Appalachian Mountain Building

1
Appalachian Mountain Building

• Chapter 20 Section 2
• Lauren Bauschard
• Jamie Reed

2
Orogeny

• Orogeny is the process that for all mountain
  ranges.
• Orogeny results in broad, linear regions of
  deformation known as orogenic belts.
• Most orogenic belts are associated with plate
  boundaries.
• The greatest variety and
• the tallest of these belts
• Are found at convergent
• Boundaries.

3
Oceanic-Oceanic Convergence

• When an oceanic plate converges with another
  oceanic plate, one plate descends into the mantle
  to create a subduction zone.
• As parts of the subducted plate melt, magma is
  forced upward to form a series of volcanic peaks
  called an island arc complex.

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Oceanic- Continental Convergence

• Same as O-O boundaries in that convergence along
  both creates subduction zones and trenches.
• Convergence between O-C plates can produce major
  mountain belts
• The descending oceanic plate forces the edge of
  the continental plate upwards. This uplift marks
  the beginning of orogeny.
• In addition to uplift, compressive forces may
  cause the continental crust to fold and thicken.
  

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Oceanic-Continental Convergence
6
Continental-Continental Convergence

• Continental crust cannot be subducted into the
  mantle when two plates converge because of its
  relatively low density.
• Instead, the energy associated with the collision
  is transferred to the crust involved, which
  becomes highly folded and faulted.

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Continental-Continental
8
The Early Appalachians

• Tectonic history of the Appalachian Mountains
  started about 700 to 800 years ago.
• Ancestral North America separated from ancestral
  Africa along two divergent boundaries to form two
  oceans
• A continental fragment was located between the
  two divergent boundaries.

9
700-600 M.Y.B.P

• During this time the directions of plate motions
  reversed.
• The ancestral Atlantic Ocean began to close as
  the plates converged.
• This convergence resulted in the formation of a
  subduction zone and a volcanic island arc east of
  ancestral North America.

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700-600 M.Y.B.P
11
500-400 M.Y.P.B.

• At this time the continental fragment became
  attached to ancestral North America.
• The highlt metamorphosed rocks, were thrust over
  younger rocks to become the Blue Ridge Province.

12
500-400 M.Y.B.P.
13
400-300 M.Y.B.P.

• At this time the island arc became attached to
  North America.
• This is proved in the Piedmont Province.
• These rocks were also faulted over the continent
  pushing the Blue Ridge rocks farther west.

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400-300 M.Y.B.P.
15
300-260 M.Y.B.P.

• During this time the ancestral Atlantic Ocean
  closed as ancestral Africa, Europe, and South
  America collided with ancestral North America to
  form Pangaea.
• This is when the modern Atlantic Ocean formed.

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300-260 M.Y.B.P.