When discussing the plate tectonics of Connecticut, it is vital for students to have a bedrock map of Connecticut. This can be obtained from the Department of Environmental’s publication and map division. This map comes in a variety of sizes (postcard size on up). It shows the different terranes, bedrocks and faults. It is color coded for easier interpretation.
Our history can be summed up in two words—”crunch and crack.” At one time, Connecticut was somewhere between 500 -3000 miles across, but today Connecticut is only about 100 miles across. This is due to the formation of the giant supercontinent called Pangaea. (Bell, 1985)
Prior to the formation of Pangaea, the Atlantic Ocean did not exist. Instead, another water body called the Iapetos Ocean existed between the land masses of Proto—North America and Avalonia. (DEP,1990)
From 450 to 250 million years ago, during the Paleozoic Era, several plates collided (crunch) to form the giant supercontinent called Pangaea. Connecticut was located in the middle of this and was vastly changed. Aside from the previously mentioned reduction in size, the Appalachian Mountains formed. At one time they were the world’s largest. It is estimated that they were between 20,000 to 30,000 feet high.(Bell, 1985)
During this episode of plate collision, Avalonia, a continent believed to be part of the African plate collided with the continent of Proto-North America. This action closed up the Iapetos Ocean and its subduction zone. This big “crunch” initiated processes of deformation and metamorphism, thus creating schists, gneisses and granites which are exposed today in our state. (DEP, 1990)
Further evidence for this continental collision comes from the analysis of the terranes that make up Connecticut.Also, the rocks within these terranes provide even more conclusions. The marble found in the “marble valley’of connecticut (an area in the north-western part) is evidence of the former Iapetos Ocean. Marble forms from the metamorphism of limestone and limestone forms when beds of shells, corals and lime-rich muds become cemented together. A large shelf called a carbonate bank forms from this in tropical ocean waters. Due to this marble it is thought that the carbonate bank found along the eastern edge of the Proto—North America terrane formed in this manner. (Bell, 1985)
Along with this is the fact that Pangaea and thus Connecticut was located far south from its current condition. Located closer to the equator with a climate similar to Central America. This created a tropical paradise in Connecticut. (Bell, 1985) At the time that Pangaea formed, the oceans supported most of the plants and animals. Our crust is forever shifting and even though plates may move on the average only one inch per year, this is a constant process. About 200 million years after Pangaea formed, the tectonic processes reversed and Pangaea began splitting apart (Connecticut geologists refer to this as the “Great Crack”). This occurred during the Mesozoic Era. This breakup divided the Appalachians into a series of flat-bottomed rift valleys and high mountain ranges. (Bell, 1985)
At the time of the breakup of Pangaea, Connecticut had forests, dinosaurs and mammals. Fossil life will be discussed more in detail later on. Also, the Atlantic Ocean formed and is still growing today.(Little, 1986)