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
Appalachian Mountain Expert
Earth Science Honors
Period 8
Dr. Houghton
13 May 2014
The Appalachian Mountains are one of the oldest mountain belts on the planet (1, Fig.
1). This mountain belt is present along the eastern portion of North America, from
Alabama, U.S to Newfoundland, Canada (1). The Appalachians are approximately
1,600 miles long and approximately 100 miles wide (1). They formed from a series of continental collisions that occurred over three mountain building events (orogenies), the
Taconic, Acadian, and Alleghanian Orogenies between 600 million years ago (mya) and
250 mya (1, 2).
More than one billion years ago, prior to the formation of the Appalachian mountains, the supercontinent Rodinia formed from the Grenville Orogenies (3). A component of this supercontinent, referred to as Laurentia or Proto-North America, formed the beginning of the present continent of North America (3, Fig. 2). Proto-North
America formed from collisions of smaller landmasses (3). These collisions manipulated the crust and led to the formation of mountains (3). Eventually, the supercontinent
Rodinia split and oceans emerged (3).

New England started to form between 465 mya to 400 mya (3). Two island arcs, the Taconic and Avalonian, drifted toward subduction zones (a zone of sinking crust along a plate boundary) off the coast of Proto-North America (3). The subduction zones probably formed as a result of the ancestral North Atlantic closing (2). The Taconic and
Avalonian island arcs formed near South America and Africa (3). Mountains formed from each island arc collision (3). The Taconic Orogeny occurred when the Taconic island arc collided with Proto-North America (3, Fig. 3). The Acadian Orogeny occurred when the Avalonian island arc collided with Proto-North America (3, Fig. 5). Mountains rose when the islands rode up over the Proto-North America landmass (3, Fig. 4, Fig.
6).
The final orogeny (the Alleghanian Orogeny) that led to the formation of the
Appalachian Mountains occurred about 425 mya (2, 3). Subduction zones developed around the Proto-North America continent and Gondwana continent (3). Gondwana was the continent that contained South America and Africa (3). Oceanic crust subducted drawing the landmasses closer to one another (3). Once the space between the continents was almost closed, the masses began to converge (3, Fig. 7). Gondwana rode up on top of Proto-North America and crushed and buried older mountains from the previous orogenies (3, Fig. 8). An extensive mountain belt formed at in the impact area of Gondwana and Proto-North America (3, Fig. 8).
Alfred Wegener proposed his radical hypothesis of Continental Drift (1). His hypothesis stated that the continents once formed one supercontinent; Pangaea then over time they divided into smaller separate continents and drifted to their current positions (1). Although Wegener had evidence to support his hypothesis, he could not

identify the mechanism responsible for this phenomenon (1). The lack of mechanism caused other scientists to reject his hypothesis (1). The orogenies of the Appalachian
Mountains were a significant part of the Pangaea (3, Fig. 9). When Proto-North America and Gondwana combined, sedimentary rocks, which formed at the bottom of the ocean, were forced to the surface becoming a part of the Appalachians (4). Compression of the sedimentary rocks produced heat and pressure that metamorphosed the sedimentary rock into metamorphic rock (4). Sedimentary rock is rock formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented (1). Metamorphic rock is rock formed by the alteration of preexisting rock inside of the Earth by heat and pressure (1). The Appalachians are mainly composed of metamorphic and igneous rocks, though sedimentary rocks are still present (4).
Throughout the formation of the Appalachian Mountains, the Earth’s surface and composition has undergone many changes (3). Energy from the continental collisions deformed and metamorphosed rocks (3). The energy affected material below the mountains of the first two orogenies (3). Folding and faulting (2), as well as erosion (3), manipulated the crust. The most recent changes in the Appalachian Mountains are a result of erosion and glaciation, not an orogeny (3). Ice sheets covered the geography of New England (3). As these ice sheets moved, they scoured rocks, uncovered previous geographic features and created new ones (3). The different environment forced organisms away and the glaciers left debris behind. These changes occurred only 55,000 and 18,000 years ago (3).

Works Cited
1. Tarbuck, Edward J., and Frederick K. Lutgens. Earth Science . Upper Saddle
River, NJ: Prentice Hall, 1997. Print.
2. Van Der Pluijm, Ben A., and Stephen Marshak. Earth Structure: An Introduction to Structural Geology and Tectonics . N.p.: WCB/ McGraw Hill, 1997. Print.
3. "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>.
4. "Rocks of the Appalachian/Piedmont." Rocks (n.d.): n. pag. The Paleontological
Research Institution. Web. 22 May 2014. <http://http://www.priweb.org/ed/
TFGuide/NE/rocks/rock_files2/rock_pdfs/ne_rocks2.pdf>.
5. "The Appalachians" 30 March 2008. HowStuffWorks.com.
<http://geography.howstuffworks.com/united-states/theappalachians.htm>
22 May 2014.
6. "Supercontinents - What You Don't Know." Bubblews . N.p., 10 June 2013. Web.
22 May 2014. <http://www.bubblews.com/news/640902-supercontinents
-what-you-don039t-know>.

Figure 1.
Appalachian Mountains range from Alabama to Newfoundland (5).

Figure 2.
Rodinia, at the center Proto-North America labeled as Laurentia (3).

Figure 3.
Taconic Orogeny (3.)

Figure 4.
Result of Taconic Orogeny (3).
Figure 5. Acadian Orogeny

Figure 6.
Result of Acadian Orogeny

Figure 7.
Alleghanian Orogeny (3).

Figure 8.
Result of Alleghanian Orogeny (3).

Figure 9.
Pangaea (6).