Mountain Orogeny

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Mountain Orogeny
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Three types of plate boundary
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ORIGIN OF MOUNTAINS

• Orogeny process of mountain building, takes
  tens of millions of years usually produces long
  linear structures, known as orogenic belts

Two main processes 1) Deformation continental
collisions, resulting in
folding and thrust-faulting 2) Volcanic
Activity Other processes Metamorphism,
intrusions batholiths, etc.
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TYPES OF MOUNTAINS(according to their origin)

• Fault-block tension, normal faulting
• ex. Sierra Nevada, Wasatch, Grant Tetons
• Folded compression, reverse faulting
• ex. Appalachians, Alps, Himalayas, Urals, Atlas,
  Andes
• Volcanic Shield and composite
• ex. Cascades, Mid-Ocean Ridges, Oceanic Hot
  Spots
• Dome Mts similar to volcanic, Adirondacks,
  Black Hills
• Complex mixture of most of the above
• ex. Rockies, Alps, Himalayas

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Organization of Mountains

• Every mountain is part of a 
• Mountain Range (ie. Green Mountains, Great Smoky,
  Blue Ridge, the Cumberland, White Mountains)
• groups of ranges make up a 
• Mountain System (ie. Northern Appalachian Mts.)
• groups of systems make up 
• Mountain Belts (ie. Appalachian Belt)

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1. Fault-block mountains large areas widely
broken up by faults
Normal fault

• Force TENSION
• Footwall moves up
• relative to hanging
• wall

HANGING WALL
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Tilted fault-block range Sierra Nevada from
east, Steep side of block fault Ansel Adams photo
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Tilted Fault-block Sierra Nevada from west Side,
low angle Yosemite valley the result Of
glaciation on low-angle relief
Central cores consists of intrusive igneous
rocks (granite). Half Dome is a core
(batholith) that was exposed by erosion,
Batholith
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Wasatch Range From Salt Lake City Typically
fault- Block system
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Grand Tetons another fault-block system
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Horst and graben
Alternating normal faults lead to a
characteristic pattern called a horst and
graben system. An area under tension will often
have multiple mountain ranges as a result.
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Horst and Graben Landscapes
Figure 12.14
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Basin and Range province

• tilted fault-block
• mountains in Nevada
• result of a horst and
• graben system
• Nevada is under tension
• because of rising magma
• which is unzipping the
• system, all the way from
• Baja California

Sierra Nevada and Wasatch Ranges part of this
system
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Reverse faults can also form Fault Block Mts.

• Force COMPRESSION
• Hanging wall moves up
• relative to footwall
• Two types
• -low angle
• -high angle

Individual layers can move 100s of
kilometers Alps are a great example
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Flatirons (Boulder, CO) Classic example of
high-angle reverse faults -gt Form Sawtooth
Mtns due to differential erosion
Seal rock
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SAWTOOTH RANGE, IDAHO Alice Lake
White Cloud peak
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Folded mountains

• Thrust (reverse) faults main
• cause of folded mountains

• Where rock does not fault it folds,
• either symmetrically or asymmetrically.

upfolds anticlines downfolds synclines
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Classic folded terrain well-developed anticline
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Appalachian Mountains of the US
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Atlas Mountains, Northern Africa
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Zagros Crush Zone (Iran/Iraq)
Alternating Anticlines and Synclines
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Volcanic mountains

• Shield
• Gradual slope, very tall to ocean floor, slow
  flowing eruptions, composed of layers of lava
• Composite (Strato-)
• Explosive, made of pyroclastic material and lava.
  steep
• Cinder cone  
• Very steep slopes, made of pyroclastic material,

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Types of Volcanic Material

1. Pyroclastic material rock fragments ejected from
   volcano
2. Ash less than 2 mm in diameter
3. Dust less than .25 mm diameter
4. Bombs spinning cooling large blocks of
   material, cool to circular shape
5. Blocks very large, as big as houses

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Mafic Lava

• Dark colored (when hardened)
• Rich in Mg (magnesium) and Fe (iron)
• Forms oceanic crust.
• Mafic lava has a low viscosity and flows easily.
• Seen in slow erupting Shield Volcanoes and
  hardening into Basalt (extrusive) or Gabbro
  (instrusive)
•                
• Dominant at Mid-Ocean ridges, Oceanic Hot Spots
  (Shield Volcanoes of Hawaii), Island Arcs and can
  be found at Rift Valleys, Continental Hot Spots
  (Yellowstone). 

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Shield volcanoes

• gentle-sloping
• basaltic lava flows

At hot spots
-Compressive forces -Mafic lava
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Mauna Loa in Background Kilaeua is Behind
Mauna Loa
Mauna Kea Shield volcano Hot Spot Basalt
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Felsic Lava

• lighter colored (when hardened), rich in Si
  (silica). Forms continental crust.
• Felsic lava has a high viscosity and DOES NOT
  FLOW EASILY.
• Seen in continental Composite or Stratovolcanoes
  and result in EXPLOSIVE eruptions.  Ex. Cascade
  Mts. and Mt. St. Helens.  Can harden into granite
  (intrustive) and less likely rhyolite
  (extrusive).
• Dominant at Oceanic Continental Convergent plate
  boundaries/subduction zones and can be found at
  Continental Hot Spots (Yellowstone). 

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Composite (Strato-) volcanoes
Encountered at subduction zones
-andesitic composition -felsic lava -steep cones,
explosive
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Mt Rainier example of composite volcano
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Guagua Pichincha, Ecuador Quito in
foreground Composite volcanoes explosive
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Why do shield and composite volcanoes differ in
composition?
Mafic magmas rise along fractures through the
basaltic layer. Due to the absence of granitic
crustal layer, magmas are not changed in
composition and they form basaltic volcanoes.
Mountainous belts have thick roots of Felsic rise
slowly or intermittently along fractures in the
crust during passage through the granite layer,
magmas are commonly modified or changed in
composition and erupt on the surface to form
volcanoes constructed of granitic rocks.
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Cinder Cones

• Made of only pyroclastic rocks
• Build cone-shaped hill
• Most erupt only once
• Low level eruptions
• Paricutin, Mexico

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Volcanism at Mid-Ocean Ridges

• Majority of Earths volcanism
• Hydrothermal vents
• Chimney-like structures Black Smokers
• Sulfur-bearing minerals or Sulfides
• Incredibly diverse ecosystems, chemosynthesis

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Importance of Volcanism

• Eruptions can affect climate
• ex. Mt. Tambora eruption 1816 ? The Year Without
  Summer
• Origin of life on earth
• Some theories suggest life began at mid-ocean
  ridges in chemosynthetic environments

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Complex Mountains

• continental-continental collision
• tend to have a little of everything
  volcanoes,folds, thrust faults, normal
• faults

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ALPS
HIMALAYAS
View of Everest and Khumbu ice fall from Kala
Patar, Nepal Himalayas
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Mountain orogeny summary

• Orogeny mountain building event
• Plate tectonics used to explain mountain
  building
• Plate collisions- 3 types
• Forces tension, compression, shear
• Mountain types faulted, folded, volcanic,
  complex
• Examples of each type
• Types of volcanoes
• Types of Lava
• Importance of volcanism