Additional Proterozoic crust was accreted 1,800—1,300 Mya, especially along the Laurentia—Greenland—Baltica margin. Laurentia and Baltica formed a coherent continental mass with southern Greenland and Labrador adjacent to the Arctic margin of Baltica. A magmatic arc extended from Laurentia through southern Greenland to northern Baltica. The breakup of Columbia began 1,600 Mya, including along the western margin of Laurentia and northern margin of Baltica (modern coordinates), and was completed c. 1,300—1,200 Mya, a period during which mafic dike swarms were emplaced, including MacKenzie and Sudbury in Laurentia.
Additional Proterozoic crust was accreted 1,800—1,300 Mya, especially along the Laurentia—Greenland—Baltica margin. Laurentia and Baltica formed a coherent continental mass with southern Greenland and Labrador adjacent to the Arctic margin of Baltica. A magmatic arc extended from Laurentia through southern Greenland to northern Baltica. The breakup of Columbia began 1,600 Mya, including along the western margin of Laurentia and northern margin of Baltica (modern coordinates), and was completed c. 1300—1,200 Mya, a period during which mafic dike swarms were emplaced, including MacKenzie and Sudbury in Laurentia.