If erosion stripped off the top of a dome, what would be found?

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• If erosion stripped off the top of a dome, what
  would be found?
• a. The oldest rocks are exposed in the center.
• b. The oldest rocks are exposed along the edges
  of the dome.
• c. The youngest rocks are exposed in the
  center.
• d. The rocks in the center are the same age as
  those along the edges.
• The convergence of two continental plates would
  produce
• a. trenches. c. folded mountains.
• b. rift valleys. d. island arcs.
• What type of mountains are produced by
  ocean-ocean convergence?
• a. a continental volcanic arc
• b. mainly volcanic mountains
• c. parallel belts of uplifted mountains and
  volcanic mountains
• d. parallel belts of folded mountains and
  volcanic mountains

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Mountain Formation

• Chapter 11, Section 3

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Mountain Building at Convergent Boundaries

• With the original development of the theory of
  plate tectonics, an accepted model for orogenesis
  emerged
• Most mountain building occurs at convergent plate
  boundaries
• Colliding plates provide the compressional forces
  that fold, fault, and metamorphose the thick
  layers of sediments deposited at the edges of
  landmasses

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Ocean-Ocean Convergence

• Ocean-ocean convergence mainly produces volcanic
  mountains
• These features tend to be long-lived
• The accumulation of sediment scraped off of the
  subducting plate increases the volume of the
  crust
• Examples Aleutian Islands (Alaska) and Japan

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Development of Mature Island Arc
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The Japanese Islands
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Ocean-Continental Convergence

• The convergence of the continental block and the
  subduction of the oceanic plate leads to
  deformation and metamorphism of the continental
  margin
• Partial melting of mantle rock above the
  subducting plate generates magma that migrates
  upward
• Accretionary wedge - the accumulation of
  different sedimentary and metamorphic rocks with
  some scraps of ocean crust that gathers on the
  landward side of a trench
• The types of mountains formed by
  ocean-continental convergence are volcanic
  mountains and folded mountains
• Examples Andes (South America) and Cascades

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Ocean-Continental Convergence 1
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Ocean-Continental Convergence 2
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Ocean-Continental Convergence 3
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Andes Mountains
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Continent-Continent Convergence

• Continental crust floats too much to be subducted
• At a convergent boundary between two plates
  carrying continental crust, a collision between
  the continental fragments will result and form
  folded mountains
• Most of the oceanic crust that separated
  landmasses, before a collision, is subducted, but
  some gets caught up in a collision zone and
  raised above sea level
• Examples Himalayas (Asia), Urals (Russia), and
  Appalachians

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Continent-Continent Convergence
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Concept Check

• Why cant continental crust be subducted?

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Mountain Building at Divergent Boundaries

• Most mountains are formed at convergent
  boundaries, but some are formed at divergent
  boundaries
• The mountains that form along ocean ridges at
  divergent plate boundaries are fault-block type
  mountains
• Example the 65,000 kilometer long mid-ocean
  ridge system

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Mid-Atlantic Ridge
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Concept Check

• Where is the longest mountain range?

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Major Mountainous Landforms of the Western U.S.
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Continental Accretion

• Accretion the process by which fragments
  collide with a continental plate and become stuck
  or embedded into the continent
• Terrane any crustal fragment that has a
  geologic history distinct from the adjoining
  terranes
• Terranes can contain anything from sediment off
  the ocean floor to volcanic island arcs
• The newly added material increases the width and
  thickness of the continental crust
• The accretion of larger crustal fragments, such
  as a mature island arc (Hawaii), may result in a
  mountain range
• Because of its buoyancy, an island arc will not
  subduct beneath the continental plate

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Submerged Crustal Fragments and Oceanic Plateaus
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Collision of Volcanic Island Arc with a Continent
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Accreted Terranes
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Concept Check

• What is a terrane?

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Isostasy

• Isostasy concept of a floating crust in
  gravitational balance
• Many mountain belts stand high above the surface
  because they have buoyant (less dense) crustal
  roots that extend deep into the mantle
• Isostatic adjustment the processes of
  establishing a new level of gravitational
  equilibrium
• As weight is added to the top of a mountain, the
  crust subsides, and as weight is lifted, the
  crust will rebound
• Because of isostasy, deformed and thickened crust
  will undergo regional uplift both during mountain
  building and for a long period afterward

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Isostasy
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Erosion and Isostatic Adjustment
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Isostasy in Action Iceberg
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Assignment

• Read Chapter 11, Section 3 (pg. 317-324)
• Do Section 11.3 Assessment 1-7 (pg. 324)
• Start Studying for the Unit 2 Test (Chapters 8-11)