Mountain Building - Orogenesis. Archimedes’ principle Fig. 6.28 –The mass of the water displaced...
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Transcript of Mountain Building - Orogenesis. Archimedes’ principle Fig. 6.28 –The mass of the water displaced...
Mountain Building - Orogenesis
Archimedes’ principle
Fig. 6.28
– 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. 6.30
Isostasy
Isostasy & Mountain Roots
Fig. 6.29
– 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. 6.31
Isostasy & Mountain Roots
Class Assignment
1
2 4
5 7
6
108 9
Occur along Occur along
Creating Creating
Resultin
g in
Resulting in
Resulting in
Occur at
3
Magma Produces
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) volcanoesb) Normal faultsc) Transform boundaryd) Foldse) Convergent boundaryf) Mountainsg) Hot spotsh) Divergent boundaryi) Tension stressj) Compression stressk) Shear stressl) Reverse faults
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 ZonesContinental CollisionContinental 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.