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.