New England is a region in the North Eastern United States consisting of the states Rhode Island, Connecticut, Massachusetts, New Hampshire, Vermont, and Maine. Most of New England consists geologically of volcanic island arcs that accreted onto the eastern edge of the Laurentian Craton in prehistoric times. Much of the bedrock found in New England is heavily metamorphosed due to the numerous mountain building events that occurred in the region. The most recent rock layers are glacial conglomerates.
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Cratonic New England
In the Archean Eon Western Massachusetts and Vermont were the eastern edge of Laurentia (now the Canadian Shield). Laurentia is believed to have originated at the end of the Hadean, making it one of the oldest regions with continental crust, as evidenced by the discovery of Acasta Gneiss in Canada. At the end of the Hadean massive eruptions of felsic lava became cool enough to form permanent crust. The felsic nature of Laurentia allowed it to float over the denser ocean basins that surrounded it, so it was not submerged under the then-forming oceans. During the Archean Eon the surface of New England was a coastal desert covered by silica-rich sediments with outcroppings of granite bedrock.
Orogenic Periods
Starting in the Paleozoic Era the supercontinent Pannotia began to break up, forming smaller continents including Laurentia (North America and Greenland), Gondwana, Baltica, and Siberia. At the same time sea levels were rising, which resulted in the flooding of most of the continents with shallow epicontinental seas. This was followed by three periods of extensive orogeny.
Taconic
During the Middle Ordovician volcanic island arcs collided with the east coast of North America causing extensive metamorphism, faulting, and uplift, the result of which was the Taconic Mountains on the border of New York and New England.
Acadian
The Acadian orogeny took place during the middle to late Devonian. Following the subduction of the Iapetus Ocean floor, the microcontinent Avalonia slammed into eastern North America, which caused another period of metamorphism, faulting, and mountain building.
Alleghenian
The Alleghenian Orogeny occurred during the late Paleozoic and was the result of the collision of Africa with North America during the formation of Pangea. The collision events produced tremendous occurrences of thrust faults, folding, and metamophism. As a result of this collision event a huge mountain belt formed that ran up the east coast of North America into Canada and Baltica, which had collided with Greenland and northern North America. Although the modern-day Appalachian Mountains have been heavily weathered over time, they were thought to once rival the Himalayas in size.