed it shortens
  and thickens
• Avg. continental crust is 35-40 km thick, under
  deformed crust avg. is 50-70 km, with the
  majority of the difference in the roots

Fig. 6.29
5
Isostasy Mountain Roots
Fig. 6.31
6
Class Assignment
Place the following in the appropriate location
on the concept map. Not all terms will be
included and each may be used only once. a)
volcanoes b) Normal faults c) Transform
boundary d) Folds e) Convergent boundary f)
Mountains g) Hot spots h) Divergent boundary i)
Tension stress j) Compression stress k) Shear
stress l) Reverse faults
1
Occur at
Occur along
Occur along
3
2
4
Creating
Creating
Magma Produces
5
7
6
Resulting in
Resulting in
Resulting in
10
8
9
7
Mountain-Types

• Fault-Block Mountains
• Formed from tensional stress
• Normal Faulting
• Example Basin and Range Provinces SW USA

8
Mountain-Types

• Upwarped Mountains
• Formed from compressional stress
• Broad arching of the crust or great vertical
  displacement along faults
• Example Black Hills SD

9
Mountain-Types

• Folded Mountains
• Formed from compressional stress
• Reverse Faulting and Folding highly deformed
  rocks
• Will have highly metamorphosed rocks
• Example Appalachians, Himalayas

10
Mountain-Types

• Volcanic Mountains
• Formed volcanic activity
• Associated with plate boundaries or hot spots
• Example Cascade Mts. Or mountains within Japan

11
Mountain Building (Orogenesis) Zones

• Convergence Zones
• Continental Collision
• Continental Rifting

12
Convergence Zones

• Oceanic-Continental
• Folded Mt. Belts
• Thrust Faults
• Volcanic Chains
• Accreted Terranes
• Example Andes Mountains, Cascades

13
Accreted Terranes

• As exotic blocks collide with continents they
  become sutured to the continent.
• The blocks are referred to accreted terranes
• Accreted Terranes are island arcs, portions of
  ocean floor, fragments of continental crust

14
Convergence Zones

• Oceanic-Oceanic
• Volcanic Chains
• Examples Japan, Philippines

15
Collision Zones

• Folded Mt. Belts
• Thrust Faults
• Remnants of Volcanic Chains
• Examples Alps, Himalayas

16
Continental Rifting

• Fault-block mountains

17
Mountain Building Multiple Events
Example Appalachian Mountains
18
Mountain Building, Rock Cycle and Plate Tectonics
19
Why does the Earth have mountains of various
height?

• Erosion attacks mountains remember Earth wants
  to be flat
• Orogenic collapse.