Download Mountain Building - Orogenesis

Mountain Building - Orogenesis
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
Isostasy
Fig. 6.30
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
Isostasy &
Mountain Roots
Fig. 6.31
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 along Occur at
Occur along
3
2
Creating
Magma Produces
5
4
Creating
7
6
Resulting in
10
8
9
Mountain-Types
• Fault-Block Mountains
– Formed from tensional
stress
– Normal Faulting
– Example: Basin and
Range Provinces SW
USA
Mountain-Types
• Upwarped Mountains
– Formed from compressional stress
– Broad arching of the crust or great vertical displacement
along faults
– Example: Black Hills SD
Mountain-Types
• Folded Mountains
–
–
–
–
Formed from compressional stress
Reverse Faulting and Folding – highly deformed rocks
Will have highly metamorphosed rocks
Example: Appalachians, Himalayas
Mountain-Types
• Volcanic Mountains
– Formed volcanic activity
– Associated with plate
boundaries or hot spots
– Example: Cascade Mts. Or
mountains within Japan
Mountain Building (Orogenesis)
Zones
Convergence Zones
Continental Collision
Continental Rifting
Convergence
Zones
• Oceanic-Continental
–
–
–
–
–
Folded Mt. Belts
Thrust Faults
Volcanic Chains
Accreted Terranes
Example: Andes Mountains,
Cascades
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
Convergence
Zones
• Oceanic-Oceanic
– Volcanic Chains
– Examples:
Japan,
Philippines
Collision Zones
• Folded Mt. Belts
• Thrust Faults
• Remnants of Volcanic
Chains
• Examples: Alps,
Himalayas
Continental Rifting
• Fault-block mountains
Mountain
Building –
Multiple
Events
Example:
Appalachian
Mountains
Mountain Building, Rock Cycle
and Plate Tectonics
Why does the Earth
have mountains of
various height?
• Erosion attacks
mountains – remember
Earth wants to be flat
• Orogenic collapse.