Formation of the Appalachians

Appalachian Mountain Building

Nov 17, 2009 Alexandra Matiella Novak

Some rocks in the core of the Appalachian Mountains are more than 1 billion years old and construction of the mountains relates to the Supercontinent Pangea.

The oldest rocks within the core of the Appalachian Mountains are more than one billion years old and formed during a time when there was one supercontinent surrounded by one massive ocean. The break-up of this continent, the rising of sea-levels, volcanic activity and structural deformation of crust over millions of years, all played a role in creating the Appalachian Mountains.

North America and the Supercontinent Pangea

Over a billion years ago, all of today's present continents were joined together to form one massive piece of super continental crust surrounded by one massive ocean. This continent is referred to as Pangea and evidence of its existence is still present today. Then, about 750 million years ago, convection of the underlying mantle cause the crust to stretch and pull apart so that a huge basin formed. This basin is called the Ocoee basin and it formed in the areas that are now the western Carolinas, eastern Tennessee and northern Georgia. As the crust continued to stretch and the basin got deeper, sediment from the surrounding hills was transported to the basin by inland sea flooding. This thick sedimentary layer is what makes up the bedrock of the Great Smoky Mountains.

The breaking apart of Pangea also caused crust to thin so that magma was able to break through the surface. Volcanic activity occurred in the region at the same time as the sediments were being transported to the Ocoee basin. This volcanic activity ranged from gently erupting basaltic lava flows to more violent eruptions like that of Mt. St. Helens. This volcanic activity occurred in areas that are now Virginia, the Carolinas and Georgia and volcanic rocks are still present in these areas today.

Mountain Building from Continental Collision

About 540 million years ago, Pangea was stretched so thin that it split into many smaller continents that then drifted apart from each other. Seawater flooded lower areas of crust such as most of the North American continent, including the entire portion of the continent that is today the United States. These early continents continued to diverge until about 470 million years ago when the direction of plate movement reversed direction. The continental crust that today makes up the United States and Africa crashed into each other about 270 million years ago resulting in sever deformation of crust along the eastern margin of the ancestral North American continent and western margin of the ancestral African continent.

During collision, portions of crust were buried and melted to form plutons. Other portions of crust were crushed together causing immense heat and pressure so that the crust re-crystallized. From this tectonic activity, granite formations and metamorphic rock formations were created. Further collision caused these rock formations to fold and bend upwards to form what is today the Appalachian Mountains.

Then about 240 million years ago and after the formation of the Appalachians ceased, plate tectonics once again reversed direction so that the ancestral African continent and the ancestral North American continent were pulled apart. This direction of plate tectonics is still present today as the Atlantic Ocean continues to widen through the divergent activity of the mid-Atlantic Rift system.

Mountain Building

Rock Slide Caught on Tape

Source:

US Geological Survey: America's Volcanic Past and the Appalachian Mountains

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The Appalachian Mountains