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-faulting2) Volcanic Activity
Other processes: Metamorphism, intrusions: batholiths, etc.
TYPES OF MOUNTAINS(according to their origin)
• Fault-block: tension, normal faultingex. Sierra Nevada, Wasatch, Grant Tetons
• Folded: compression, reverse faultingex. Appalachians, Alps, Himalayas, Urals, Atlas, Andes
• Volcanic: Shield and compositeex. Cascades, Mid-Ocean Ridges, Oceanic Hot Spots* Dome Mts: similar to volcanic, Adirondacks, Black Hills
• Complex: mixture of most of the aboveex. 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)
HANGING WALL
1. Fault-block mountainslarge areas widely broken up by faults
•Force: TENSION•Footwall moves up relative to hanging wall
Normal fault
Tilted fault-block range: Sierra Nevada from east,Steep side of block fault; Ansel Adams photo
Tilted Fault-blockSierra Nevada from westSide, low angle
Yosemite valley the result Of glaciation on low-anglerelief
Central cores consists of
intrusive igneous rocks
(granite).
Half Dome is a core (batholith)
that was exposed by erosion,
Batholith
Wasatch RangeFrom Salt Lake City
Typically fault-Block system
Grand Tetons: another fault-block system
Alternating normal faults lead to a characteristic pattern called a“horst and graben” system. An area under tension will often havemultiple mountain ranges as a result.
Horst and graben
Horst and Graben Landscapes
Figure 12.14
•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 fromBaja California
Sierra Nevada and Wasatch Ranges part of this system
Basin and Range province:
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 kilometersAlps are a great example
Flatirons(Boulder, CO)Classic example of high-angle reverse faults-> Form “Sawtooth Mtns”due to differential erosion
Seal rock
White Cloud peak
SAWTOOTH RANGE,IDAHO
Alice Lake
•Thrust (reverse) faults main cause of folded mountains
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)
AlternatingAnticlines andSynclines
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,
Types of Volcanic Material
1. Pyroclastic material: rock fragments ejected from volcano
2. Ash: less than 2 mm in diameter3. Dust: less than .25 mm diameter4. Bombs: spinning cooling large blocks of
material, cool to circular shape5. Blocks: very large, as big as houses
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).
Shield volcanoes
-Compressive forces-Mafic lava
At hot spots•gentle-sloping•basaltic lava flows
Mauna Kea
Shield volcanoHot SpotBasalt
Mauna Loa inBackground
Kilaeua is Behind MaunaLoa
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
-andesitic composition-felsic lava-steep cones, explosive
Encountered at subduction zones
Mt Rainier:
example of composite volcano
Guagua Pichincha, EcuadorQuito in foregroundComposite 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• 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 climateex. 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
•continental-continental collision•tend to have a little of everything: volcanoes,folds, thrust faults, normalfaults
Complex Mountains
ALPS
HIMALAYAS
View of Everest andKhumbu 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