Transcript WHAT IS OROGENY? Processes of mtn building

Mountain Orogeny
Three types of plate boundary
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.
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
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)
1. Fault-block mountains
large areas widely broken up by faults
Normal fault
HANGING WALL
•Force: TENSION
•Footwall moves up
relative to hanging
wall
Tilted fault-block range: Sierra Nevada from east,
Steep side of block fault; Ansel Adams photo
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
Wasatch Range
From Salt Lake City
Typically faultBlock system
Grand Tetons: another fault-block system
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.
Horst and Graben Landscapes
Figure 12.14
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
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 100’s of kilometers
Alps are a great example
Flatirons
(Boulder, CO)
Classic example of
high-angle reverse faults
-> Form “Sawtooth Mtns”
due to differential erosion
Seal rock
SAWTOOTH RANGE,
IDAHO
Alice Lake
White Cloud peak
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
Classic folded terrain: well-developed anticline
Appalachian Mountains of the US
Atlas Mountains, Northern Africa
Zagros Crush Zone (Iran/Iraq)
Alternating
Anticlines and
Synclines
Volcanic mountains
• Shield
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Gradual slope, very tall to ocean floor, slow flowing eruptions,
composed of layers of lava
• Composite (Strato-)
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Explosive, made of pyroclastic material and lava. steep
• Cinder cone
• Very steep slopes, made of pyroclastic material,
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
Mafic Lava
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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).
Shield volcanoes
At hot spots
-Compressive forces
-Mafic lava
•gentle-sloping
•basaltic lava flows
Mauna Loa in
Background
Kilaeua is
Behind Mauna
Loa
Mauna Kea
Shield volcano
Hot Spot
Basalt
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).
Composite (Strato-) volcanoes
Encountered at subduction zones
-andesitic composition
-felsic lava
-steep cones, explosive
Mt Rainier:
example of composite volcano
Guagua Pichincha, Ecuador
Quito in foreground
Composite volcanoes explosive
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.
Cinder Cones
• Made of only
pyroclastic rocks
• Build cone-shaped hill
• Most erupt only once
• Low level eruptions
• Paricutin, Mexico
Volcanism at Mid-Ocean Ridges
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Majority of Earth’s volcanism
Hydrothermal vents
Chimney-like structures “Black Smokers”
Sulfur-bearing minerals or Sulfides
Incredibly diverse ecosystems, chemosynthesis
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 midocean ridges in chemosynthetic
environments
Complex Mountains
•continental-continental collision
•tend to have a little of everything:
volcanoes,folds, thrust faults, normal
faults
ALPS
HIMALAYAS
View of Everest and
Khumbu ice fall from
Kala Patar, Nepal
Himalayas
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