Tectonic History of the Boston Basin
The geological history of Boston starts with the Grenville Mountains. These mountains were formed when early North America collided with another continent, Baltica. The mountains stretched from Canada to Mexico, cutting across present day western Massachusetts. When the mountains weathered and eroded they formed the wide flat coastline of New England.
The next step in Boston’s history is with another mountain chain, the Avalon Mountains. 570 million years ago North America, which was near the Equator, collided with the ancient continent Gondwana, creating a subduction zone. This subduction zone's volcanic activity led to the formation of the Avalon Terraine. The Boston Rift Basin was then formed due to the rifting along Gondwana and the mountains. Around 550 million years ago, Gondwana separated from the Avalon Terraine and began to move North-West. The Avalon Mountain chain became an island arc (Boston Geology).
During the same time, Boston’s most common bedrock types were formed. As the Avalon rifted apart, the rift became filled with sediments which later formed the Roxbury Conglomerate, Cambridge Argillite, and Cambridge Sandstone. These rocks are slightly metamorphosed, layered sedimentary rock (Geology of Boston).
The next step in Boston’s history is with another mountain chain, the Avalon Mountains. 570 million years ago North America, which was near the Equator, collided with the ancient continent Gondwana, creating a subduction zone. This subduction zone's volcanic activity led to the formation of the Avalon Terraine. The Boston Rift Basin was then formed due to the rifting along Gondwana and the mountains. Around 550 million years ago, Gondwana separated from the Avalon Terraine and began to move North-West. The Avalon Mountain chain became an island arc (Boston Geology).
During the same time, Boston’s most common bedrock types were formed. As the Avalon rifted apart, the rift became filled with sediments which later formed the Roxbury Conglomerate, Cambridge Argillite, and Cambridge Sandstone. These rocks are slightly metamorphosed, layered sedimentary rock (Geology of Boston).
About 380 millions years ago, Avalon collided with North America. This resulted in lots of metamorphic activity between the island arc and early North America.
Around 250 million years ago, the super continent, Pangaea, contained all the continents. Avalon was crushed in between Africa and Baltica, forming the Appalachian mountains. 200 million years ago, Pangaea rifted apart. The North American continent slowly moved to its present day location (Geology of Boston).
To continue to learn about Boston Basin's geological history, click below!