A Summary Of Appalachian Mountain Building Events, The Taconic, Acadian
And Alleghanian Orogenies, The Effects Of The Laurentide Ice Sheet On The
New England Landscape, And An Overview Of The Rock Cycle And Its Relation
To The Types Of Rocks Located In The Appalachian Mountains, Particularly In
New Hampshire
Appalachia Expert
Earth Science Honors
Period 4
Dr. Houghton
5/6/2014
The Appalachian Mountain Range is a long string of mountains that run from
Newfoundland to Alabama (Fig. 1). The range is about 1,600 miles long and
about 100 miles wide (1). Their formation started about 600 million years ago
(mya). The process of their formation is broken up into three different mountain
building events (orogenies, 1).
The formation of the Appalachian Mountains began around 600 mya when
the ancestral North Atlantic Ocean began to close. As the ocean began to close,
two-subduction zones also likely formed: one off the coast of Africa and the other
off the coast of the proto-North American (Laurasia, 1, Fig. 2). This led to the
formation of the Taconic Island Arc and the Avalonian island arc (1, Fig. 2).
The mountain building began approximately 450-500 mya. At this time, the
small the Taconic Island Arc and the North American continent collided (Fig. 2).
Through this process, the crust of North America deformed and crystalline rock
began to form from the remnants of the collision. This formed the first of the
mountains added to the Appalachian mountain chain, the Western Piedmont
region and Blue Ridge Mountains (1). This was known as the Taconic Orogeny
(2, Fig. 2).
The second part of the mountain building process happened 400 mya.
During this process the Ancestral North Atlantic continued to close and the
Avalonian arc collided with the Proto-North American continent. The islands were
added to the existing start of mountains, and caused them to grow larger. The
subduction zone that was present near the Avalonian Island Arc was now located
off coast of North America (1). This process is known as the Arcadian Orogeny
(2, Fig. 2).
The third and final Orogeny occurred 250-300 million years ago. This final
step resulted in the collision of the Proto-North American Continent with the
Proto-African and European Continents. The African Plate and North American
Plate formed a convergent boundary, where the African Plate slid underneath the
North American Plate. The convergent boundary then connected the North
American Continent with the African continent. The force of one plate sliding
under the other resulted in the upward force of the North American Boundary that
in turn formed the remainder of the Appalachian Mountains (1). This final
Orogeny is known as the Allegheny Orogeny (2, Fig. 2).
During the formation of the Appalachian Mountains, the rocks that make
up the mountains went through many changes (Fig. 3). There are three types of
rocks: igneous, metamorphic and sedimentary (1, Fig. 3). Igneous rocks are
formed when hot magma cools and crystallizes. There are two types of igneous
rocks, intrusive and extrusive igneous rocks. Intrusive cool very slowly and
usually contain a large amount of crystal while extrusive cool almost immediately
and contain little to no crystals (1, Fig. 3). Metamorphic rocks are made from
preexisting rocks that are usually changing from one rock type to another (1, Fig.
3). Sedimentary rocks form when sediments are compacted and cemented.
Weathering and erosion over time helps these rocks settle and form into the
sedimentary rocks (1, Fig. 3). All three rocks can go through a series of changes,
in what is known as the rock cycle. During the cycle many factors, such as
weathering, erosion, melting and crystallization affect and change rocks from one
form to another (1, Fig. 3).
Before the continents moved to their current position, all the continents
likely were connected in one supercontinent known as Pangaea (3, Fig. 4). Each
continent was located on a floating piece of land known as a plate. The plates,
which are located in the lithosphere, are constantly in motion. The continents on
each plate have drifted apart over the past 300 millions years (3). The three
mountain building events (Orogenies) led to the landmasses of North America
and Africa combining to form Pangaea. There were many sedimentary rocks that
formed on the bottom of the ocean that were forced up to form part of the
Appalachian Mountains. As the plates collided, the African Plate gave way and
slid under the North American Plate. The sedimentary rocks built up over time
and formed the huge mountains. But because of all the squeezing and
compressing of the rocks, heat was generated and eventually much of the
sedimentary rock underwent metamorphosis and turned into metamorphic rock
(Fig. 3). This is the reason that New Hampshire rocks are metamorphic and not
sedimentary (3). Though, many sedimentary rocks remain throughout the
Appalachian Mountains.
The Appalachian Mountains have undergone drastic changes since their
formation mya. The most recent changes include glaciation, and weathering and
erosion. About 55,000 and 18,000 years ago, the Laurentide Ice Sheet covered
Canada and all of New England in ice (Fig. 5). When glaciers move they carry
loose rocks and sediments with them and can transport them great distances.
The Laurentide ice sheet was the main cause of many large rock deposits
located around New England (4).
Work Cited:
1) Tarbuck, Edward J., and Frederick K. Lutgens. Earth Science. Upper Saddle River,
NJ:
Prentice Hall, 1997. Print.
2) "Building the Northern Appalachian Mountains and New England - Jamestown RI
Visitor Information." Jamestown RI. Web. 08 Apr. 2012.
<http://www.jamestown-ri.info/northern_appalachians.htm>.
3) Hoffman, Doug L. "The Resilient Earth." Appalachian Mountains Rock Ice Age. 12
Nov.
2009. Web. 08 Apr. 2012.
<http://www.theresilientearth.com/?q=content/appalachian-mountains-rock-iceage>.
4) Rittenour, Tammy M. "ICE AGES IN NEW ENGLAND." Ice Ages in New England.
Web. 10 Apr. 2012. <http://www.bio.umass.edu/biology/conn.river/iceages.html>.
5) "Landforms of North America, Mountain Ranges of North America, United
States Landforms, Map of the Rocky Mountains - Worldatlas.com."
Landforms of North America, Mountain Ranges of North America, United
States Landforms, Map of the Rocky Mountains - Worldatlas.com. N.p.,
n.d. Web. 08 May 2014.
6) "Alleghanian Orogeny." Wikipedia. Wikimedia Foundation, 04 Aug. 2014. Web.
08 May 2014.
7) "The Rock Cycle." The Rock Cycle. N.p., n.d. Web. 08 May 2014.
8) "Plate Tectonics." Plate Tectonics. N.p., n.d. Web. 08 May 2014.
9) "Glaciers; Where It All Began - Acadia National Park." Glaciers; Where It All
Began - Acadia National Park. N.p., n.d. Web. 08 May 2014.
Figure 1. Major Mountain Ranges of the North American Landscape (5).
Figure 2. How the Appalachian Mountains formed through the three Mountain
building events (6).
Figure 3. How rocks change from one form to another during the rock cycle (7).
Figure 4. Pangaea and the associated oceans, seas and Proto-continents (8).
Figure 5. The formation, advance and retreat of the Laurentide Ice Sheet (9).