Dedham Granite

[1] The Dedham granite was formed during the Ediacaran Period of the Precambrian era about 610 million years ago and is one of the oldest rocks in the Boston basin.

[2] The Dedham granite formed due to the interactions of two land structures - the Avalon microcontinent and the Gondwana supercontinent.

During the collision large amounts of magma came from the Avalon volcanic chain and swallowed the edge of the continental shelf which created deposits of Dedham granite throughout Massachusetts.

This is why there are also deposits of Dedham granite found in Africa since the formation of the rock occurred before the major continental movement.

Dedham Granite includes dioritic rock near Scituate and Cohasset and Barefoot Hills Quartz Monzonite.

[1] Dates on two samples from Sheffield Heights indicate that the diorite and granite are part of the Dedham North suite.

Dedham North Granite has a compositionally highly variable suite ranging from leucogranites to granodiorites, tonalites, and quartz diorite.